11/12/06 - To call the STEALTH Billet Upper receiver (LT-007) from LaRue Tactical a 'nice' piece of machine work would be an understatement. It's a beautiful piece of machine work. The STEALTH upper was designed to retain the overall 'look' of a standard receiver; and reveal its origin only upon close inspection to a trained eye. LaRue's intention was to produce a very high quality upper receiver for precision builds. That meant a 'square/true' receiver, with all critical datums and features/surfaces square to each other, with no misalignment of the bore. While it can be debated whether and how having a 'trued-up' receiver has a noticeable effect on accuracy, it sure is nice to know you're starting out with one. It definitely doesn't hurt. Reduced receiver flex is another step towards increased accuracy/consistancy under different shooting conditions and positions, and the STEALTH receiver has been beefed up and reinforced in those areas which LaRue feel are the important ones.

Every surface on the STEALTH is machined, and if you look closely, you can see the subtle evidence of the tool paths, which I think give the STEALTH a nice aesthetic, much like the machined receiver on the LMT MRP. The STEALTH is machined out of 7075 T6 and has a mil-spec type III hard anodized finish, which feels very slick over the machined surface. There are no sharp edges on this piece either. It's available from LaRue in A3 configuration, which means no M4 feed ramp cuts. The M4 feed ramp version is only available from LaRue dealers. The STEALTH weighs one ounce more than a standard M4 receiver, from the beefing up of critical areas. T-numbers are laser engraved on the top, along with the small STEALTH™ lettering in the last slot, usually covered by the BUIS. 'LARUE' is subtly machined into the right side of the receiver just in front of the charging handle.

I noticed these additional differences when comparing the STEALTH to a standard receiver:

• Geometry of the shell deflector - it's been beefed up and is slightly larger than the standard deflector. The transition from deflector to body is also smoothed out.
• Ejection port cover rod retention - beefed up a LOT and the c-clip retainer has been relocated to just in front of the cover, rather than in front of the lug. It has a cleaner overall look.
• Areas around ejection port and cam pin bump have been beefed up.
• A small scallop on the left side has been added to provide clearance for the bolt release catch which indicates that the wall thickness of the receiver has been increased in that area. Actually, I believe the wall thickness of the entire receiver 'tube' in which the bolt carrier rides has been increased, by comparing the diameter of the STEALTH to a standard.
• Transitions between surfaces more 'radiused' and smoothed out.

The LT-007

Port-side

Top

Bottom

Deflector close-up

Comparison to standard upper

I assembled the STEALTH with a White Oak Precision 20" stainless match barrel. I specified M4 feed ramp cuts on the barrel when I ordered it, but they were too shallow and overhung the cuts on the receiver so I had to deepen them. Not all barrel makers machine them to the same depth. Other than that, the barrel fit was perfect. The extension slid in with no noticeable play and was a tight fit the last .1" of travel before it seated snugly into the receiver. I picked a 20" barrel without flash hider as it's the same overall length as an 18" barrel with hider. The sucker is heavy, though.

Installing the LaRue 12.0 rail was a snap, as well. Seen below on this build is LaRue's steel low profile gas block LT-202. It's available in a number of different dimensions to fit different barrels. It's held in place by two set screws on the bottom. The gas block has an extended sleeve, so that when used with a barrel that has been drilled for taper pins, it covers up the unsightly holes for a clean look. The STEALTH is a good starting point for building a precision upper, when combined with a quality barrel. It's not limited to precision builds, and is just as suitable for shorter-barreled builds for those who just want higher quality, squared-up and better-than-standard (in my opinion) upper.

Low profile gas block

Installed on barrel

With 12.0 rail

Completed build

with TD bipod

with harris bipod

8/18/06 - When Vltor Weapons Systems debuted their VIS (Versatile Interface Structure) upper receiver/rail system at the 2006 SHOT Show, people also asked "since the VIS is made of a billet receiver joined with a rail, are you going to offer the new receiver by itself?". That made a lot of sense to Vltor to offer the receiver by itself, and here it is: the MUR (Modular Upper Receiver).
The MUR the receiver-only portion of the VIS. The only difference is in the material used. The MUR is machined from a billet of 7075-T6 aluminum whereas the VIS is 6013, as 7075 cannot be salt-brazed. It's hard coat anodized and dry film lubed on the inside. (note that all current MURs are now machined from forgings instead of billet).

The MUR is available in two versions - the 1A (bolt Assist model) and the 1S (Shell deflector model). A cutout in the right side of the receiver accepts either a shell deflector insert, or forward-assist/deflector insert, which give the MUR its 'Modular' name. However, the inserts are not meant to be switched out by the user, as improper assembly can cause damage to the receiver.
The 1A insert is a block of aluminum that houses the forward assist plunger and shell deflector. It's located further forward than the standard forward assist, which gets it out of the way of the receiver sling mount for lefties and a better location overall, in my opinion. It also provides more clearance for your finger when using an ambidextrous charging handle. The 1S insert is an aluminum shell deflector riveted to a stainless steel cover. The Vltor logo is laser engraved on both inserts.

Just for clarification, the MUR is not a tighter-spec receiver; it is built to true specs. It's not going to be a 'tighter fit' like an IPSC race gun might be with closer fitting parts, but it's going to have the proper dimensions as it's built to the exact tolerances (whereas some other receivers may not be). By having only two machine operations to machine a MUR, build up of manufacturing tolerances/references is reduced, ensuring that everything is square, like the bore to the top rail. When you use a MUR in an upper build, you can be assured that the barrel will be properly aligned and the rail/handguard will be square.

Vltor updated the look of the receiver by incorporating a more angular profile, reminiscent of the SR-25. I think it's aesthetically pleasing, and gives the rifle a slightly different look. The different cross section, and addition of material in key places makes the MUR stiffer than a standard upper receiver. It's been beefed up in areas that contribute to receiver flex which can cause misalignment of the barrel to the centerline of the receiver/bolt. The different profile at the front can affect installation of some rail systems that index the sides of the receiver to prevent rotation. The Troy Ind MRF-C I installed below is one of them, and I had to do a bit of filing on the barrel clamp 'ears' of the rail to make them fit the wider MUR. If your rail system doesn't index the sides of the receiver, no modification is necessary.
The MUR-1A model weighs 9.6 oz (slightly more than a standard receiver), and the MUR-1S weighs 8 oz (slightly less than a standard receiver).

MUR-1A and 1S

MUR-1A

MUR-1S

Left view

Top view

Bottom view

Besides the laser engraved markings on the left side of the receiver, there's a UID (Unique ID) code engraved on the top of the flattop, at the rear. It's a small square made up of a grid of tiny squares - some blank, some filled in. The DOD (Department Of Defense) requires DOD contracting companies to mark a UID on specified tangible assets for the purpose of tracking them through their useful life. More info here. It's sort of like a bar code and can hold 10,000 characters of information. The information in the UID on the MUR is the CAGE (Commercial and Government Entity) code for Abrams, manufacture date and serial number. Below the UID is the serial number and CAGE code printed out. Vltor's serial number is as follows: year/day/month (indicated by a letter - January = A and so on), and 4-digit serial number. The serial number of the 1S shown below is 610H0064, indicating that it was manufactured in 2006, on the 10th of August (H is the 8th letter), serial number 0064.
As of this writing, all MUR receivers come with M4 feed ramps only - I had to dremel M4 ramps in my standard barrel (shown below).

UID mark

M4 feed ramps

MUR-1A with Troy MRF-C

Ambi charging handle

So, why get a MUR? Most don't need to replace their standard receiver with a MUR. But some users will appreciate a stiffer, more rigid upper receiver that's correctly machined to spec, looks better (in my humble opinion) than the standard receiver, and the knowledge that it comes from Vltor, which I consider a leader in innovative and practical design in the firearms industry. Or sometimes it's just nice for us guys to have cool new toys.

Update 10/22/07 - One of the gripes that people have had is that the MUR was not compatible with the LaRue anti-rotation device, due to the MUR's non-standard outer profile at the front of the receiver. When I installed my LaRue handguard on a MUR, I had to cut off one side of the anti-rotation device. Many people modified their devices, or simply left them off altogether. Now, there's no need to do so. Vltor decided to change the contour slightly so that the MUR would be compatible with all handguards, including the LaRue anti-rotation device. All MURs shipping from Vltor now have this update, so if you plan on using a LaRue handguard, either order direct from Vltor or make sure you specify to your Vltor dealer that you want the LaRue-compatible one. The original MUR is the top one in the photos below, with my modified LaRue anti-rotation device installed, and the updated MUR is on the bottom with no handguard.

Changed areas (red arrows)

Updated MUR on the bottom

3/18/06 - PREVIEW - Vltor Weapons Systems debuted their VIS (Versatile Interface Structure) upper receiver/rail system at the 2006 SHOT Show. It's a one-piece upper receiver/rail system, initially manufactured in two separate pieces, then joined together by the salt dip brazing process. Because the term 'monolithic' refers to a homogeneous piece of material like the LMT MRP, I'll use the word 'Bi-lithic' to describe a permanantely-joined structure that forms a one-piece.
Brazing is the process of joining two pieces of metal with a solder or filler metal with a high melting point, just below the melting temperature of the base metal. Simplisticly, the salt dip process involves immersing the pre-heated pieces in a molten salt/brazing flux bath, which heats up the part quickly and uniformly. The melted filler metal flows between the joints through capillary action, and when removed and cooled, results in an extremely strong and high-quality joint. One of the advantages of salt-dip brazing is that it enables designs which might not be possible through a conventional machining process. It is this process that enables the VIS to have a outside-threaded receiver-barrel interface that will take a standard barrel. Don't let anyone tell you that Salt Dip Brazing is a weak process. Yes, the parent material loses the T6 hardness during the process, but can be re-hardened back to T6 in a furnace (which Vltor does in their facility).
Note that the following applies to the pre-production prototype pictured here - the production VIS will have minor changes, and I'll update this when it's available.
The VIS is designed as a Bi-lithic upper which takes any standard M4/AR-15 barrel. The only thing that needs to be changed is the barrel nut, which requires removal of the front sight base (a normally simple matter). The VIS comes with a proprietary barrel nut wrench. It's not meant to be a quick-change barrel system like the MRP, but it's possible to switch barrel assemblies relatively easily, if both have the barrel nuts already installed. No removal of the standard gas tube is needed.
The debate about receiver flex, monolithic/bi-lithic uppers vs. receiver/rail systems still goes on. I have no first hand experience in those matters so I'm not qualified to comment on it here, so the end user has to decide whether the added rigidity of a one-piece upper is needed. In my mind, less flex is good, whether or not I'll have a practical need for it. Having an uninterrupted top rail is also nice, as well as eliminating the possibility of a separate rail system loosening up and rotating.
The VIS will be offered in carbine (pictured here), mid-length, and rifle lengths. A low profile gas block will fit under the VIS so it's possible to have either a gas-block front sight, or a rail-mount front sight.
Receiver - The VIS receiver has a more angular cross section externally, reminiscent of the SR-25. It gives the AR a new look (more noticeable on the left side), and I find it quite appealing. The right side of the receiver has an interchangeable 'panel', just rear of the ejection port. The user has the choice of installing a shell deflector assembly with or without a forward assist.
Upper Handguard - The upper handguard consists of the top rail and two sides, all MIL-STD 1913 compliant. Max width is about 2.2". It's heavily ventilated. Pins in the forward and mid section hold the removable lower handguard in place.
Lower Handguard - The lower handguard is removable by flipping two levers, which disengage the mid pins in the upper handguard. The front of the lower handguard has cutouts which engage the front pins. Note that there will be changes to the lower handguard and added options in the production VIS.

Right views

Left view

Receiver left side closeup

Lower rail

Lower rail removed

Receiver right side

It will be unavoidable not to compare the VIS to the LMT MRP, so I snapped the comparison pic below. The MRP carbine upper is more of a mid-length and the mid-length VIS would probably be a better comparison. The VIS is slightly wider than the MRP - closer to a standard RIS or other rail systems out there. Beyond the different features listed above, there isn't much practical difference in functionality. The advantage that the VIS offers is a bi-lithic upper at a very reasonable price. When you look at the cost of a standard upper receiver and rail system, the VIS is extremely competitive, and I'm predicting will be a front runner on the list of people putting together new AR uppers.

MRP comparison

SOCOM flat earth furniture

Foliage green furniture

12/31/06 - Production version update - All three versions (carbine, midlength and rifle) of the VIS are now in production and available. Very little has been changed from the pre-production prototype shown above except that the material is now 6013 T6 instead of 6061 T6. There have been minor changes to the lower handguard and a re-designed latch. Instead of a small hole for bullet tip, the latch is now bent over to allow anything that will fit in there to be used to pry it up. It's tight, and designed that way, as the lower handguard isn't meant to be removed and replaced all the time. Provisions for mounting an M203 has also been added, and a rear mount is supplied with each kit. When I wrote the preview above, I wasn't able to disassemble the upper, so I've shown more photos of the un-barreled receiver below.

Midlength (top), carbine (below)

Top view

Mid

Mid bottom

New latch

Bottom rail removed

The VIS kits come with a proprietary barrel nut wrench, to torque the proprietary barrel nut. There's no indexing of the barrel nut needed, and proper torque can be achieved. The VIS barrel nut also allows the barrel to be installed with gas tube and block already in place. Besides salt dip brazing, Vltor is also experimenting with other methods of joining the receiver and handguard together to improve production flow, like simple heli-arch welding and a new process called friction stir welding. From their testing, they found that the weakest point is NOT the bonded area, but the material of the handguard and/or the upper receiver, which is strong enough to equal a standard forged upper.
As mentioned above, the VIS does not have a quick-change barrel, but it's definitely easier to change the barrel on a VIS than a standard upper, especially if you have a rail system installed. As long as the replacement barrel has been set up with a VIS barrel nut, the change should only take a few minutes. With the advantages of a monolithic upper, easier assembly than a standard receiver/handguard, and a price not far off from a quality receiver/handguard combo, the VIS looks like a very attractive option for new builds.

Barrel interface

Barrel nut

Barrel nut wrench

M203 bracket installed

Midlength kit

Rifle length kit

Midlength with M203

1/11/07 - Midlength VIS build - The reason I hadn't gotten a VIS when they came out was that I was waiting for Vltor's new gas block/flip up front sight assembly. My patience paid off, and Eric put this together for me. It's a Wilson 1/8 16" stainless barrel re-contoured with a continuous taper (to the gas block) per Eric's specs. Ops-Inc shoulder and mid-length gas system. Illustrated below with a couple of different optics; a Trijicon TA01NSN and a Nightforce 2.5-10 x 24 NXS scope. With the ACOG, it's setup up as a 'Recce' rifle.

Mid VIS

With NXS 2.5-10

'Recce' rifle

At the range

Here are more views of the Vltor front sight/gas block previewed in the M4K section below.

Folded

Flipped up

1/6/07 - PREVIEW - Vltor Weapons Systems debuted their new M4K upper at the 2007 SHOT show. It's built on a Vltor VIS-1, carbine length Bi-lithic upper receiver. The M4K enables an M203 to be mounted on a shorter barrel than an M4, resulting in a more compact package when maneuverability and compactness is a priority. It accomplishes that with a modified M4 barrel, and proprietary flash hider. Also shown is the new Vltor gas block with integral front sight. Photos were supplied by Vltor.

Receiver - VIS-1carbine length Bi-lithic upper receiver.
Barrel - The M4K barrel is a chrome-lined M4 barrel, shortened to approx 12.5". It uses a carbine-length gas system. The extra barrel length past the gas block adds reliability over a shorty of 10.3" or 11.5".
Vltor M4K Comp/Flash hider - The M4K flash hider incorporates the M203 barrel clamp/mount shoulder needed to attach the M203 to the weapon. Why not just cut the barrel forward of that shoulder? Vltor designed the M4K hider to be compatible with hider-mounted supressors like the HALO, which attach over the hider and tighten by butting up against the rear of the hider. If a crush washer is used, the supressor can be misaligned when tightened, as it doesn't have a nice shoulder to index against. By incorporating the M203 shoulder into the rear of the flash hider body, the crush washer/hider interface is eliminated, providing a good surface for supressor mounting. A blank-firing adapter groove is also included. The flash hider has five dual ports, and is non-indexing. Vltor will also offer a version without the M203 shoulder, as a direct replacement for the standard hider.

M4K left side

Right view

Vltor front sight/gas block

M4K hider Sight flipped up

Vltor Front Gas Block and Flip-Up front sight - The Vltor front gas block and flip-up front sight will look strangely familiar to some. Nope, it's not a copy of the KAC gas block with integral front sight. It's actually the other way around. Eric Kincel designed this gas block back in 1995 when he was with the now defunct Unitech - the gun division of knife makers Microtech. Unitech and KAC were embroiled in legal matters at that time, and eventually KAC acquired all the tooling to make the sight, and did, which evolved into the current KAC product. GG&G's flip up front gas block also owes its inspiration to the Unitech design. Eric has revived his Unitech design, and updated it for Vltor. It's an all-steel, flip-up design, with a spring loaded dual-plunger detent. There is no lock. If hit, the sight will fold down, rather than damage a locking mechanism. It incorporates a QD sling swivel cup mount, and uses an AK front sight post. The photo below shows the original Unitech front gas block that Eric designed a decade ago, and the new Vltor one. The gas block will be available in a both cross-bolt clamp and taper pinned versions.

Unitech (upper) and Vltor gas blocks

Vltor front sight/gas block

Sight flipped up

1/4/04 - The Lewis Machine & Tool (LMT) Monolithic Rail Platform (MRP) receiver differs from all previous ones for the AR15/M16 family in that it is monolithic - the rail platform and receiver are machine out of one piece of aluminum, instead of being separate (receiver and rail system). Why go this route? Some of the advantages to this system are that barrels can be switched in a minute with only a torx tip screwdriver/ratchet, the barrel is free floating, the top rail is continuous/uninterrupted, and the whole package can be made more compact. Back in January, Larry at Buffer Technologies kindly loaned me a carbine receiver with two barrels for T&E. A full-length/rifle upper is available and so are longer barrels. The first thing that hit me when I handled it was that it was more compact in person than in pictures. The workmanship and finish is just beautiful on this piece.
Receiver - The length of the receiver is about 16.25" long. Mil-std 1913 rails cover the entire length of the top of the receiver, sides and bottom of the rail portion, which is 2.0" wide without panels and 2.2" in height. This is the narrowest rail system I've measured. A KAC RAS is slightly less than 2.2" wide without panels and a slim line ARMS #50 is 3" wide (with side rails). The receiver without barrel is very light. I wish I had a scale, but I suspect the whole assembly is a bit lighter than a comparable conventional receiver/FF rail system/barrel assembly. The barrel is held into the receiver by two cross bolts, one of which engages a corresponding cutout in the bottom of the barrel/extension. The other tightens the receiver around the barrel extension - 'clamping it'. The bottom of the receiver under the barrel is slotted to allow the receiver to tighten around the barrel/extension when both bolts are torqued. Stainless steel threaded inserts on the other side of the receiver ensure durability of the threads. The barrels/receiver also come with M4 feed ramps.
Barrels - LMT currently offers chrome lined barrels in 10.5", 14.5" and 16" lengths (approx), and stainless steel barrels in 16" and 18" (approx). The chrome lined barrels are marked "5.56 NATO 1/7 CB". The gas tube is of standard diameter, but straight instead of kinked like the standard gas tube. A low profile gas block is protected by the handguard tube. The gas block is cross pinned to the barrel and the gas tube is held via a standard roll pin. The gas tube is supported at the receiver end by a bracket attached to the barrel.
Overall impressions - What more can I say - it's one of the coolest things for the M4 I've seen recently. It feels very lively - maybe because I'm used to all kinds of accessories hanging off my rail systems. Some may question the need for the interchangeable barrel system. Much of the comparisons have been based on cost (these are not cheap). You can buy two different length barreled uppers for the price of one MRP with two barrels. You can have dedicated optics on each of the two receivers whereas the MRP has to share optics. Repeatability and POI change concerns during barrel swaps have been voiced. I have not yet tested it myself but reliable sources have stated that repeatability in POI is good when a barrel is removed and replaced. Difference in bullet trajectory between 14.5 and 10.5 barrels are less of a concern (in my humble opinion). By definition, CQB distances will be short, and a tiny difference in trajectory over CQB distances will be unnoticeable. I'd sight in my optic with the long barrel, and leave it at that. Of course, I'd try to document the differences between POI between barrels if possible at known distances. The advantage I see to having this system instead of two separate upper is that a spare barrel is much lighter and compact to carry. If a soldier knows he is going to go door kicking, he can take that short CQB barrel out of his ruck/bag, and replace the longer barrel in a matter of minutes. There are advantages and disadvantages to every system, but I'll see you on the forums for that discussion :-) But keep an eye on LMT - I'm sure they've got more goodies up their sleeves.

MRP with 14.5" barrel installed, 10.5" on the side

Side view of the 2 cross bolts and barrel/gas tube

Bottom view of same. Note the slot in the bottom of the receiver

The cross bolts removed

Left side of the receiver showing SS threaded inserts

Views of low profile gas block

Inside of receiver showing M4 feed ramps

The business end

RAS, MRP and SIR slimline without rail panels

RAS, MRP and SIR slimline with rail panels

Now this one is set up with ARMS#40L rear BUIS and KAC front, Docter Optic, pre-production TD rail panels. The Docter sight is similar in idea to the Tasco Optima (now out of production). The Docter, however, is superior in almost every respect, being made out of stainless steel, brass and aluminum instead of plastic. The lens is made of two optical quality pieces of glass instead of plastic. There is no on-off switch; the sight turns on when exposed to light, and adjusts automatically for varying lighting conditions. This particular model has a 3.5 MOA dot. It's extremely light and small, and makes for a very streamlined setup. It's weather resistant, not waterproof, but a waterproof military model is available at twice the price. The top row of pics shows the Docter mounted on a GG&G mount, but I later changed this out to an ARMS #17DR throw lever mount (bottom row of pics). Also shown is the Yankee Hill offset mount, which makes a great light mount when combined with a 1" QD ring. It puts the light tailcap right under your thumb where it's activated easily.

Seen below is the M203 mounted on the top of an MRP. These pics were taken at the 2004 SHOT show by SULACO2.

MRP with '203 and Troy Ind. front sight

Top view of the M203 mount with SOPMOD stock and a block of aluminum that the MRP is machined out of

Closeup of the mount

Seen below is the rifle-length MRP with pre-production TD tan furniture and Vltor stock.

The 'beauty shot'

12/31/06 - This writeup has been a long time in coming, as the CASV-EL from Vltor Weapons Systems has been out a couple of years now. The original CASV was orignally offered by Abrams Airborne, and when Abrams acquired Vltor, Eric Kincel (general manager and head designer) re-designed the CASV specifically for the U.S. Navy, which allowed it to be installed at the user level without any modifications to the host weapon and also allow the attachment of the M203 grenade launcher. It was adopted by the U.S. Navy EOD (West Coast) in the tan version, and once that contract was fulfilled, Vltor offered it to the public in 3 colours - tan (ELT), black (EL) and OD green (ELG).

The CASV-EL is made entirely of aluminum, with the exception of the mounting hardware, which is stainless steel. It's basically designed for carbine-length gas systems like the M4 or M4 CQB 10.3" barreled upper, and attaches to the top of the flat top receiver without alteration to the host weapon or gunsmithing needed. The barrel remains free-floated; the handguard does not touch any part of the barrel except at the barrel nut. The 'EL' refers to ' extended length - the CASV 'extends' the available rail space past the front sight tower. The CASV-EL weighs less than 16 oz.

Parts - The CASV-EL doesn't have many separate components. There's the upper handguard assembly, which consists of the top rail and clamp, and the upper handguard. Then there's the lower handguard, plus the five bolt-on rail sections. The upper and lower handguard are bent aluminum sheet metal, formed into an octogonal cross-section. The lower handguard attaches and detaches by squeezing the two 'ears' at the front of the rail and pivoting it down. There are two 'hooks' at the rear of the lower handguard, which hook over pins in the upper handguard. To re-attach the lower handguard, it's hooked in the rear, then swung upward until the 'ears' snap into place in the upper handguard. Very quick, very simple. The lower handguard is removed when an M203 is a attached to the weapon.

Green CASV kit

Tan and black CASV's

Bottom

Lower handguard removed

Barrel nut interface

Installation - The way the CASV attaches is similar to the ARMS SIR, which has drawn comparisons between the two systems, as both clamp to the flattop of the receiver, and raise the top rail height. The CASV, however, is easier to install, and to remove and replace the lower handguard. To install the CASV, the plastic M4 handguards are removed, and the front sling swivel (if you're using the standard M4 sight tower). The top rail clamp is loosened, and the handguard assembly slipped onto the receiver, while pulling back on the delta ring. The inside of the handguard has a groove in which the top part of the barrel nut sits, so when that is engaged, the delta ring is allowed to spring forward and capture the rear of the handguard. The rail clamp is then tightened, and you're done.

The CASV-EL kit comes with four accessory rails (one 6", two 4" and two 2"). The top handguard has six inserts on each side for mounting the rails on the side. The bottom handguard has a row of inserts on the bottom at 6 o'clock, and also three inserts on each side at the 4:30 and 7:30 positions for mounting the rails at 45°.

Secured by delta ring

Top rail

Accessory rails installed

The main drawback to the CASV and any other top rail mounted system is that it raises the top rail. In the CASV's case, it raises it about .475". This limits the optics mounting options if you're trying to co-witness the irons to a dot sight. A low mount for an AImpoint is needed (like the LaRue RAS II mount). An EoTech (seen mounted above) will not co-witness; it's too high, and will need to be removed before the irons can be used. Although it's only about 2.05" wide (similar to other rail systems), that's without the side rails attached. Attaching the side rails for the mounting of accessories puts the accessories further out than on other rails systems (except the SIR). The CASV is meant to be used without rail covers, as the standoff distance between the barrel and the inside wall of the handguards is enough to keep them from getting too hot, so in that respect, it feels no wider than other rails. You only install the rails you need, and keep the rest off.

The advantages of the CASV over other rail systems is that it's probably the easiest free float rail to install. It's lightweight, rigid, and provides an uninterrupted top rail for mounting optics or aiming devices. The barrel is free floated so pressure on a vertical grip will not affect point of aim. The extended sides provide more real estate and options for mounting accessories, and also help protect the front sight base.

10/20/07 - The new CASV-M from Vltor Weapons Systems is the midlength version of the CASV-EL shown above. The CASV-M is designed to be used with a midlength gas system with any front sight/gas block, or with a carbine (or shorter) gas system with low profile gas block. Until now, midlength gas system users could use the CASV-EL, but the sight tower cutout would leave the midlength gas tube semi-exposed. The M covers the gas tube completely on a midlength system.

Differences between the EL and M - The CASV-M shares the same aluminum construction as the EL, and attachment/installation method. They share the same top rail and at first glance they look almost identical, but here are the main differences:

• The M is about .6" longer than the EL.
• There is no cutout at the front on the top for a carbine-length gas system front sight on the M. Instead of the cutout is a solid area forward of the top rail with two threaded inserts (more on this later).
• At the rear of the upper handguard assembly is a hole for a QD sling swivel. The swivel will not rotate all the way around.
• Three threaded inserts have been added at the rear of the upper 45° surfaces. If magnified optics are used, a mini-dot sight can be mounted there.

Tan CASV-M kit

Black, Green and Tan CASV-Ms

M (top), EL (bottom)

QD sling swivel hole

Top short rail and flip-up front sight - Forward of the top rail is that flat are with the two threaded inserts. A short length of rail, which is included in the kit can be installed to extend the top rail to the end of the upper handguard. A separately available flip-up front sight can also be installed. The sight uses a standard AR front sight post, and is spring detent loaded in the folded and deployed positions. It is compatible only with the CASV-M, and not any other rail system.

Top short rail

Top short rail installed

Flip up front sight

Installed, folded

Deployed

Illustrated below is the CASV-M installed on two Noveske uppers, both with low profile gas blocks installed underneath the handguards.

Low profile gas block inside

M on Noveske Diplomat barrel

M on carbine length gas system

12/24/08 - The new CASV-S from Vltor Weapons Systems is a bi-level midlength version of the CASV-M shown above with a few differences. Like the CASV-M, the CASV-S is designed to be used with a midlength gas system with any front sight/gas block, or with a carbine (or shorter) gas system with low profile gas block underneath.

Bi-level rail - The CASV-S shares the same aluminum construction as the EL and M, and attachment/installation method. The main difference between the CASV-S and the EL and M versions is that it has a bi-level top rail. In other words, the rear portion is the same as the EL and M versions, then the rail drops down forward of the receiver to the same height as the receiver flat top. This allows the use of any rail-mounted front sight on the front portion of the rail with a low-profile gas block on the barrel. It is not compatible with the folding front sight of the CASV-M. The top half of the handguard has been reduced in height to accomodate the lower rail, while the bottom portion remains the same height. This results in a lower-profile feeling rail. Width is the same as the other CASV versions.

The main features of the CASV-S are as follows:

• Same attachment to the top rail as the EL and M models.
• Bi-level top rail - the front portion is at the same height as the flat top.
• For use with midlength or carbine gas systems. With a midlength, the gas block will be exposed. With a carbine, it will be under the rail (as shown on the rifle below). Most low profile gas blocks like the Vltor, will fit underneath the handguard.
• Threaded inserts on the sides, bottom, and upper/lower 45° surfaces for more rail mounting options.
• Available only in black at the present time.

The CASV-S is illustrated below on the rifle with a low profile gas block and MI folding front sight mounted on the front of the bi-level rail. At the time of this writing, the CASV-S is still not available, but will be soon. Please contact Vltor directly for more information on the release date.

Black CASV-S

Bottom view

10/28/06 - Daniel Defense, Inc. is the Savannah, Georgia manufacturer of parts and accessories for the AR15 and AR10 weapons systems. DD is well known for many of their products, including the Burnsed Loop receiver end plate for sling attachments and also their handguard/rail systems, some of which are the lightest available at the time of this writing. There are currently two variants of DD free float rails; the M4 Rails which attach using the 'Thread Ring Mounting System', and the Lite rails which utilize the patent pending 'Bolt Up' system. Shown here is the Lite Rail 12.0, which as the name implies is a 12" rifle length rail. It's the lightest free float rail with a steel barrel nut, weighing 14.0 oz complete (rail and mounting components).

DD rail handguards are machined from 6061-T6 aluminum and finished with a black Mil-Spec type III hard anodize. Indexing marks/'T-numbers' are laser engraved on all the Mil-Spec 1913 rails. The quality of machining and finishing is top notch. Width across the rails is approx 2" and height is 2.4". The handguard is symmetrical in cross section, with the top and bottom rails the same height/distance from the boreline. The Lite 12.0 is heavily ventilated with lightening holes, to which the light weight can partly be attributed to. A sleeve which provides the six-bolt interface fits into the rear of the rail and is welded in place. The rail free floats off the barrel nut. Since the bolt-up system doesn't utilize a threaded nut to secure the rail to the barrel nut, the top of the rail extends back to the receiver, for an uninterrupted/'monolithic' look.

Parts - The DD Lite rail 12.0 arrives neatly packaged and includes a new proprietary steel barrel nut, bolt-up plate, hardware, and three santoprene ladder rail covers. The steel barrel nut replaces the standard barrel nut and has four slots which accept a proprietary stamped-steel wrench. That's my only gripe about the Lite rail - it needs a special wrench to be installed that's purchased separately. That's fine if you're a gunsmith or build up multiple uppers to make it more cost effective, but it'd be nice to have it included in the package so it's not an additional cost/separate purchase as the DD Lite rails are at the higher end of the price range already. Hopefully DD can come up with an alternate, less expensive solution. The bolt up plate is a ring that has six holes which interface with the rear of the rail, and serves as the mounting clamp to the barrel nut when the rail is attached and the bolts are tightened.

Installation (see 5th photo from left, below) - The barrel nut wrench is pictured in (1). The bolt up plate is placed on the receiver extension (2), making sure the gas tube hole lines up with the one in the receiver and the barrel is installed to the receiver. The barrel nut is then slid over the barrel (3), and tightened with the proprietary barrel nut wrench (4). You can obtain the proper torque with this setup since you're not trying to line up the barrel nut with the gas tube hole. Very easy and quick. There is no anti-rotation feature, but a rail loosening up should not be an issue when correctly installed/torqued.
The rail is then placed over the barrel and bolted up to the bolt up plate. The gas block has to be installed after the rail, as it will not pass through the rear opening. If a rifle length gas system is used with the 12.0 rail, the gas block will extend beyond the front of the rail and can be installed after the rail is bolted up completely. Since I had an intermediate gas system (read more below), the gas block was covered by the rail, which blocked access to the set screws at the bottom of the gas block. Luckily, the rail has holes at the bottom, so I left the rail loosely bolted up with a couple of bolts, lined up the holes, and tightened the set screws. I then proceeded to install the rest of the bolts. The bottom two screws install from the muzzle end, and the others from the receiver end. When I first tried to install the bottom screws, I thought they went in from the rear, as I hadn't read the printed instructions nor looked at any photos. When they didn't fit, I thought that they just weren't compatible with the Vltor MUR receiver I was using. If I had actually read the included instructions before starting, like they recommended, I'd have known that. When I finally read the instructions and realized my dumb mistake, I corrected it and installed the rest of the bolts. I also used a spare ACOG mount to keep the rail and flat top aligned while I tightened the bolts. I just put it across the top, straddling the receiver and rail and kept it snug. I tightened the bolts in a cross-sequence manner.

Daniel Defense Lite Rail 12.0 components

Front and rear quarter views

Cross section

Mounting components

Installation

Bolt-up plate

Holding the rail in place with spare ACOG mount

The handguard feels rock solid and looks really nice with this build, in which I used the Vltor MUR 1-S (no forward assist) and a Vltor SPR barrel. I installed the TangoDown ACB-4 bipod and the legs tucked up perfectly into the bolt-up interface (see right pic).

Front view

Top view of interface

Assembled rifle

TangoDown bipod installed

At the range with Nightforce scope

Vltor Intermediate gas system SPR barrel preview and Low Profile Gas Blocks - The barrel I used for the DD Lite build is an experimental Vltor SPR barrel. Vltor had only two of these Vltor-marked made. It's an 18.5" stainless steel barrel with 1/7 twist, with an intermediate gas system. The intermediate length system is longer than a midlength, and shorter than a rifle length system. It's actually 1.5" shorter than a rifle length system and utilizes an intermediate length gas tube. This enables the gas block to be protected just inside a rifle-length rail (see above). The profile is proprietary to Vltor, but it has a continuous taper to maximize accuracy and minimize weight, and is contoured at the front to accept the OPS Inc 12th Model MBS suppressor shoulder/collar for the SPR MK 12. The two experimental barrels were made by Compass Lake Engineering (CLE) for Vltor from a Douglas Premium stainless steel barrel blank and came with a matching headspaced bolt. Continuing this project, Vltor collaborated with Noveske Rifle Works and this design is now available as Noveske's SPR barrel group.

Vltor also manufactures low profile steel gas blocks, both in bead blasted stainless finish and parkerized. Noveske is currently using Vltor gas blocks for their barrels. The gas blocks come in clamp and set screw versions. The set screw version is meant to be used under rails/handguards, like the DD Lite build above. They've got grooves machined into the sides for cosmetic appeal and the Vltor sword logo engraved on the front. Very nice indeed.

Vltor SPR barrel

Sword logo

Muzzle

Extension

Vltor low-profile gas blocks

Gas block mounted

Barrel assembled to MUR

10/14/06 - LaRue Tactical has not only made a name for themselves with their excellent locking-lever mounts, but also their free-float handguard/rail systems. The rails are available in five different lengths (total length of the handguard) - including carbine, midlength, rifle length and some variations. Featured here are the 7.0 (carbine) and 12.0 (rifle) models. The 7.0 weighs 11.2 oz and the 12.0 weighs 16.2 oz.

The handguards are machined from 6061 aluminum extrusions and mil-spec hard coat anodized matte black for a lasting finish. The threaded rear ring portion is machined as a separate piece, then mechanically joined to the handguard part using a proprietary system and also sealed with aerospace adhesive to eliminate the chance of any moisture from flowing between the joints. The first thing I noticed was that they felt slim. Taking some rough measurements, I measured the rails to be 2.0" across and 2.2" in height (same as the LMT MRP) - less than all the other rail systems including the KAC RIS and Troy. I do like the feel of a slimmer handguard as I've got small hands and a narrower rail is easier for me to get my hands around, especially with rail panels. There's always that compromise between radiated heat from a hot barrel and comfort (the closer to the barrel the hotter it can get), but the LaRue handguards are extensively ventilated to allow airflow. The rails have laser engraved "T-numbered" positions, and also the KAC panel 'cuts' at each end which enable the KAC panel clip to snap in place.

Parts - The components that make up a LaRue handguard are the handguard/rail, handguard nut, barrel nut, spacer, anti-rotation device/keeper and hardware. The photo on the right show how the components go together. (1) Shows the rear of the handguard with the two stainless steel pins which align the handguard to the barrel nut. (2) The spacer slips over these pins and the keeper bolts screw into the spacer when finally installed. (3) The stainless pins interface with the holes in the barrel nut and prevent the handguard from rotating. (4) The handguard nut pulls the handguard rearward into the barrel nut and tightens it all up. The keeper is grooved, and when the two bolts are tightened down, prevent the handguard nut from rotating. The front of the upper receiver sits in the channel in the keeper, and prevents the whole assembly from rotating.

Installation - The handguard, being essentially one-piece tubes, requires the removal of the front sight base for installation. Once that is done, the standard barrel nut can be removed, along with the delta ring assembly - none of those parts are needed. The handguard nut is first slipped over the end of the barrel, along with the barrel nut. The keeper is placed on the upper receiver and the barrel nut snugged down by hand until a barrel wrench is needed. Using a barrel wrench, the barrel nut is tightened and loosened three times, then torqued so the gas tube hole lines up properly. The spacer is then installed in the rear of the handguard which is slipped over the front of the barrel and the handguard nut tightened and snugged up with a strap wrench. The keeper screws are installed and this locks down the handguard nut and prevents it, and the whole assembly from rotating. The gas tube/front sight base is then re-installed. The same procedure applies to all the LaRue handguards.

12.0 and 7.0 front quarter view

Rear quarter view

Handguard components

Rail cross section

How the parts go together

Installed, the handguard feels completely solid, with no movement whatsoever. A really nice touch is the sling swivel insert at the rear of the rail, which accepts Uncle Mike's sling swivels. That's where I attach the front of a 2-pt sling, like the BFG VCAS. The great thing about it is that the insert limits the rotation of the swivel, so the sling doesn't twist. Looking at the side profile, the top of the handguard rail is at the same height as the receiver flattop. The bottom rail is slightly higher (closer to the barrel) than some others, contributing to the slim overall feel of the handguard, which is preferable to me with TangoDown panels installed.

Anti-rotation plate

Sling swivel mount

Side profile

LaRue 7.0 on carbine

LaRue 12.0 upper build - see Stealth Precision Upper build above.

9/4/06 - I had an early (maybe 10 years old?) Bushmaster V-match upper that I had almost forgotten about and thought needed updating. The receiver wasn't even a real flattop - it had a weaver mount screwed onto the top of the upper receiver with the carry handle machined off. The round aluminum FF tube also looked outdated and was limited in what I could attach to it. I had a spare flattop receiver sitting around, and looked at my options for a rifle-length free float rail. I didn't want KAC or Troy Industries as I already have uppers with those products, so I decided to give the Midwest Industries, Inc rail a try as I'd heard good things about them, and am familiar with their well-made sling adapters. MI makes both free float and non-free float forearms in a variety of lengths. The non free float rails simply replace the factory handguards - no alteration to the host weapon needed. The free float forearms require that the delta ring be removed. This can be done by dremeling it off without having to remove the front sight base. The V-match had no delta ring, so I had to take off the front sight base anyway.

The MCTAR-22 arrived well protected in a stiff cardboard tube. My first impression was that it was a nicely made, quality item. The hard-coat anodizing was even, and a deep matte black. Laser-etched T-numbering was crisp on all four rails. I also noticed that it felt wider than my other handguards. The outside measurement across rails was about 2.45", compared to 2.2" for the KAC RIS and Troy Ind MRF-C, which are narrower across than they are in height. The MCTAR-22 is the same measurement in width as it is in height. I asked Troy at MI about this, and he explained that the free float handguards are made from the same extrusion as the non-free float handguards, and use common sized rings for attachment to the host weapon. By having one sized symmetrical handguard instead of two, the savings are passed on to the customer, and that's reflected in the affordability of MI's forearms. Although I'd like as narrow a profile as possible, the upside to a wider forearm is that the rails are further from the hot barrel. The MCTAR-22 also has a lot of ventilation with large holes and a gap between the upper and lower assemblies.

The main components are the upper and lower rails, a barrel clamp and a front C-shaped ring. The upper rail has the top half of the barrel clamp already installed, held in by 4 screws. It slips over the barrel nut, and the bottom clamp is installed with four bolts and tightened. There aren't any 'anti-rotation' ears that index the upper receiver, and personally I'd like to see some added to the top half of the barrel clamp (for a warm fuzzy feeling). But as long as the barrel nut is torqued properly, there shouldn't be a problem with it loosening and rotating. The front C-ring is then installed to the upper rail. The bottom rail is then attached at the front C-ring, and with a screw at the rear. The entire process takes less than 5 minutes, if you've already got the delta ring off.

MCTAR-22 components

Side view of attachment

Barrel nut clamp

Clamp installed

Front ring

MCTAR-22 bottom view

Since the MCTAR-22 was a bit wider, I dug out my old KAC rail panels which are thinner than TangoDown ones I normally prefer. The MI rails have the cutouts for the KAC panel latches to engage, located at the front, rear and midway down the rail. When I slid a KAC panel all the way to the rear, the latch wouldn't engage. The barrel clamp prevents the panel from going far back enough for the latch to engage. It's a quick and easy fix, though - the user can solve it by cutting off the portion of the tab behind the KAC panel that interferes (which is what I did). It's just a 0.15" plastic tab at the end that I broke of with a pair of needlenose pliers that doesn't affect the rail whatsoever, and that took less than a minute to do for both panels. The latches now engage and the panels are locked on the rails.

Side view, installed

With TD bipod installed

With KAC Panels

After handling the rifle with the MCTAR-22, I found that the extra width is a non-issue - it feels just fine. The TD ACB bipod does have to be mounted so the feet clear the rear of the rail, and the legs fold up nicely along the rail. The MCTAR-22 (and other MI freefloats) is definitely worth considering as it's a quality item at a very affordable price.

1/20/07 - The MCTAR-17 2-piece Carbine Forearm from Midwest Industries, Inc is a very reasonably priced option for the shooter who wants a rail system for his carbine, but doesn't want to alter the host weapon, or require gunsmithing. It's also M203 or shotgun compatible with the bottom rail removed.

The MCTAR-17 is made from the same size extrusion as the MCTAR-22 free float handguard reviewed above, and shares the same cross-section: outside measurement across rails was about 2.45" - same height and width. The other features are also shared - crisp T-numbering on all four Picatinny rails and large holes for ventilation. The forearm has two pieces; the upper and lower half. At the front of the forearm are semi-circular rings which slip into the front handguard retaining cap. At the rear are rings which are grooved to fit around the barrel nut, and secured by the delta ring.

Installation is as easy as replacing the standard plastic handguards. Pull back on the delta ring and remove the plastic handguards. Install the MCTAR-17 top and bottom halves how you'd normally install the plastic handguards; first the front, then the back, ensuring that the barrel nut sits in the grooves. The delta ring locks the forearms in place securely - I could not feel any movement whatsoever.

MCTAR-17 components

Inside the forearm

Installed

Top rail level with receiver

The top of the MCTAR-17 is at the same level as the flat top receiver. The rails also have the cutouts at each end for installing KAC panels. Since the MCTAR-17 is slightly wider than some other rails, the ladder-type rail covers that MI also sells work well while adding the least amount of width.

Right side

Left

6/16/04 - Here is the Troy Industries MRF (Modular Rail Forend) carbine length. Mid length and rifle versions are also available using the same attachment method. I'd have to say that the quality of the machining and finish is excellent. Cuts are crisp (these rails aren't tumbled, it looks like), and the finish is a deep, matte black. Any sheen in the pics is due to oil. It's constructed of 6061-T6 aluminum. The MRF's main components are a top rail, lower rail, and barrel nut clamp. The portion between the rails is longitudinally fluted/grooved - the additional surface area might serve to dissipate heat more quickly. The top rail lines up perfectly with the flattop receiver rail. Overall, a very attractive and well made piece. The MRF-C weighs 11.6oz. For comparison, a KAC FF carbine rail weighs 11.4oz, the RAS II is 13.8oz, DD 7.0 is 8.5oz and ARMS SIR #50 is 16.1oz.

The forend came with clear, illustrated instructions which were a breeze to follow. Installing the forend first requires removal of the delta ring components - delta ring, spring and c-ring. These can be cut off with a dremel or slid off after removing the front sight base. The top rail is then installed over the top half of the barrel nut, and the clamp installed on the lower half. The clamp has two anti-rotation tabs on either side which center it on the lower sides of the upper receiver. This prevents rotation of the upper rail or barrel nut (which it clamps to) relative to the receiver. The fit of the tabs to the receiver depends on which end of the tolerance the receiver was made at. Any play (if any) will be very small. Just as a secondary measure the ensure that the top rail was perfectly aligned to the flat top rail, I used a spare weaver rail mount to bridge the two rails and tightened it down, clamping them in line with each other. Before installing the lower clamp, a stainless steel detent and spring is placed into the detent hole, which later serves to lock the lower rail in place. 4 screws secure the lower clamp to the upper rail and when these are tightened, the rail system is locked on place. All parts went together without a hitch - this was a very simple installation. The lower rail/handguard has tabs that slide into corresponding slots in the top rail. The tabs are lined up, and the rail is slid back until the spring loaded detent locks it in place. I could feel absolutely no movement of the lower rail, either fore/aft, or side/side. To remove the rail, the detent is pressed and the lower rail slides forward and off. The forend does not touch the handguard cap, there is a very small gap there - it is completely free floating.

The upper and lower mil-std 1913 rails are clearly T-numbered in sharp, white characters. Width of the forend looks to be the same as the KAC RIS (approx 2.2" wide across rails). The top rail is the same height, of course, but the bottom one is approx .15" lower than the KAC.

The clamp area does pose an issue - since the bottoms of the side rails stop at the clamp, rail panels will go no farther aft. Even though there are cutouts for Knight's rail panel clips on the first and last slots, a full-length KAC rail panel's clip will not engage. The panel is too long for the clip to engage in the front, and unless the panel is relieved, the clamp does not provide the necessary clearance to engage the clip on the aft slot. Short KAC rail panels will only engage the front slots. The Tango Down rail panel clip will not engage in the front, but can be installed with the clip to the rear. The clamp area, however, will be bare (much like a delta ring or barrel nut on a free-floating forend. I decided to relieve my Tango Down rail panels to cover that area, as I sometimes use a mag well hold instead of the vertical grip. I used a dremel to relieve the necessary amount (first pic, below). The panel now insulates my hand from the clamp area, which is likely to get hot. The Tango Down vertical grip was a solid fit - no side-side movement whatsoever.

Other than that rail panel fitting issue which I promptly fixed - I'm very pleased with the MRF-C. I replaced the KAC RIS that I had on this upper (which now resides on my MARPAT carbine), and it looks good.

Initial review 1/4/04 - Another entry into the rail market is SureFire's M73 rail system. Priced below most other rails, it's worth looking at for those who want a good value.

Initially advertised as a 'free-floating' handguard, it most definitely isn't. The bottom rail bears on the barrel nut while the top rail has setscrews that push against the bottom rail, effectively lengthening the rail system and wedging it in between the handguard cap and barrel nut. It's sturdy when attached, yes, but I personally don't like the mode of attachment. Why? It puts non-uniform pressure on the barrel by pushing forward at the top of the handguard cap and at the bottom at the barrel nut.

The rail covers/ladders that come with it are similar to the 'ladder covers' offered by another company. Why the top rail isn't at the same level as the flat top is a mystery to me (I've been told that it's for lower profile mounting of laser devices on top of the rail - makes sense to me now). The price of this system (under $180) is the big attraction, for those who don't want/need a free floating handguard/rail.

Revised review 2/2/05 - When I first got the rail in Jan 2004, the finish and quality wasn't up to par, and I was disappointed, being used to the excellent quality of SureFire's lights. So my initial review was unfavourable. Someone whose opinion I trust brought it to my attention that he had different observations with his M73, which had none of the QC issues I brought up in the above writeup, and liked the rail. This is from someone who has BTDT. I did that writeup when the first run of M73's came out, and since then I have been given a new M73 rail, and have to agree that the quality of manufacturing HAS improved and they look much better than the sample that I had (which could have been a pre-production sample). I won't retract my previous observations (as they still stand for that sample), but wanted to update the writeup to reflect that the production rail has improved since I did my writeup, and the finish and quality of manufacturing is as good as any of the other mil-std rails on the market (see the pics of the current production rail below.). I'm still not fond of the way it attaches, but that's nitpicking from an engineering standpoint and probably has no practical consequence. That being said, the M73 does look to be a better value than I had originally thought, and a good alternative to the more expensive RIS/RAS. It's also one of the easiest rails to install, and no modification to the host weapon is necessary.

Bottom rail (L) and top rail (R)

Heat shields

Front set screws

Rear attach point and bi-level top rail

Mounted on a rifle