The BCM MK2 Recoil Mitigation System Mod 1 is a complete buffer system for AR-15 and M4 rifles, supplying the MK2 buffer, an M16A4 rifle action spring, the MK2 receiver extension, a castle nut and a QD end plate in one kit.
This is the complete system, not a component. Five parts ship together: the MK2 Mod 1 buffer at your chosen weight; a Mil-Spec M16A4 rifle action spring with more coils than an M4 carbine spring; the MK2 receiver extension, 7075-T6, 8-position, Mil-Spec diameter and approximately ¾" longer than a carbine tube; an M4 castle nut; and a receiver QD end plate with an integral QD swivel mount. If you only want the buffer — because the MK2 tube is already in the rifle — the bare component is the MK2 Buffer Mod 1, which is the same buffer on its own.
The engineering is in the pairing. The intermediate-length tube gives the buffer more room, the buffer runs a longer internal counterweight travel with an internal spring to quiet it, and the longer rifle spring with its extra coils widens the operating envelope and steadies carrier velocity. Together they reduce bolt bounce and give a more consistent return to battery. It is covered by BCM US Patent 10415907.
The three weights let you tune the system: T0 at 3.8 oz (110 g) is the lightest stroke, T2 at 5.6 oz (160 g) the most deliberate. The QD end plate in the kit also gives you a sling point at the rear of the receiver without buying one separately.
Key Features
- Complete five-part kit — buffer, rifle spring, MK2 receiver extension, castle nut and QD end plate
- Intermediate-length tube — approximately ¾" longer than carbine, giving the buffer more travel
- M16A4 rifle action spring — more coils than an M4 carbine spring for a wider operating envelope
- Three buffer weights — T0 3.8 oz (110 g), T1 4.7 oz (135 g), T2 5.6 oz (160 g)
- QD end plate included — a rear sling point comes with the kit rather than as an extra
Compatibility & Fitment
Fits AR-15/M4 lower receivers that take a Mil-Spec-diameter receiver extension, and replaces the existing tube, spring, buffer, castle nut and end plate entirely. One fitment caveat matters: because the MK2 extension is approximately ¾" longer than a carbine tube, some Mil-Spec stocks will not collapse all the way back to the castle nut — the stock still works, it simply will not close fully. Commercial-diameter tubes are a different specification and are not what this kit supplies. The buffer, spring and tube in this kit are designed as a set: do not mix the MK2 buffer with a carbine spring or a carbine tube, as BCM states that incompatible combinations can damage the rifle and injure the operator.
What's Included
- MK2 Mod 1 buffer in your chosen weight (T0, T1 or T2)
- Mil-Spec M16A4 rifle action spring
- MK2 receiver extension — 7075-T6, 8-position, Mil-Spec diameter
- M4 castle nut
- Receiver QD end plate with integral QD swivel mount
Technical Specifications
Platform | AR-15 / M4 |
Fits | AR-15 / M4 lower receivers taking a Mil-Spec-diameter receiver extension |
Type | Complete recoil system — MK2 buffer, M16A4 rifle action spring, MK2 receiver extension, castle nut and QD end plate |
Material | Buffer 7075-T6 aluminum; MK2 receiver extension 7075-T6 aluminum |
Finish | Hard-coat anodized |
Weight | Buffer T0 3.8 oz (110 g) · T1 4.7 oz (135 g) · T2 5.6 oz (160 g) |
Length | MK2 receiver extension approximately ¾" (19 mm) longer than a carbine extension |
Adjustment | 8-position receiver extension |
Brand | Bravo Company USA |
US Shipping & Support
Shipped from D&R Sports Center in the USA with fast, tracked delivery. Questions on fit, mounting or which model suits your setup? Our team is glad to help before and after your purchase.
Frequently Asked Questions
What exactly is in the box?
Five parts: the MK2 Mod 1 buffer in your chosen weight, a Mil-Spec M16A4 rifle action spring, the MK2 receiver extension (7075-T6, 8-position, Mil-Spec diameter), an M4 castle nut, and a receiver QD end plate with a QD swivel mount. A stock is not included — you fit your existing stock to the new tube.
How is this different from the MK2 Buffer Mod 1?
The MK2 Buffer Mod 1 is the bare buffer on its own, for shooters who already run an MK2 receiver extension and want to change weight or replace a part. This listing is the complete system and includes that same buffer plus the tube, spring, castle nut and end plate. Same T-numbers, very different contents — if you are converting a standard carbine rifle, this is the one you want.
Which buffer weight should I choose?
T0 is 3.8 oz (110 g), T1 is 4.7 oz (135 g) and T2 is 5.6 oz (160 g). More mass means a more deliberate stroke and more resistance to bolt bounce; less mass means a lighter, quicker stroke.
Will my stock still fit and still collapse?
Your stock fits, because the MK2 extension is Mil-Spec diameter and 8-position. It may not collapse completely: the tube is roughly ¾" longer than a carbine extension, so some Mil-Spec stocks stop short of the castle nut at the closed position. Everything else about the stock works normally.
