Regarding Reloder7 and IMR 4198 in .45 Colt: Weirdly, whilst there's not a nickle's worth of difference in the .44 mag., the two powders don't act the same in the roomier .45 case. Re7 seems too slow. IMR4198 works much better when either powder is loaded to the base of the bullet. Most particularly with 200gr H&G SWCs.

Aside from the powder position sensitivity, which is even more pronounced in .45 Colt, I'm not sure the gains are as worthwhile using 4198. Leading isn't as bad, even using 8.0 gr WW231, as with the .44s.
Accuracy tests ongoing.