Can you put bb bullets in air rifle?

Only if the gun is designed for BB's. Some air rifles are designed to shoot either. Usually they are the multy pump design like the Crosman 760 or the Daisy 880, but air rifles will say right on the barrel that they are designed for .177 cal pellets or .22 caliber pellets and these rifles or guns should not use BB's. BB's will damage the rifling in the barrel.