taurus 45

[Contenderizer]

Don is correct, the caliber should be clearly marked on the gun.

In any case, you should not be experiencing blow-back. Factory 45 LC ammo is often loaded "light" for Cowboy Action Shooting and its possible your brass is not expanding enough to properly seal the chamber. On the other hand, you may have a headspace problem or the gun may be firing when not in full battery. Any of these issues could cause damage to the gun or injury to the shooter. I suggest you talk to Taurus before experimenting further.