M16 - Monolithic Rail Platform

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M16 - Monolithic Rail Platform
« em: Outubro 23, 2004, 01:10:23 pm »
Text and Photos By Gary Paul Johnson
Soldier of Fortune Magazine

Lewis Machine & Tool (LMT) Monolithic Rail Platform

Killer Features:
Revolutionary .45-auto cartridge that fits into the 9mm/.40-caliber magazine envelope
Performance of .45-auto cartridge is equal to .45 ACP ammunition
Accuracy of 3 inches or less at 25 yards
Accessory frame-rail accepts M3 Tactical Illuminator from Insight Technologies, as well as SureFire's new X200 Tactical Light

They said it couldn't be done -- even I said it couldn't be done. When asked for my opinion a few years ago during the USSOCOM's search for a quick-change barrel system for the M4 Carbine, my answer was that the M16 already has a quick-change barrel capability.

To change the barrel on any M16 or AR-15, simply push out both receiver pins, remove the upper receiver group and replace it with one having a new barrel, or a different barrel configuration. This component comes pre-headspaced and can be already sighted in. SOCOM decided to do just that, not because I said so, but because others also shared that view.

Changing the upper receiver group on the M16 is as valid today as it has always been, and the practice is in wide use throughout the world. My main point in refuting the possibility of quickly changing the barrel of the M16 was that the configuration of the M16's aluminum upper receiver and gas tube arrangement simply didn't lend itself to a quick-change system, but I was thinking inside the box.
Mr. Carl Lewis, owner of Lewis Machine & Tool (LMT), rarely thinks inside the box, and conceived of a method for a quick-change M16 barrel several years ago. After extensive experimentation and development, LMT has released the system, but it doesn't stop there, not by a long shot.

Called the Monolithic Rail Platform (MRP), LMT's new system appears far more conventional than it is. Beginning life as a 2'X4"X4" 7075 aluminum alloy forging, the 8 pound billet is placed in a CNC mill where 95 percent of it is machined away. What remains is a one-piece upper receiver with an integral forend. On this integral forend are four M1913 rails, the top one running uninterrupted from the rear of the upper receiver to the front of the forend. The other three rails are located on both sides and the bottom of the forend. Hence the term, Monolithic Rail Platform.

In order to accommodate a variety of mission-specific needs, two forend lengths are offered. One is a longer rifle version and another intended for use with carbine or CQB length barrels, all of which can be removed and replaced in about two minutes. However, the differences in forend lengths don't necessarily require the barrels intended to be used with them. This is because the barrels are essentially independent of the forend and are totally free floating. For example, the 18" rifle barrel can easily be used in the short "carbine" MRP, but will protrude more. The same is true with the 14.5" barrel being used in the longer MRP, and even the 10" CQB barrel could be installed in the longer MRP if necessary.
Four barrel-lengths are currently offered for the MRP including 10", 14.5", 16" and 18". While the three shorter barrels use the short gas tube, the 18" uses a bas block positioned mid-length on the barrel, or about 2" farther forward of the short gas block, and about 2" to the rear of the standard gas block on the 20" barrel M16 rifle.

The term gas block is especially appropriate for the MRP, as it is only a gas block and not a front sight base as on the M16/AR-15 rifles. The MRP's gas block also differs in that it uses a perfectly straight gas tube rather than the curved one of the M16, and so the front end rides higher in the gas block. Forward of the barrel extension is a rigid positioner that holds the gas tube in line with its portal in the upper receiver, during installation. As for open sights, they are mounted atop the rail, as are any variety or combination of optical sights.

Boasting a one-piece receiver/forend, the Lewis Machine & Tool Carbine/CQB and Rifle Monolithic Rail Platforms also use the first successful quick-change barrel system for the M16. Both the Carbine (top) and fulllength MRP’s are seen here with a spare 14.5” barrel.

The secret of the MRP’s quick-change barrel system is the two TORX bolts seen forward of the dust cover along with a TORX head wrench.


Did I forget to mention accessories? Having four M1913 Mil-Spec rails offers an unlimited platform on which to mount optics, sights, lights and more. Measuring the MRP's rails revealed that they were right on the money, and mounting A.R.M.S. ThrowLevers on the rails confirmed it. If a rail isn't MilStd M1913, an A.R.M.S. ThrowLever will either not clamp, or will be too loose. This is because Mr. Richard Swan, of A.R.M.S. designed the rail standardized as the M1913 (sometimes erroneously referred to as the "Picatinny" rail).

Using A.R.M.S. ThrowLever Rings, I not only mounted the Leupold MR/T, but also the Leupold Close Quarter/Tactical (CQ/T) the Aimpoint Comp ML2, Eotech, Trijicon's Tri-Power and 4X ACOG, and the Meprolight Reflex Sight. I also mounted a SufrFire MD Tactical Weapon Light using an A.R.M.S. ThrowLever Mount with a Falcon Industries vertical foregrip and a SureFire M900 Tactical Light, and I mounted a Harris Bipod with an A.R.M.S. ThrowLever Adapter.

More proof that the MRP rails are MilStd is that Dark Parts handguard panels from Excalibur Arms fit them perfectly. These unique panels were designed by David Luke, formerly a systems analyst with Knight's Mfg. Co. For a more slender forend where heat is not a problem, Falcon Industries' Low Profile handguards fit just as well. What's more, heat is not a problem with the MRP, as the barrel remains totally free floating and touches no part of the forend.

Although LMT's open sights are in development as this is written, I borrowed a set of pre-production flip-up sights from ArmaLite and mounted them on the MRP Carbine upper receiver as can be seen in the accompanying photos.

Barrels In About Two Minutes

Although LMT's "MRP" is its namesake, the heart of system is its quick-change barrel. Utterly simple, this capability is also just about foolproof. All one needs is an inch-pound torque wrench. At the front of the upper receiver above and forward of the front hinge the receiver is reinforced, and along the middle of the bottom it is slotted. Through the side of this reinforced section are two holes that accept two hardened Torx-head bolts. On the right side where the bolts enter are recesses for their heads and on the left side two steel nuts are recessed.

The front Torx-head bolt passes through both the upper receiver and a rounded notch in the bottom of the barrel extension, and the rear bolt passes through the receiver just beneath the barrel extension. With the barrel in place both bolts are tightened to 90 inch-pounds. Both bolts draw the slotted section of the receiver together for a few thousandths of an inch to rigidly tighten the barrel extension in the receiver, and the front bolt locks the barrel from moving forward.

To remove/change the barrel, first put the safety ON, then remove the magazine, make sure the chamber is empty and lock the bolt to the rear. Now loosen the rear Torx-Head bolt and remove the front bolt from the receiver. Then simply pull the barrel from the receiver and forend and replace it with another. Although the barrel extension is a close fit in the loosened receiver, it and its gas tube can easily be slid into place. Now replace both bolts and tighten to 90 inch- pounds each and, presto, you've installed a new barrel in about two minutes.
Although I used a standard inch-pound adjustable torque wrench, LMT should have a wrench set to break at 90 inch-pounds available by the time you read this. Operating much like the gas cap on your vehicle, this simple wrench will tighten only to 90 inch pounds and then ratchet, but will loosen the bolt even if it is tighter.

The quick-change barrel capability is, in my opinion, the MRP's best-kept secret and is of much greater value than the monolithic rail itself. Even more important is its ability to return to and retain zero. Removing and replacing the same barrel will duplicate the point of impact, and replacing one barrel with another of the same configuration will move point of impact no more than about 0.5". Changing to a barrel of different length can result in a slight change in elevation due to the difference in velocity.

 Each MRP barrel comes with its own gas tube mounted. Shown here are the 18”, 14.5” and 10” barrels and the two upper receiver MRP’s tested.

 Trigger Time

In addition to all of the above optics and accessories, the MRP's were tested with lower receiver groups fitted with the REDI-MAG from Boonie Packer Products and both the Magpul Ind. buttstock used by the USMC, and also the VLTOR ModStock with its spare battery tubes. The carbine version of the MRP was also used with Boonie Packer's excellent new two-Point Sling, the simplest tactical sling I've yet used.

Using high quality Match Grade .223 Remington caliber ammunition, both upper receiver groups produced accuracy of 1 MOA or better, with the 18" heavy barrel shooting the best groups. All accuracy tests were conducted using Leupold's new Mid-Range/Tactical (MR/T) 30mm scope. Identical to Leupold's TS-30A2 Sniper Scope made especially for the USSOCOM's Special Purpose Rifle (SPR) used in the Global War On Terrorism (GWOT), the MR/T is a 3-9X40mm scope with an illuminated mil-dot reticle. The only difference is that it is designated MR/T instead of TS-30A2. This scope was mounted in a set of A.R.M.S. 30mm ThrowLever Rings also standard on the SPR.

Changing between the 14.5" barrel and the 10" CQB barrel in the carbine MRP naturally produced some difference in elevation, but windage stayed inside of one inch. This repeatability can be summed up in two words - QUALITY CONTROL, two words that have come to be synonymous with Lewis Machine & Tool. This is the reason so many companies who have suddenly entered the AR-15 style rifle business are quick to point out that their rifles are made for them by LMT Ð smart thinking.

In testing the two MRP components on selective-fire lower receiver groups, we experienced no malfunctions in either semi-automatic or full-automatic fire using several brands of ammunition. Notable, however, was that while the short barrels /gas systems produced a rate of fire of about 750 rpm, the 18" barrel with its mid-length gas system ran at about 500 rpm. During this testing, Global Tactical Supply's LULA 30-round Magazine Bench Loader proved quite valuable in saving time and fingers. Just drop 28 or 30 rounds of .223 ammunition into the tray, slide the loading block and presto, the magazine is fully loaded.

The Future

To say that LMT's MRP is of the highest quality is to put it mildly, but its intended purpose remains open. To the professional, the answer is obvious. It makes as much sense as having a quick-change barrel on any weapon. Not only does the MRP have mission-specific capabilities, but its quality control also makes it fully workable in terms of accuracy and reliability. For example, a precision rifleman could practice with a used barrel, replace it with his new one, fire verification rounds for group and go back to work.

What about variations of the system? The MRP seen here is in full production and, while I can't comment on other possibilities at present, don't be surprised if you see different versions of the system offered in the future. In terms of caliber, as this is written, the MRP is only available in .223, but by the time you read this LMT should also be offering the system in 6.8mm Remington SPC, a caliber that is increasingly being requested by the military in the Global War On Terrorism (GWOT). There's a good argument to have a quick-change barrel system for the M16 and it also satisfies one of the requirements of the Special Operations Forces Combat Assault Rifle (SOFCAR, formerly SCAR) program.

The full-length MRP (top) has the Leupold MR/T Scope and Harris Bipod mounted with A.R.M.S. mounts, and Dark Parts Handguard Panels. The Carbine MRP has the 10” barrel with a SureFire M900 Tactical Weapon Light, the new desert tan VLTOR ModStock, and Falcon ERGO Grip and Low Profile Handguards in the same color. Both magazines also use Magpul protectors.

Este post é dedicado ao Luso, é uma tentativa de aumentar o meu mérito junto dele depois das minhas bocas em relação ao Fê Cê Pê :lol: