Flash hider over-torquing?

I've seen several flash hiders that, when used with the A2 style crush washer, required more than a full rotation to index correctly at 12 o'clock (they originally indexed, finger tight, just shy of 12 o'clock). This is putting way more than the specified 15-20 lbs of torque that Colt recommends and even more than the 25-30 lbs that the KAC M4QD recommends.

I just installed an Armalite AR-10 flash hider with an Armalite crush washer. It only required a 90 degree turn but at least 90 lbs of torque was required to move that 90 degrees.

What's the story with over torquing flash hiders? I'm told it's a quick way to destroy a barrel/accuracy?

The problem you're having is that the torque figures you're looking at are meant to be used with the peel washers where the torque needs to be high enough to hold it even when it heats up.

With a crush washer you should just get it snug against the washer and then go to alignment. You don't have to worry about torquing it down because it is a type of lock washer and it will hold the hider in place.

If you have one that needs more than about a quarter turn to get aligned then the best thing to do is to tighten a little then loosen it, tighten it a little and then loosen it. This will crush the washer down without putting so much tension on teh washer and on the threads.

This is why I prefer peel washer whenever possible. My 3 gun rifle has probably no more than 8-10lbs of torque on the muzzle brake to hold it on with a peel washer (just barely more than hand tight, it hasn't shot loose yet in over 5K rounds). Excessive torque at the muzzle can effect accuracy as the barrel temperatures change.

Thanks for the advice on what I will call "pre-crushing" on the crush washer when faced with say, more than a few degrees to reach top dead center.
I am often asked about crush washers with our (KAC) QD Compensators, but don't have an answer because we have never tested them against our 7-Piece Shim Set/Rocksett combo that is packaged with our sound suppressors.
I like the "pre-crushing" concept, except I think I will will do this on a "slave barrel/muzzle" so as not to place any of this potential undo stress on the barrel I am actually going to install the crush washer on.

Crush washers are a poor, poor replacement for the peel washers as far as I'm concerned. And, in my mind, over-torquing a FH is a big issue. I like to put them on just beyond hand-tight in fact-- and have not had a problem with them coming off. I do Loctite them on customer's guns but not on my own, just to see what happens and they just never come loose.

I have yet to see a crush washer that crushes and allows the proper adjustment without over torquing. I have to wonder if there is another crush washer that was the original idea but was less available so companies started buying the current ones....they flat don't work unless you get lucky. I just use them as spacers and surface grind their thickness to whatever is the right dimension for the barrel being worked on, to get the torque and alignement I'm looking for, add a couple drops of LocTite and go.