I’ve had the pleasure of handling one of Lewis Machine and Tool’s Monolithic Rail Platform upper receivers for the AR-15/M-16 pattern rifles. At first glance it doesn’t look like there’s anything to set the MRP apart from any other flat top upper receiver with a railed free float tube for the AR. A careful examination will prove this wrong; unlike other upper receivers with free float tubes, the MRP is all one piece. Rather than having a separate upper receiver and a free float tube, the MRP is milled from one massive aluminum forging and incorporates a unique patent pending method for quickly changing the barrel.

With the MRP I can quickly change between 11.5”, 14.5”, 16”, and 18” barrels. Naturally, unless the lower reciever is registered as a SBR (Short Barrelled Receiver) or is registered as a machinegun, the 11.5” and 14.5” barrels would be illegal. Naturally one wouldn’t change barrels in the heat of combat or a match, but it gives the user the unique ability to tailor the weapon to the mission at hand.

End users have reported a less than .5 MOA difference when the barrel is removed and replaced, and when compared to the 1 MOA difference generally allowed for removable optics mounts.

Inside the MRP, “M-4” feed ramps have been milled into the barrel extension to aid feeding should the weapon be fired full auto; it’s just more insurance for those of us who are limited to semi auto fire.

Above: Side profile from the right side of the rifle. Rail panels are by Tangodown LLC for LMT. Optic is a Trijicon TA-31A ACOG mounted in an ARMS #19S quick release base. Eventually the base will be replaced with a LaRue ACOG base. Back Up Iron Sights (BUIS) will be from Troy Industries and will be added as finances allow.

If you look closely, you’ll notice the carbine length rail panels do not completely cover the rails. This is because the MRP is what is termed “Mid Length” meaning that the gas block is two inches farther forward than would be on a regular AR carbine or M-4. This supposedly aids in reliablity; I think it makes the rifle look more balanced with the 16” barrel.

This is a closeup of the forward part of the free float tube and shows the extra real estate the mid-length rails offer as well as the custom designed gas block LMT uses for the MRP.

This is a closeup view of the right side of the receiver showing the two torx screws that hold the barrel and tighten the forward extension of the receiver to stabilize and secure the barrel. The front screw is tightened to 90 inch pounds and the rear to 80 inch pounds.

This is a closeup of the bottom of the upper receiver extension showing how the two bolts secure the sides and secure the barrel.

This is a closeup of the left side of the receiver showing the steel inserts the bolts screw into to secure the barrel.

This is a photo of the M-4 feed ramps that are part of the barrel extension. These ramps aid in feeding and help prevent jams.

The MRP and lower receiver produced by Lewis Machine And Tool are of the highest quality in fit and finish and in the future I hope to add more to my collection.

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