Billt... you will put a bunch of residue into the action if you use a chamber insert on an AR with a standard gas tube.. when I used my CMMG A unit for 3 gun practice, I put 1000 rounds of transition practice prior to the 2009 Ft Benning match, by 2010 I had cobbled a spare upper to which I had removed the gas tube, and closed off the gas port with a stainless screw clamp... plenty accurate for what I was using it for... after 2010, I got a 16" dedicated barrel... when I got my registered SBR I got the 10" and short 9mm options also.. regards
my first decision was to build a 10/22 for Steel Challenge... I just was unhappy with the reliability of the platform (mine was not a Ruger receiver)... the short AR works fine for me... I have a 16" backup