Looks like LWRC. It's called the ambi rear sling mount.
I've seen that sling mount before, but I don't remember who made it. I don't think its LWRC though. But there are similar mounts: TangoDown PR4, TROY OEM, TROY pro grade, DD EZ Car QD, Midwest Industries HD QD, etc etc.
Looks like the one built in to a PWS buffer tube to me..
Originally Posted By TREETOP:
Looks like the one built in to a PWS buffer tube to me..
I think you're right.. its part of the PWS buffer tube.