[dbarn]

Well, to follow up on this thread, I tried to use the crush washer and it would not fit flush to the barrel.

With AAC's washer the CTR has some kind of shoulder between the threads and barrel that would not allow this washer to fit flush when tightened. In other words there is a small gap. Yes, the washer was installed correctly with the cup portion facing forward.

Contacted AAC and spoke with a tech. He said to forget the washer. Clean with alcohol and use a few drops of Red Loctite, then just install the AAC FH using a wrench but just snug. Heat will allow any possible future removal. The fit is perfect with no gap.