your not specifying the standard XTP vs the XTP Mag. The Mag will not expand at all from the colt and on a light skinned animal like deer it will expand very little before exiting from the 454. I've used the 240gr Mag to take elk but it would fly through a deer before it ever thought about opening up. I have shot deer with the 300gr XTP Mag but I've gone to using a 44 mag with standard XTP's and the damage is massive compared to the 454. Your colt I would use the standard 300gr XTP's in with great confidence but the 454 I'd either use the mags for bigger animal, or load down with the standard XTP's. It's an iffy proposition because the Mags were designed for calibers like the 454 but the standard XTP's were not designed to take that kind of velocity. You'll still kill a deer with mags but don't expect a massive exit wound or internal damage, they basicly act like a solid.