RE: T/C Shockwaves and Pyrodex
Personally, I'd steer clear of the magnum powder charge. I shoot the 300gr SST/Shockwaves over 80gr of loose 777 and get one hole accuracy and 1500fps at the muzzle. Pushing the 250 with 150gr of Pyro is more than likely not going to give you great accuracy. Acceptable maybe - but not great.
And I would suggest trying the 300gr version as well - they will often shoot better than the lighter bullets.
For plastic fouling, you need to use a bore brush to do some good scrubbing after you're done shooting for the day. CVA makes a solvent called Advanced Shooters Sabot solvent thet you can patch thru to help disolve any plastic. OR you can use a couple of patches with hardware store Acetone on them - that stuff will sure knock out soft plastic. This is above & beyond your normal cleaning to removed the powder fouling.