What caliber XTPs did you buy? Are they .44 (.429") or .45 (.451")? I believe I have Harvester smooth and crush rib in each and I could send you a couple to try for fit. IMO the XTP is all the bullet you need for deer. I've used them with good success in the 300 grain version both .44 and .45. I also use the 295 gr Barnes T-EZ bullet
As for the powder choice its up to you whether you want to use Blackhorn 209. If you do I would recommend the BH209 breech plug as previously stated. But there is nothing wrong with using Pyrodex RS, Just a bit dirtier. Lately I've been experimenting with Alliant Black MZ powder and getting good results out of my Accura V2. And the one thing I've found is that you really have to compress it for good accuracy.