I bought from a friend a DPMS 24 inch varminter, I have had it for years and fired many shots and it was not new when I got it. The accuracy has fallen off as of late. I haven't borescoped it yet so it could be any thing. If it is in fact fire cracked from excessive heat and many rounds, is it possible to set back the barrel? I know this is done on bolt rifles all the time, but I have never heard of this on an AR. It was a very accurate rifle for a long time, and I am not sure if I will get another that shoots as good. If it can be done what would you do with the gas port? Would you just make a shorter gas tube and leave all else alone?