nymike,

Is this the rifle that you struggled to get the barrel nut loose on, finally machined it off? You thought it had been pinned, did you determine that to be true? The upper would have some hole drilled in it, probably in the threads. Just curious. Wondering if S&W went that extra step to insure that model was compliant and could't be readily changed. That might explain the 223 barrel. Also, what FF did you install?