AR-15, AR-10, AR-9 and Glock parts compatibility
Pick your platform, then match the one thing that matters on it.
AR-15 and AR-10 receivers never mix. Inside each platform it comes down to one spec: caliber on an AR-15, receiver pattern on an AR-10, magazine pattern on an AR-9, and model and generation on a Glock. The AR builders flag a part that does not fit the moment you add it.
AR-15: most mil-spec parts fit
A mil-spec AR-15 lower takes almost any AR-15 upper. What has to match is the caliber: the barrel, bolt and magazine all have to suit the same round.
Our builder checks
- AR-15 or AR-10 frame size
- Caliber across upper, barrel and bolt
- Gas tube to barrel gas length
- Muzzle device to barrel thread
- Handguard mount
You check
- Wobble between an upper and lower from different makers
- Older Colt lowers with the large front pin
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.
Older Colt AR-15 lowers use a front pivot pin about .065 inch bigger than most other brands' upper pivot holes, so a standard upper needs a two piece threaded adapter pin to fit one.
AR-10: match the pattern, not just the size
AR-10 has no single standard. A DPMS pattern upper and an ArmaLite pattern lower do not go together, and even two DPMS pattern parts from different makers can need fitting.
| Spec | DPMS (LR-308) | ArmaLite |
|---|---|---|
| Where the receivers meet | Curved cut, like an AR-15 | Sharp angular cut |
| Barrel nut thread | 1-7/16 inch, 16 TPI | 1-7/16 inch, 18 TPI |
| Who uses it | Most AR-10 parts on the market | ArmaLite, LMT, Knight's Armament |
Our builder checks
- AR-15 or AR-10 frame size
- Receiver pattern on each listing
- Lower and upper from different makers (flagged)
- Muzzle device to barrel thread
- Gas tube to barrel gas length
You check
- Pin sizes between makers on the same pattern
- Magazines: not every .308 mag fits every lower
You can shimmy an Armalite upper onto a DPMS lower and get it to run, but the gaps between the receivers make it potentially dangerous.
AR-10 takedown and pivot pin sizes vary slightly between receiver makers even on the same pattern, so check with both makers before mixing brands.
AR-9: match the magazine
A 9mm AR runs Glock or Colt style magazines, and the lower and the bolt have to be cut for the same one. It is blowback, so it has no gas system and wants a heavier buffer.
Our builder checks
- Glock or Colt magazine pattern on the lower and the bolt
- Gas parts a 9mm does not use
- Muzzle device to barrel thread
You check
- Buffer weight
- Last round bolt hold open
9mm ARs run either Colt style metal stick mags or Glock pistol mags, and each one needs its own bolt and mag well design.
Blowback 9mm ARs cycle only on the cartridge's recoil, so they need heavier buffers than the 3.5 to 6 oz typical of AR buffers.
Glock: match the model and generation
Glock slides, barrels and frame parts are made for a model and a generation. Our Glock builder prices every part, but it does not check fit yet, so read the model and generation on each listing.
Check on each listing
- Model (17, 19, 43X and so on)
- Generation
- Optic cut on the slide
Common questions
Will an AR-10 upper fit an AR-15 lower?
No. A .308 AR-10 upper can't be used on an AR-15 lower because the lower is too small for the .308 cartridge.
Do DPMS and ArmaLite pattern AR-10 receivers fit each other?
No. DPMS and Armalite pattern AR-10 receivers do not fit each other because the geometry doesn't match, and most AR-10 parts on the market follow the DPMS pattern.
Do AR-15 parts work in an AR-10?
Some do. AR-15 triggers, pistol grips, buffer tubes, stocks and safeties work in an AR-10, but the bolt catch, mag catch, buffer, buffer spring and takedown pins do not.
Can a 9mm upper go on a standard AR-15 lower?
Some can. CMMG's radial delayed blowback 9mm upper drops onto a standard AR-15 lower and feeds from CMMG's 9mm mags or inserts that go in 5.56 PMAG bodies.
Can I use Glock magazines in an AR-9?
Yes, with a Glock pattern lower and bolt. Aero's EPC-9 lower takes standard frame Glock 17 and 19 pattern mags, and a 7.7 oz buffer is recommended for the EPC.
Does a .300 BLK upper work on an AR-15 lower?
Yes. .300 BLK uses standard 5.56 mags and parts except the barrel, so a barrel swap converts an AR-15.
Will a 6.5 Grendel upper fit my AR-15 lower?
Yes, with Grendel mags. Alexander Arms' 6.5 Grendel and .50 Beowulf uppers fit any standard spec AR-15 lower, but those rounds won't feed reliably from .223 mags.
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.