[Hugh]

GT,
I have run into this problem a few times, sometimes it was so close that a little extra "elbow grease" tightened it on up, but left a gouge mark on the end of the bbl. On the others, it was necessary to file a little metal off the end of the bbl to give clearance. Be sure to check headspace after removing any metal from the end of the bbl. But you are doing this anyway after installing a bbl aren't you?