I've only shot Goex in my caplocks and flinters, but I've shot a lot of T7 in my inlines using musket caps, never had a problem with the fouling ring or crud ring as they call it, I think that is an issue associated with the 209 primers which aren't legal here. If Goex was easy to find around here, I would never have tried T7, but since no one sells it here, I started using the T7. One thing nice about it, I can use less of it for the same power, so in that respect, it's good, but at $14-$17 a pound, it's still spendy. I have just enought Goex 3f and 4f to keep my flinter running for a while, tho!
PM me or ask in the Modern or Huntsman forum about breech plug issues with T7.
Tim