Flash hider installation question
I recently had a "post ban" AR15 made pre ban by having the muzzle brake removed and having an A2 flash hider installed. I noticed that there was not a washer installed on the barrel before the flash hider. I took the rifle back to where I had the work done and they said that the washer is just used as a "timing" spacer to get the flash hider to line up correctly when it is installed. I was told that factory thread jobs on AR15 barrels are not matched to flash hider attachments and therefore the spacer washer has to be used. Any and every AR15 that I have seen has a washer on the barrel in front of the A2 flash hider.
My question is: Do I need that washer on the barrel with the A2 flash hider or is the above correct?? I thought the washer was a "lock" washer to prevent the FH from getting loose.
Any and all thoughts would be appreciated.
Thanks.