CMMG MK4 receiver extension kit includes the buffer tube, spring, castle nut, and end plate. Adjustment lever locks tight at each position. Six positions. Threads to a standard milspec castle nut. Complete kit at a reasonable price.



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CMMG
Overview
The CMMG AR-15 Mk4 Receiver Extension Kit is a comprehensive parts kit designed for building a carbine-style AR-15. This kit includes a Mil-Spec buffer tube that ensures compatibility with various components, providing reliable function and performance in your build. It is commonly found in carbine gas system builds chambered in 5.56 NATO, making it a solid choice for standard AR-15 configurations.
Based on build data

CMMG AR-15 HD Pivot and Takedown Pin Parts Kit - 55AFF3B

CMMG AR-15 Carbine Buffer Assembly - 55CA977

Strike Industries Flat Wire Spring for AR Carbine - AR-FWS-C

CMMG AR15 Ambi Mag Catch, Black - 55AFF6E

Fortis Lightweight Enhanced AR-15 End Plate, Gold - LE-BLK-K1-GOLD

Wilson Combat Ar-15 Lower Receiver Forged
Aggregated and anonymized data showing how builders use this product
| Product | Category | Times Built Together |
|---|---|---|
| CMMG AR-15 HD Pivot and Takedown Pin Parts Kit - 55AFF3B | 24 | |
| CMMG AR-15 Carbine Buffer Assembly - 55CA977 | 21 | |
| Strike Industries Flat Wire Spring for AR Carbine - AR-FWS-C | 15 | |
| CMMG AR15 Ambi Mag Catch, Black - 55AFF6E | 12 | |
| Fortis Lightweight Enhanced AR-15 End Plate, Gold - LE-BLK-K1-GOLD | 11 | |
| Wilson Combat Ar-15 Lower Receiver Forged | 9 |
| Platform | Percentage |
|---|---|
| AR-15 | 100% |
Builds in the community that include the Cmmg Ar-15 Mk4 Receiver Extension Kit
| Build | Parts | Total |
|---|---|---|
![]() | 29 | $1720.82 |
![]() | 19 | $653.37 |
![]() | 24 | $933.80 |
![]() | 24 | $1211.07 |
![]() | 17 | $1575.36 |
1 global rating
CMMG MK4 receiver extension kit includes the buffer tube, spring, castle nut, and end plate. Adjustment lever locks tight at each position. Six positions. Threads to a standard milspec castle nut. Complete kit at a reasonable price.