WGC Custom Guns:
CQBR:
mk18 mod0:
As far as I can tell, the only real difference are the receivers...
Also, several years ago, I did a CQBR replica. At the time, no airsoft Crane stocks were available, so most of my replicas weren't too accurate. However, at the time, there were some CQBR samples that used the standard M4 stock. Back then, the designation referred more to the upper, handguard/barrel setup and not so much the lower/rear of the gun. It was simply referred to as the "CQB-R upper". I don't even remember who I spoke to, but I contacted via email some guys who had access to and/or seen the real thing and said the lowers varied at the time, anywhere from Knight's to Colt lowers and the stocks were generally anything the operator preferred. I also recall coming across a national catalogue database that listed no actual "CQB-R" rifle - only a "CQB-R Upper" which could be attached to any lower/rear that the SEAL operator preferred.
Anyways, check out the gallery as I have different setups shown with pictures of actual operators with the first generation NSW DEVGRU CQB-R:
http://www.pbase.com/illusive_airsoft/devgru