Do CMMG lowers and uppers fit together?

CMMG lower + upper: yes, they fit

Yes. CMMG AR-15 lowers and uppers fit together. Both are AR-15 size receivers. A real mil-spec keeps AR-15 receivers from different makers close, though not exact, and fit problems show up most when the upper and lower come from different makers. Their AR-10 (.308) and AR-9 (9mm) lowers and uppers fit each other too.

One exception: CMMG AR-15 lowers are a smaller frame and do not fit CMMG AR-10 (.308) uppers.

Fit comes from the same rules the AR builder runs on every part you add. Build data only ranks the setups; it never decides fit. Checked November 10, 2026.

Our take

Most built setup: the CMMG MK3 Semi-automatic Stripped lower with the CMMG MK3 .308 Stripped upper.

CMMG is the most picked upper brand on CMMG lowers.

CMMG

CMMG makes complete AR rifles, pistols and parts, and it's known for Radial Delayed Blowback, its action for pistol caliber ARs in rounds like 10mm and .45 ACP.

Founded 2002, Boonville, Missouri, Made in USA

CMMG lowers and lowers by platform

Each row is checked on the most built part of that platform from each brand.

Platform	Fit
AR-15	Yes, they fit
AR-10 (.308)	Yes, they fit
AR-9 (9mm)	Yes, they fit
AR-15 lower + AR-10 (.308) upper	No, they do not fit

AR-15: yes, they fit

Both are AR-15 size receivers. The upper is stripped, so the barrel you pick sets the caliber.

Checked on this CMMG lower

CMMG MK4 .223 Remington AR Lower$100.02

and this CMMG lower

CMMG MK/4 Upper Receiver Armor$130.55

AR-10 (.308): yes, they fit

The lower is DPMS Gen 1 (LR-308) and the upper is DPMS high profile, the same AR-10 receiver family. An AR-10 (.308) lower takes the upper's .308 Win.

Checked on this CMMG lower

CMMG MK3 Semi-automatic Stripped Lower Receiver 308$204.99

and this CMMG lower

CMMG MK3 Banshee Upper Receiver Group .308 Winchester$840.30

AR-9 (9mm): yes, they fit

Both are AR-9 receivers. A 9mm lower takes the upper's 9mm.

Checked on this CMMG lower

CMMG MK9 Stripped Lower 9mm$149.33

and this CMMG lower

CMMG Banshee 9mm Upper$716.63, out of stock

AR-15 lower + AR-10 (.308) upper: no, they do not fit

The lower receiver (.223 Wylde / 5.56 NATO / Multi) cannot support a AR-10/.308 build.

Checked on this CMMG lower

CMMG MK4 .223 Remington AR Lower$100.02

and this CMMG lower

CMMG MK3 Banshee Upper Receiver Group .308 Winchester$840.30

Most built CMMG lowers and lowers setups

Ranked by how often builders pick the exact pair. Only pairs our rules pass are listed.

#1Yes, they fit6% of these buildsCheck fit
CMMG MK3 Semi-automatic Stripped Lower Receiver 308$204.99 CMMG MK3 .308 Stripped Upper Receiver w/o Forward Assist$324.95, out of stock
#2Yes, they fit4% of these buildsCheck fit
CMMG MK4 .223 Remington AR Lower$100.02 CMMG Resolute 16.10" Upper 5.56x45mm$403.20
#3Yes, they fit4% of these buildsCheck fit
CMMG MK4 .223 Remington AR Lower$100.02 CMMG MK/4 Upper Receiver Armor$130.55
#4Yes, they fit4% of these buildsCheck fit
CMMG MK4/ Stripped Lower Receiver Tungsten$97.95 CMMG MK4/ Upper Receiver Tungsten$139.99, out of stock
#5Yes, they fit3% of these buildsCheck fit
CMMG MK4/ Stripped Lower Receiver$174.95 CMMG MK4/ Forward Assist Upper Receiver Armor$115.27, out of stock
#6Yes, they fit3% of these buildsCheck fit
CMMG MK4 .223 Remington AR Lower$100.02 CMMG Resolute MK4 6mm ARC Upper$682.74
#7Yes, they fit3% of these buildsCheck fit
CMMG MK4 .223 Remington AR Lower$100.02 CMMG MK4/ Forward Assist Upper Receiver Armor$115.27, out of stock
#8Yes, they fit3% of these buildsCheck fit
CMMG MK3 Semi-automatic Stripped Lower Receiver 308$204.99 CMMG MK3$279.99, out of stock

What CMMG says

CMMG: CMMG's MkGs lower takes 9mm or .40 S&W Glock and SGM magazines and is meant for CMMG MkGs Radial Delayed Blowback uppers only.

CMMG: CMMG's MkG lower takes Glock and SGM .45 ACP magazines and is made for CMMG .45 ACP Radial Delayed Blowback uppers, and other brands' uppers may work but are not guaranteed.

CMMG: A CMMG DISSENT upper fits most of CMMG's BANSHEE, RESOLUTE and ENDEAVOR lowers only after you pull the buffer tube and stock and install the adapter plate that comes with the upper.

Check your exact parts Start a build All brand pairs

Fit is judged from the specs retailers list, which can be missing or wrong. Confirm with the manufacturer before you buy, and have a qualified gunsmith check any build before you fire it.

Other uppers builders put on CMMG lowers

CMMG lowers + Aero uppersSecond most picked
CMMG lowers + TacFire uppersThird most picked
CMMG lowers + BCM uppersFourth most picked
CMMG lowers + PSA uppersFifth most picked

Other lowers under CMMG uppers

PSA lowers + CMMG uppersSecond most picked
Aero lowers + CMMG uppersThird most picked
Smith & Wesson lowers + CMMG uppersFourth most picked
Wilson Combat lowers + CMMG uppersFifth most picked

CMMG lowers and uppers: questions builders ask

Do I need a matched upper and lower?

A real mil-spec keeps AR-15 receivers from different makers close, though not exact, and fit problems show up most when the upper and lower come from different makers.

Does a CMMG AR-10 lower fit a CMMG upper?

CMMG AR-10 (.308) lowers and uppers fit together. The lower is DPMS Gen 1 (LR-308) and the upper is DPMS high profile, the same AR-10 receiver family. CMMG AR-15 lowers are a smaller frame and do not fit CMMG AR-10 (.308) uppers.

Why might a CMMG upper feel loose or tight on a CMMG lower?

Some play between an AR-15 upper and lower is common, but it can get excessive when the two come from different makers, and a tension screw or an Accu-Wedge takes it up.