i had an upper completed with a miculek 6 port compensator installed.  there is a little (1/16 to 1/8in) gap between the nut and the barrell.

I imagine a crush washer goes there.  Do I NEED the crush washer?  Can I shoot the gun a little bit to zero the Arms40 and Eotech and then get a washer?

Any help would be great!

I'll be taking pics soon and listing them under the topic Silver AR in the ar15 disc.forum.

You want something that will keep the compensator from coming loose.  We sell Oly crush washers for $4.00 each.

I believe you're already have the jam nut in place, so it is ok to shoot as is.  A crush or peel washer would fill the void between the barrel and the jam nut, it would look much better.  Don't worry about shooting it without the washer for zeroing purposes at this point.  If you're really concerned about it, then add a drop or two of red locktite on the thread, re-install the brake/jam nut, let it set overnight before shooting.  To remove, just heat it up slightly, the locktite will break bond easily.