Well it sounds like the Triple Se7en is your problem. Have you considered a different powder? Even Pyrodex with three pellets might not produce the hard crud ring and allow you a second and even third shot without swabbing the barrel. Of course a lot of people do not rush the second shot and they swab, even out in the field.

If clean burning is what you're after then you might want to look at some Pinnacle E-Z load sticks, American Pioneer Sticks, or Black Mag 3 powder. These will be clean burning and should give you some excellent performance. Black Mag 3 is rumored to be more powerful then 777. I shot a couple pounds of it off and really liked the stuff. Just the cost bothered me.

I can sure understand your frustration when you have that kind of investment and it does not perform the way you feel it should. Also have you contacted Thompson Center with this problem? They might have some information that will help you. One last question is, are you positive you are cleaning the bore clean of all oils before loading? If you mentioned this fact I missed it in your post and apologize....