Thanks Kevin, I have been using IMR 3031.
Okay, this could be a problem. 3031 is a great powder and certainly appropriate for the .223 and being an extruded IMR powder, it's generally an efficient burning powder and ought to burn clean. The only potential issue (and I say potential issue, because I've never used 3031 in an AR), is heat. Most IMR powders burn rather hot, and where heat plays a role in the AR is inside the bolt carrier. The expansion chamber behind the bolt is where heat can collect and transfer to the ousides of the bolt carrier. If you heat up that bolt carrier much, it degrades your lubricant significantly.
Now all this depends on how hard you're working your rifle. If you're really spraying down the whole zip code and having a lot of fun, this could be an issue. For "normal" shooting, I doubt this is your problem.
