I realize that you are a handloader and have been experimenting with different loads in this Luger, but I have to ask if you have tried factory ammo that frequently has the case shoulder set back farther than many sizing dies will set it back, without "tuning" of the sizing die. The 7.65P round headspaces on the case shoulder and not the case mouth. I am having a hard time understanding how shortening the OAL of the brass is helping you with RTB problems.

Thanks for your input and info - I'll try to get a decent pic of the inside of the chamber as there is a definite "ridge" which appears to be located where it would meet the mouth of the casing and the "trimmed cases" do seat deeper in the chamber. I have tried this chamber fit procedure using casings from original DWMs to new Starline brass and some older Winchester rounds I scored . I really appreciate having so many knowledgeable firearm enthusiasts making suggestions as on my pension I can't afford to send it off to a reputable gunsmith.
Like Arnold says - "I'll be back!"
Thanks again Bruce