I bought a brand new TC Encore about 7-8 years ago. It's not the pro hunter just the standard model. Stainless steel, laminate wood with thumbhole stock. The last couple years I have noticed it is getting less and less accurate when I sight it in before season. When it was new I could hold a very tight group at 100 yards. I had always shot pellets and this year after reading a lot I decided to try powder. This morning I went out with 777 powder and set up at 100 yards, with a good steady rest. I started out at 110 grains and my first shot was dead center about 3 inches high, about what I wanted. Next shot was 5 inches high and 3 to the left. Next shot 5 hive and 4 inches right.

Just to try I dropped down to 100 grain and first shot was still about 5 inches high and left. After this I adjusted the scope to drop it three inches and my next shot was good, almost X ring. Very next shot was 5 inches high again, so had I not dropped the scope this would have likely been 8 inches high. The scope on the gun is a Traditions brand muzzle loader scope. Are there any go to things I can check on the gun that could cause these issues? Is there a way to see if it is the scope without just going and buying a new one. I hate to spend several hundred dollars for a better scope and still have the same issues. The "hinge pin" (not sure what it is really called) is snug and there is no wobble in the gun and I have to lightly tap it out to remove it. The gun can't have more then a few hundred rounds through it, I shoot it a few times pre season and then shoot a couple deer a year with it. I do swab it with three wet patches and then three dry patches between each shot. I also put a brand new breech plug in this morning.

Any help on where to go next would be great.