I have always used adco barrels and thought I would give Spikes a try. I normally run my 9mm ar platforms suppressed but sometimes do not and I utilize a thread protector, etc.. when doing so.

On all my adco barrels, I get a flush mount with my fixed barrel mount for the octane, I get a flush mount with any attachement.

On this barrel I am not. I dont seem to get a snug stopping point?

I cant imagine it needing a crush washer or spacer, its only 5.5 inches. Thoughts? Should I return or is this normal

Crappy threading with no thread relief. At best use shims made for suppressors to make it work, do not use a crush or peel washer.  I'd send it back if I was going to use it with a suppressor.

Return it and get a ADCO or TROS barrel.  There's nothing worse than having to "make" something work after you buy it.

bingo