BCM MK2 Receiver Extension for AR-15

The BCM MK2 Receiver Extension is an 8-position intermediate-length buffer tube for AR-15 and M4 rifles, supplied as a bare tube with no buffer, no action spring and no stock.

A carbine buffer and a carbine action spring will not work in this tube. The MK2 requires an MK2-specific buffer and an M16 rifle-length action spring, and there is no way around that.

This is the point people get wrong, so it is worth being blunt about it. The MK2 is an intermediate-length receiver extension: longer than a carbine tube, and designed around a longer spring and a purpose-made buffer. Dropping in the carbine buffer and carbine spring from your existing build will not give you a working rifle. You need a BCM MK2 buffer and an M16 rifle action spring to go with it. If you would rather buy the tube, buffer, spring, castle nut and end plate as one matched set, the BCM MK2 Recoil Mitigation System Mod 1 does exactly that; and if the MK2 tube is already in the rifle and you only need the buffer itself, that is the BCM MK2 Buffer Mod 1.

With the correct parts in it, the MK2 is a well-made tube: machined from 7075-T6 aluminium, hard coat anodised to Mil-A-8625F Type III Class 2, cut to Mil-Spec dimensions but with a slightly smaller dimension where the stock slides on, which is what removes the stock wobble that plagues ordinary tubes. The interior is given a dry lube spray coating. It offers eight stock positions rather than the usual six.

Why shooters choose the BCM MK2 Receiver Extension

• Eight positions — finer length-of-pull adjustment than a six-position carbine tube
• Tightened stock interface — a slightly smaller sliding dimension takes out stock wobble
• 7075-T6, hard coat anodised — Mil-A-8625F Type III Class 2
• Dry lube interior coating — applied from the factory
• Takes standard Mil-Spec stocks — USGI, BCM, Colt, LMT, SOPMOD, VLTOR and Stag Arms

What the BCM MK2 Receiver Extension fits

Threads into AR-15/M4-pattern lower receivers with a standard threaded rear, and Bravo Company USA state it is usable on most AR-10 platforms as well. It suits UK straight-pull AR-15 builds, where the buffer and spring return the carrier after every hand-cycled stroke, which is precisely why the correct spring and buffer matter. It takes Mil-Spec dimension stocks from USGI, BCM, Colt, LMT, SOPMOD, VLTOR and Stag Arms. Supplied as a tube only. You must add an MK2 buffer and an M16 rifle action spring — a carbine buffer and carbine spring will not function in it — and the castle nut, end plate and stock are also not included. Fitting needs a castle-nut wrench, and the nut should be torqued and staked or thread-locked.

Specifications

Buy the tube, but buy the right buffer and spring with it. Order the BCM MK2 Receiver Extension today — in stock at Xtreme Tactical Gun Parts with free tracked UK delivery in 7–10 days.

Explore more: AR-15 Parts & Accessories, Rifle & Shotgun Stocks or browse all Bravo Company USA.