I don't know about smokeless ammo or how that comment is valid on a trad arms board. But I use t-7's a bunch.
The stuff likes' a water based lube. the "crud ring" you speak of is common. Don't worry about accuracy for the first shot or three, any kind of petroleum or wax type product will result in "build-up'.
t-7 is a hot, sporting grade powder,(tried Swiss?) and need's to be cared for as such. if your use too olde school" then drop your charge a bit,, an "spit swab' tween shot's,
The fouling from t-7 is so far different than "Goex", it does require different school. Use more water based stuff and less wax,,,,,,,,,swab more.