I had the same problem with an 03-A3 about 20 years back. Caused by wear in the neck portion of the chamber. I tried all sorts of lubes and ammo. Maybe you will have better luck but it took a new barrel to fix mine.
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I had the same problem with an 03-A3 about 20 years back. Caused by wear in the neck portion of the chamber. I tried all sorts of lubes and ammo. Maybe you will have better luck but it took a new barrel to fix mine.
Sounds like your barrel has insufficient leade. Have a gunsmith check it out. That ring on the case mouth may be caused by the case entering the rifling too far, which will cause elevated pressure by holding the bullet in the case too long. You are either short chambered or your cases are too long.
jt
CMP sold a pile of barreled-receivers that had short chambers. I'll guess you have one. A finish reamer is necessary and a good 'smith can fix it in 15 minutes.