I think personally, I would be changing powders. Although to be honest, that does not seem right. You own one of the best rifles made by Thompson Center. If Thompson Center says to use Pyrodex I would give that a try. Yet is does not seem right that you can not use the powder you like. You might also want to look into some of the Black Mag3 or even American Pioneer Powder and see if that does not cure the problem. I am guessing that for some reason, climate, elevation,who knows, that the rifle does not like Triple Se7en Powder. For that reason, I would start changing one thing at a time and see if it makes a difference or not. When the rifle starts to behave then go from there...