Originally Posted by Gene
Trimming brass too far below the barrel chamber length encourages formation of a carbon ring just in front of the case mouth. Eventually this carbon build up will result in severe loss of accuracy if not removed. To keep carbon ring to a minum, trim all cases within about .003" below the SAMMI casre length for your caliber.
There are several methods to remove carbon ring, just google it.
If you use a bronze brush when cleaning your rifle and use powder solvent, this is a non-issue. It's those who choose to clean with patches only or nylon brushes that have odd issues like this. I trim .010" to.015" down from max. and have fired thousands of rounds with everything from 5.56 nato to 405 win with some really nasty bore eaters like the 7rum in the mix. I've never gotten a "carbon ring" in my chamber.
I tried going to shooters choice only for a while(after I ran out of Hoppes) and actually nearly filled the rifling on the 7rum with carbon deposits for the first few inches, but one heck of a scrub down with hoppes #9 and a bronze brush solved that little problem. The shooters choice is reserved for copper fouled bores only now. Funny how the new bottle(shooters choice) says to use powder solvent also, but I don't remember the old one saying that.