5.56mm
the standard m16 shoots the 5.56mm, but it can be converted to shoot 9mm, 7.62mm, even .308
.308
Depends mostly 3 round burst though can be fully aoutomatic mos accurate with da 3 round burst
In the 1960's there was the Gyrojet gun which were actually miniature rockets but the caliber was larger than the .223 round of the M16
Noop. an M16 fires a 5.56mm (or .223 caliber) bullet. A .45 caliber shoots a bullet that is ~11.43mm.
.223
The typical AR15 fires the same type of bullet as the M16: a .223 caliber (5.56mmx45mm NATO) round. There are AR-15 rifles that have special barrels made for a variety of popular cartridges, even the little .22LR.
5.56x45.223 or 5.56
the m16 uses 5.56 caliber ammo
The AK round. The AK 47 fires a 7.62mm round. The M16/M4 fires a 5.56mm round.
No, you cannot, and attempting to do such would be extremely dangerous.