I would also ask, the rifle was cleaned and free of all oil before shooting? Were you swabbing between shots? Were the XTP's the only projectile you tried? And do you have any powder other then APP?

I would also get some Pyrodex RS. Also move up to 25 yards to work your groups, there are too many things that can change at 100 yards. Be sure and do a good job of swabbing between shots. I am sure the rifle will come around and tune in real fast.