LMT’s Monolithic Rail Platform
At SHOT Show 2004, a new black rifle was introduced that was not just a copy of the standard design that most of the industry produce. This black rifle would move the family of weapons into new uncharted territory. Karl Lewis, president of Lewis Machine & Tool (LMT) introduced the MRP, the monolithic rail platform.
The MRP is the first monolithic upper receiver. The upper receiver is machined from a single 7075 T6 aircraft aluminum forging. There are four solid Mil-Std 1913 rails and permit complete zero retention for optics or any other accessory placed on the rails. The upper receiver is equipped with a forward assist, fired cartridge case deflector as well as an ejection port dust cover. All rails are numbered for easy replacement of optics to insure they are placed back in the same position from which they were removed. Removable sling swivel mounts are placed on the end of the MRP at the 3, 6 and 12 o’clock positions. Additionally, mounting points are located on the right and left side at the rear of the handguard area by the ejection port. This permits any type of sling or desired location for the operator’s discretion.
The innovation does not stop with the development of the first one piece monolithic rail platform. The barrel, held in by two bolts, is removable by the user. When the bolts are removed the barrel/gas tube assembly is pulled straight out of the receiver. This enables the 5.56mm caliber weapon to be configured for whatever mission it will be used. If a close quarter combat environment is the mission, a 10.5 inch barrel may be used. If the mission is urban or normal combat ranges, a 14.5 or 16 inch barrel may be used. If longer range is required, an 18 or 20 inch barrel may be used. It should be noted the 16 inch 5.56mm barrel uses a mid-length gas system and all others use a standard carbine gas system. All is accomplished at the user level; no armorer is needed to change out the barrels. The barrels are manufactured from machine gun barrel steel and button cut rifling. They are cut with the Mil-Spec 1 turn in 7 inch twist allowing up to 80 grain projectiles to be stabilized. The barrels have chrome plated bore and chambers and are equipped with an A2-style compensator. With Lewis Machine & Tool being a U.S. government contractor for many different parts, they are familiar with what Mil-Spec means and what it takes to achieve it. All barrels manufactured by Lewis Machine & Tool are proof tested with a 70,000 psi proof cartridge and then magnetic particle inspected to insure the barrels are free of stress fractures. When the barrel is installed in the MRP, the barrel is completely free floating. This increases accuracy as well as the air holes in the MRP circulate air to aid in cooling. The removable barrels also enable another innovation: the MRP is a multi-caliber weapon as different caliber barrels can be used. Complete changing of the barrel is accomplished in less than 5 minutes.
The MRP provided for this evaluation came with many enhancements that are all Karl Lewis. Starting with the sights, the rifle was provided with the LMT BUIS (Back Up Iron Sight). This is a fully adjustable rear sight that has been provided to the U.S. Navy and SOCCOM for the MK18 CQB 10.3 inch carbines. The sight is identical to that of the standard M16A2 or M4. The front sight is removable and held on by a nut. It has the traditional triangular shape and square front sight post. Of course, being a Mil-Std 1913 rail, any BUIS can be mounted.
The charging handle has an improved latch that is easier for one to grasp as it is made wider so it is easier to actuate.
The bolt and carrier are also a significant departure from the norm. When Lewis looked at the new design, he looked at the specific operating dynamics of the carbine and how different it is from the rifle. Given the different dynamics, Lewis designed the bolt and carrier to function with that in mind. To begin with, the bolt carrier has had several modifications. Due to the dynamics of the carbine, the bolt unlocks at a faster rate on a carbine length gas system than a full length rifle. Owing to this quicker action, there is still residual pressure in the cartridge case and it is still somewhat expanded when the rifle starts to extract making the extractor and extractor spring work that much harder to extract that cartridge case. It also causes extractor springs to wear quicker than that of the rifle. SOCOM has added rubber O-rings to increase the extractor force to cope with the wear issue. The standard GI M4 has a new and improved extractor spring (copper in color) that is designed specifically for the carbine to increase extractor force. Lewis also redesigned the geometry of the cam track by increasing the dwell time upon unlocking and thus permitting additional time for the residual pressure to drop allowing much easier cartridge extraction. He also added an additional gas relief port to get rid of unneeded gas.
The bolt was also redesigned with durability on mind using proprietary material that is significantly stronger than standard bolt material. Due to its hardness it is more expensive to procure and more expensive to machine than standard bolt steel. The geometry of the locking lugs has been modified as well. There are stress relief cuts that allow more flexing of the lugs to prevent breakage. The extractor has been redesigned as well. The improved “lobster tail” extractor uses two extractor springs instead of one that significantly enhances the reliability of the extractor in adverse conditions. The extractor claw is considerably more aggressive and stronger as well. Like the barrels and as per Mil-Spec, all LMT bolts are proof tested and them magnetic particle inspected.
The lower receiver has many enhancements as well. The stock is the LMT SOPMOD stock and is the stock assembly purchased by USSOCOM and the U.S. Navy for the M4A1 carbines and the MK18 CQB weapons. The stock is triangular in shape and very smooth. There are two removable sling mounting points on the stock as well as a cut-out for a standard GI silent sling. There are two battery compartments that are water resistant tubes placed inside of the stock and there is a removable rubber butt plate as well. The receiver extension is also designed by LMT and has six positions as opposed to the standard M4 which has 4 positions. The provided pistol grip is the Ergo Grip that is extremely comfortable and with the finger grooves is comfortable and makes the rifle stable in the shooting hand in adverse conditions. Also provided on the lower receiver is the Ergo Grip Gapper. This little spacer covers the gap in-between the front of the pistol grip and the trigger guard. LMT’s proprietary ambidextrous selector lever is also provided. This is not just good for left handed shooters but can be just as useful to right handed shooters as well given the tactical situation. Tangodown rail covers were provided on the rails.
The rifle was outfitted with the new EOTech XPS2-2 two dot reticle holographic sight. Extremely compact, this sight uses a single 123 battery and has a battery life is 500 to 600 hours. This sight only requires 2.75 inches of rail space. Along with the sight is the EOTech Generation II 3X magnifier. This comes with a Samson Quickflip tilting mount attached to an A.R.M.S. throw lever mount. When disengaged, the magnifier sits to the right side of the rifle: when engaged for long range shooting it flips back.
Also attached to the rifle was the Insight Tech M3X tactical light with pressure pad activation that was mounted in a Tangodown vertical foregrip. By just removing a spacer, the pressure pad sits in the grip. The grip also is hollow allowing for additional storage.
The magazines chosen for the rifle are the Magpul PMag, one of the finest magazines available anywhere in the world for the Black Rifle. This magazine is a significant reliability enhancement to any member of this family of weapons. The constant curve design allows the shot column to sit in its natural shape and increase feed reliability.
The ammunition for this test was provided by Silver State Armory (SSA). SSA is known for manufacturing some of the highest quality duty and match ammunition in the industry at competitive pricing. Silver State Armory just moved to a state-of-the-art facility in Packwood, Washington where they have a 100 meter underground range and the facility meets United States Department of Defense requirements to manufacture military contract ammunition. They manufacture their own brass. All SSA ammunition is loaded with custom blends of powder geared towards the specific loading. They offer several loadings in 5.56mm, 7.62mm NATO, 6.8SPC and .499 LWRC. They are also one of the only ammunition manufacturers in the United States to manufacture armor piercing rifle ammunition in 5.56mm, 7.62mm NATO and 6.8SPC.
More than 300 rounds of SSA 5.56mm 55gr FMJ rounds were fired through the MRP for function testing and no malfunctions were encountered. There were 200 rounds of SSA 5.56mm 77 grain OTM cartridges fired as well. Groups at 100 yards kept around 1.75 inch groups consistently with the FMJ rounds. All in all, this barrel has had more than 500 rounds through it and as it has broken in the groups had tightened up. First groups fired with the SSA 5.56mm 77 grain OTM were consistent at 1.75 inches. The last groups fired with this ammunition were printing consistently at 1 MOA.