ORIGINAL: cayugad
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....
Yes, I am totally positive that I have everything out of the barrel after cleaning the last thing down my barrel is a perfectly clean dry patch and I in inspect the barrel with a light. My gun shop has also done this because he also thought there would be some fowling in the barrel. There isn't. I have not tried the Black Mag 3 yet, but I have tried both ffg Shockey Gold and the Shockey sticks anddid not like the inconsistencies with my groups. Every bullet that I have had down the barrel has been tight at the breech besides the Power Belt and they arenot grouping at all for me with 150 grs of charge, which does not justify my purchase of the Nikon Omega scope. I plan on calling T/C after hunting season just to spend another $50 in shipping back and forth. Hopefully, they can tell me something over the phone. I read on another site about the hole on the one guysbreech pug of his Pro Hunter clogging up. May be that could be inducing a crud ring with all of the powders that I have been using. I use a pick to clean out my plug but I have never used the drill bit that he recommended to clean it out. I have just been soaking it in the new 777breech plug cleaning dish and then picking it until I had no trouble seeing light through it. I don't know may be I am just grasping at straws trying to find something here. Until then I guess the 100 grains of Pyrodex RS loose and 245 grain Power Belt will have to do.