Bullseye,
I am currently having what I would term scope problems. I have a relatively new Encore in .270 (purchased in June). Read about it in the, "Help With Encore .270" thread.
I have put probably 6 boxes of shells through it, and I still can't get it to be consistent.
The really odd thing is that as I dial up the power on the scope, the gun shoot higher. The point of impact actually changes (which is totally weird).
In my case, I am going to call Thompson (or email them) and reference the thread. That way they can get a good idea of what is going on and what others think, as well.
I will tell you to use a bench rest and try various ammo. This gun if tricky. Some ammo shoots well and some just doesn't pattern.
And I'd try swapping out the scopes, but the only other scope that will work on this is sitting on my deer rifle and all ready for the season.
Good Luck!