simple and smooth, or a great big PITA. Worst I've ever done was forming .30 Nagant from .223; easiest is a tie between .308 to .338 Federal, and .223 to .300 Blackout.
I'll also throw in, wish I'd known of the lanolin & alcohol method a long time ago.
Speaking of, I'd love to take the .338 out for a spin, but the shoulder's not quite ready for that, I think. Though the most difficult area now is the area around the end of the collarbone where they cleaned it up, not the area of the tear, which seems to have healed up nicely.
Speaking of, still doing the PT stuff but working in something of regular workout stuff, too. Carefully. Regular pushups, for instance, are right out; only leaning-to-the-wall type still. I really need to find a gym that isn't too far away and doesn't want to rape you on fees to join, I think having weights to use would help a lot.