Used the search button and couldn’t find an answer, maybe my search-fu sucks, if so please point me in the right direction. Here’s my question, bought an AAC Blackout 51T used from a friend, good condition, good price, but he said it didn’t come with any type of washer and he just had it mounted on his gun without. I checked out the BCM, Rainier and G&R websites and none of them say anything about including a washer. Do I need one? I know for regular brakes and FH’s I should use a crush washer and when I was issued a KAC suppressor and brake last deployment I had to switch to a peel washer, just wondering before I mount this on my gun. BTW, plan is to be able to mount a suppressor once the army decides I’m worthy to live in a gun friendly state.
Yes, you NEED a shim kit and rockset. Go to the AAC website. You can buy the shim kit and rockset there. If you put this on with a crush washer or nothing at all and put a can on it you will have problems. Please use a shim kit and rockset. Happy shooting.
This is not correct. He does not need a shim kit for the AAC Blackout flash hider. Shims are only needed for AAC’s brakes which need to be timed correctly…their flash hiders are not timed like KAC’s or Surefire’s.
Clean the threads, rockset that sucker…and have at it!
Correct. No shim kit, thank you for the correction, I was thinking breakout not blackout. But then again, i do like the breakout better. Happy shooting
HAHA…yeah, I always mix them up while reading, and have to go back and double-check on which one people are talking about.
Doesn’t help that they named like 5 things Blackout. “Oh, look, it’s the AAC Blackout, no, not the flashider, the integral Remingtion, with a Blackout Muzzle Brake attached and another Blackout for your Blackout!” 
Although I did get a kick out of Robert getting the custom Nike’s for SHOT with Blackout written all over them.
To add something of value to this discussion, OP you might look at swapping out your Blackout for a Brakeout. It’s a compromise between both the hider and the brake, but it’s pretty flat shooting.
Big +1. I only run Breakout on both my 5.56 and my 300BLK. It does shoot flat as hell. Buddy has one on his 308 LMT. The Breakout works great on all three calibers.