Did some online digging and while I could find no authoritative information I did find some discussions in other forums which agreed with you.  What I considered a barrel nut is actually a broadened flange-like area on the muzzle end of the barrel.  That flange traps the shroud in place.  It seems to me that there still would be tension generated in the barrel but I don't know if that would give any accuracy gain.

Stu