Ever wonder why the AR-15 is such a great platform? The modularity in chamberings and calibers is amazing! Some require a new barrel, bolt, mags, upper, etc, but you can squeeze a ton of different calibers out of an AR-15.

Here’s a partial listing. This list is in no way complete as many new cartridges are made. If someone can figure out how to shove the round through the magwell or slap the upper on, it is made for AR-15’s! This list also does not account for complete uppers like the FN 5.7×28, .410 shotgun, crossbow bolts, golf ball launchers or bolt action uppers like the .338 Lapua, 50BMG, etc.

Standard Mil-Spec Bolt
.17 Remington
.17/223
.20 Tactical
.20 Practical
.20 Vartag
.204 Ruger
.221 Fireball
.222 Remington
.222 Remington Magnum
.223 Remington
.223 Remington Ackley Improved
6x45mm
6mm TCU
6x47mm
6mm Whisper
.25x45mm
6.5mm Whisper
7mm Whisper
7mm TCU
.300 Whisper (.300/221, .300 Fireball)
.300 AAC Blackout
.338 Whisper
5.56x45mm NATO

With Bolt Modification
20 LBC
22 LBC
243 LBC
264 LBC
223 WSSM
5.45x39mm (.21 Genghis)
243 WSSM
6mm PPC
6mm WOA
6mm BR Remington
6mm Hagar
6MM Turbo
6 BR
6 BRX
6X6.8
6.5mm PPC
6.5 WSSM
6.5 WOA
6.5mm Grendel
25 WSSM
6.8x43mm SPC
6.8 SPCII
.30 Herrett Rimless Tactical
7.62×25
7.62x39mm
.30 RAR
300 OSSM
.357 Auto
.35 Gremlin
.358 WSSM
.458 SOCOM
.50 Action Express
.50 Beowulf

Blowback Operation
.17 HMR
.17 HM2
.22 LR
.22 WMR
9x19mm
9×21
9×23
30 Carbine
357 Sig
40S&W
400 Cor-Bon
41 Action Express
10mm Auto
45 ACP
45 GAP
45 Super
45 Win Mag

…and MANY more…