Asbestos underware on....
I personally do not shoot steel-cased ammunition in my ARs.
I am not saying that you should not.
I hold a personal theory that shooting steel-cased ammuntion is fine is that is all that you shoot in it. However, I believe that the reports of AR's choking on steel-cased ammunition have to do with mixing-and-matching steel and brass cased ammunition.
You see...
Steel jackets don't expand as well as brass cases. This MAY allow for more build-up in the chamber of the AR. Keep shooting the same ammunition that does not expand as much and you will probably be fine. However, if you get build-up in the chamber and then shoot a brass-cased cartridge, you may get the case stuck in a "tight" chamber.
It is the only rationale explanation that I can come up with on why some ARs work well on steel-cased ammunition and some choke.
Well... that is the only explaination that I can come up with besides the possibility that some may have tighter chambers to begin with.
Either way, mine shoot fine with brass and I don't want to rock that boat.
-- John