https://en.wikipedia.org/wiki/List_of_AR_platform_calibersAR-15 calibers
Rimfire calibers
.17 Mach 2
.17 HMR[1]
.17 Winchester Super Magnum[1]
.22 Long Rifle[2]
.22 Winchester Magnum Rimfire[1]
Centerfire calibers inch measurement
.17 Mach IV
.17 Remington Fireball
.17 Remington[1]
.17-223[3]
.20 Practical[4]
.204 Ruger[1]
.222 Remington
.223 Remington - Original AR-15 caliber: .223 cartridges may function in a 5.56×45mm rifle, however 5.56×45mm cartridges can produce excessive pressure in a .223 rifle. On the other hand, a .223 Wylde chamber is used on .223 caliber rifle barrels to allow them to safely fire either .223 Remington or 5.56x45mm NATO ammunition.[5]
.22 PPC
.22 Nosler
.224 Valkyrie
.224 Kritzeck (Shortened .223 remington neck) [6]
.223 Winchester Super Short Magnum[5]
.243 LBC[7]
.243 Winchester Super Short Magnum[5]
.25 Winchester Super Short Magnum[5]
.25-45 Sharps
.277 Wolverine (6.8×39mm)
.30 Carbine[1]
.30 Remington AR[8]
30 American[9]
300 OSSM[5]
300 AAC Blackout (7.62×35mm)[8]
.300 Whisper[8]
.350 Legend[10]
358 Yeti - Wildcat [11]
375 SOCOM
.40 S&W[12]
.45 ACP[13]
.450 Bushmaster[1]
.458 SOCOM[14]
.50 Action Express
.50 Beowulf[15]
Centerfire calibers metric measurement
5.45×39mm[1]
5.56×45mm NATO - Original AR-15A2 caliber: can also safely fire .223 Remington[1]
FN 5.7×28mm
6×45mm
6.5mm Grendel[1]
6.8×39mm (.277 Wolverine)[16][17]
6.8mm Remington SPC[8]
7.62×37mm Musang
7.62×39mm[8]
7.62×40mm Wilson Tactical[8]
7.92x33mm Kurz
9mm Parabellum[2]
10mm Auto[13]
9x39mm[18]
Calibers which will not feed but which are used in rifles where the receiver functions only as a trigger group
.338 Lapua Magnum
.408 CheyTac
.50 BMG