BCM MK2 Receiver Extension for AR-15
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Threads into AR-15/M4 lower receivers with a standard threaded rear, and per Bravo Company USA is usable on most AR-10 platforms. Suits UK straight-pull AR-15 builds. Tube only: requires an MK2-specific buffer and an M16 rifle action spring. A carbine buffer and carbine action spring will not function in it. Castle nut, end plate and stock not included.
Not sure it fits your rifle? Ask us before you order
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.
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.
| Platform | AR-15 / M4; usable on most AR-10 platforms |
|---|---|
| Fits | Lower receivers with a standard threaded rear; Mil-Spec stocks from USGI, BCM, Colt, LMT, SOPMOD, VLTOR, Stag Arms |
| Type | Intermediate-length receiver extension, tube only — requires an MK2 buffer and an M16 rifle action spring |
| Material | 7075-T6 aluminium |
| Finish | Hard coat anodised, Mil-A-8625F Type III Class 2 |
| Adjustment | 8 stock positions |
| Brand | Bravo Company USA |
| MPN | BCM-MK2-RE |
Buy the tube, but buy the right buffer and spring with it. Order the BCM MK2 Receiver Extension today — imported from the USA with all duties paid by us and dispatched tracked from the UK in 7–10 business days, with nothing to pay on delivery.
Explore more: AR-15 Parts & Accessories, Rifle & Shotgun Stocks or browse all Bravo Company USA.
| Platform | AR-15 / M4; usable on most AR-10 platforms |
|---|---|
| Fits | Lower receivers with a standard threaded rear; Mil-Spec stocks from USGI, BCM, Colt, LMT, SOPMOD, VLTOR, Stag Arms |
| Type | Intermediate-length receiver extension, tube only — requires an MK2 buffer and an M16 rifle action spring |
| Material | 7075-T6 aluminium |
| Finish | Hard coat anodised, Mil-A-8625F Type III Class 2 |
| Adjustment | 8 stock positions |
| Brand | Bravo Company USA |
| MPN | BCM-MK2-RE |
| Category | Lower Parts |
| Barcode | 812526023599 |
£5 tracked UK delivery on every order via Royal Mail Tracked 24. Our products are ordered in from the manufacturer rather than held in UK stock, so please allow 7 to 10 business days (Monday to Friday, excluding bank holidays) from the date of your order for it to reach you. Tracking details are emailed on dispatch. UK delivery only.
You have 30 days from receiving your order to cancel it for any reason, then 14 days to send it back unused and in its original packaging. Faulty, damaged or incorrect items are replaced or refunded and we cover reasonable return postage. Refunds go back to your original payment method within 14 days of receiving the return.
No. This is the single most important thing to know about the MK2. It is an intermediate-length receiver extension and it requires an MK2-specific buffer together with an M16 rifle-length action spring. A carbine buffer and carbine action spring will not function in it. Fit the wrong parts and the rifle will not work.
The tube on its own. There is no buffer, no action spring, no castle nut, no end plate and no stock. If you want the whole assembly matched from the factory, the BCM MK2 Recoil Mitigation System supplies the tube, buffer, rifle action spring, castle nut and QD end plate together — both it and the separate MK2 buffers are in our <a href="/collections/bravo-company-usa">Bravo Company USA</a> range.
Mil-Spec dimension stocks, including USGI, BCM, Colt, LMT, SOPMOD, VLTOR and Stag Arms. The sliding surface is cut slightly smaller than a plain Mil-Spec tube, which is deliberate: it takes the wobble out of the stock rather than making it incompatible.
Yes, and the correct buffer and spring matter just as much there. The tube houses the buffer and action spring that return the carrier after you cycle the rifle by hand, so the assembly still has to be correctly specified.
Parts are sent from the United Kingdom with £5 tracked UK delivery in 7–10 business days, and tracking is emailed to you when the parcel ships. If a part turns out to be the wrong fit, see our returns policy or <a href="/pages/contact">contact us</a> and we'll help sort it.
7 to 10 business days from the date of your order. Every order is sent Royal Mail Tracked for a flat £5 and you receive tracking details by email when it is dispatched.
Yes. We list only genuine parts and optics from the brands shown, ordered in from the manufacturer for your order.
Compatibility notes on this page come from the manufacturer. If you are unsure, email us with your make and model before ordering and we will check rather than guess.
Yes. Bundle & Save applies automatically in your basket: 5% off when you buy 2 items, 10% off at 3 items and 15% off at 4 or more. It works across the whole range, so you can mix and match, and there is no code to enter.
Yes — you have 30 days from delivery to cancel for any reason, as long as the item is unused and in its original packaging. See our returns policy for the details.
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