.45 calibers can be tempermental according to some posters. I personally have no experience with that caliber. Although if the rifle does not shoot the XTP well, then you have to try some other things. First thing I would do is get some loose Triple Se7en 2f and load 80 grains. See if the rifle behaves better with a smaller powder charge.

Alsoyou could try some other projectiles like Shockwaves, Powerbelts, Saber Tooth Conicals, even maxiball. There is just a trial and error with a lot of these rifles. I also agree with you, I would not be happy with a group that size.