The manfacture will say not to use a crush washer but as ChattanoogaPhil says some barrels are threaded too long
My Nordic NC22 is threaded for 5/8 and must use a washer. Alignment is perfect


Reguardless if you use a washer or not, you should always remove the bolt and look down the bore.
If it doesn't look right(shadow or whatnot) you should have a gunsmith that's familar with suppressors take a look at it

If the shoulder is square and the bore is concentric it will not make any difference whether or not a washer is used

I have store bought and several Form 1's(homemade) and have had not trouble with the washer/no washer issue on several different firearms

Disclaimer:
My experience only has been with rimfires