CMMG AR-15 MK4 Receiver Extension KIT
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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.
Specifications
Available Merchants(8)
Prices checked
Price Alert
September 2026 on GunPartPicker
CMMG AR-15 MK4 Receiver Extension KIT was the ninth most added buffer tube on GunPartPicker in September 2026, behind the VLTOR Weapon Systems A5 Receiver Extension Tube, with about 2% of all buffer tubes added to builds. That's its 2nd straight month at #9. Builds with this buffer tube are mostly chambered in 5.56 NATO (72%, then .223 Wylde 9%), split between mid-length (40%) and carbine-length (31%) gas systems, and nearly all AR-15.
Availability is good: it was in stock at one retailer or another nearly every day in September 2026, and today 4 of the 8 retailers we track have it in stock. It dipped to $29.69 at BattleHawk Armory for a stretch in September 2026, under its usual $30.99 to $36.49, so sales do come around. Buying today, the lowest price is $36.49 at Ammunition Depot, above September's low of $29.69, so a better deal may come back.
Updated · from real builds on GunPartPicker · Prices checked · refreshed daily across 37 retailers
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Frequently Built With
The part most often added in each category by the builds that include this one
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CMMG AR-15 Mil-Spec Trigger KIT
CMMG AR15 Ambi Mag Catch, Black - 55AFF6E
TPS Arms AR-15 Safety Selector, Black - AR1033
Magpul MOE K2 Grip Polymer Gray
CMMG AR-15 HD Pivot and Takedown Pin Parts KIT - 55AFF3B
Build Configuration Breakdown
Aggregated and anonymized data showing how builders use this product
PlatformBased on real build data showing which platform (AR-15, AR-10, AR-9) builders pair with this product.
CaliberBased on real build data showing which calibers builders choose alongside this product.
Gas SystemBased on real build data showing which gas system lengths builders use with this product.
Builds Featuring This Part
See all 5 →Builds in the community that include the Cmmg Ar-15 Mk4 Receiver Extension Kit
| Build | Parts | Total |
|---|---|---|
 | 29 | $1851.11 |
 | 19 | $689.84 |
 | 24 | $872.60 |
 | 24 | $1074.67 |
 | 17 | $1723.43 |
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