Here is a good list of what can be on an actual AR15 lower. All of these you could buy a parts set for the lower and buy an upper with this chamber. Any other round would not be an actual AR15. It would just eb an AR style rifle and most parts would not fit it.

AR-15, without bolt modification
.17 Remington
.20 Tactical
.204 Ruger
.221 Fireball
.222 Remington
.222 Remington Magnum
.223 Remington (5.56x45mm)
.223 Remington Ackley Improved
6x45mm
6mm Whisper
6.5mm Whisper
7mm Whisper
7mm TCU
.300 Whisper (.300/221, .300 Fireball)
.338 Whisper

AR-15, with bolt modification
223 WSSM
5.45x39mm (.21 Genghis)
243 WSSM
6mm PPC
6mm BR Remington
6.5mm PPC
6.5mm Grendel
25 WSSM
6.8x43mm SPC
.30 Herrett Rimless Tactical (6.8x43mm case trimmed to 41mm and necked up to .308; the 6.8mm version of the .300 Whisper)
7.62x39mm
.357 Auto
.458 SOCOM
.50 Action Express
.50 Beowulf

AR-15 using a simple blowback operation
.17 HMR
.22 LR
.22 WMR
9x19mm
40S&W
10mm Auto
45ACP