Do Smith & Wesson lowers fit CMMG uppers?
Smith & Wesson lower + CMMG upper: yes, they fit
Yes. Smith & Wesson AR-15 lowers fit CMMG AR-15 uppers. 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. We checked them with the rules the AR builder runs.
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 Smith & Wesson M&P15 Lower with the CMMG Resolute 16.10in Upper.
About 1 in 50 Smith & Wesson lowers in our builds carries a CMMG upper.
Smith & Wesson's M&P15 is the entry point AR a lot of people start with, sold as complete rifles and complete lowers.
Founded 1852, Maryville, Tennessee
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
Smith & Wesson lowers and CMMG uppers 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-15: yes, they fit
Both are AR-15 size receivers. An AR-15 lower takes the upper's 5.56 NATO.
Checked on this Smith & Wesson lower
Smith & Wesson M&P15 Lower 5.56x45mm/.223 Remington$269.99and this CMMG upper
CMMG Resolute 16.10" Upper 5.56x45mm$403.20Most built Smith & Wesson lowers and CMMG uppers setups
Ranked by how often builders pick the exact pair. Only pairs our rules pass are listed.
#1Yes, they fit57% of these buildsCheck fit
#2Yes, they fit11% of these buildsCheck fit
#3Yes, they fit7% of these buildsCheck fit
#4Yes, they fit4% of these buildsCheck fit
#5Yes, they fit4% of these buildsCheck fit
#6Yes, they fit4% of these buildsCheck fit
#7Yes, they fit4% of these buildsCheck fit
#8Yes, they fit4% of these buildsCheck fit
What Smith & Wesson and CMMG say
Smith & Wesson: The S&W M&P15 Sport II lower has a rounded winter trigger guard forged in one piece with the receiver, not the usual separate guard.
Smith & Wesson: The S&W M&P15 stripped lower fits M&P15 and AR-15 builds in .223, 5.56, 300 Blackout and 300 Whisper.
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.
CMMG: CMMG does not guarantee its DISSENT runs right with mil-spec or other aftermarket triggers.
CMMG: American Rifleman reported that CMMG's 5.7 AR Conversion magazine fits a standard AR-15 magazine well and works with CMMG's 5.7x28 upper, and CMMG recommends a standard carbine buffer and action spring.
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 Smith & Wesson lowers
- Smith & Wesson lowers + BCM uppersMost picked
- Smith & Wesson lowers + PSA uppersSecond most picked
- Smith & Wesson lowers + Daniel Defense uppersThird most picked
- Smith & Wesson lowers + Geissele uppersFourth most picked
- Smith & Wesson lowers + TacFire uppersFifth most picked
- Smith & Wesson lowers + Aero uppersSeventh most picked
Other lowers under CMMG uppers
- CMMG lowers + CMMG uppersMost picked
- PSA lowers + CMMG uppersSecond most picked
- Aero lowers + CMMG uppersThird most picked
- Wilson Combat lowers + CMMG uppersFifth most picked
Smith & Wesson lowers and CMMG uppers: questions builders ask
Will a CMMG upper fit a Smith & Wesson lower?
Yes. Smith & Wesson AR-15 lowers fit CMMG AR-15 uppers. Both are AR-15 size receivers.
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.
Why might a CMMG upper feel loose or tight on a Smith & Wesson 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.