My brass gets black on the outside walls. The ACP cases fit reasonably snug in the my home made breech plug which was drilled with a "J" size drill bit (0.277 diameter). Specs for the .25 ACP case are 0.276 neck & 0.277 at the base. I don't think I would want them any tighter. Not a problem really. If I'm shooting heavy loads, like 100 grains or more of loose T-7 and 300 grain bullets, I need to swab out the breech plug with a Q-Tip after every 5 or 6 shots, or the cases will begin to stick a little. With light loads I don't have to do that. Still beats 209's all to hell.