The observation is this - when the cartridges are expelled, they seem to have a powder residue in a semi-circle shape (half-oval) on one part of the case mouth out to the middle of the case. All function is normal - rounds are accurate, cycle the weapon, the slide locks back when I'm keeping my dumb thumbs off the release, primers look great, and fouling appears to be normal (copper jacketed or plated lead rounds on AA#5 and Blazer brass). If I had to guess, I'd say I was underloading the cartridges and the mouth was not expanding before the burning gases were rushing around to the outside of the case. I don't have a chrono so I don't know how hot my loads are, but I am meeting published specs. Ideas?