The AAC SR7 is their latest 7.62 suppressor. It's the same size & weight as the SDN-6. It uses the new 90 tooth Racket Taper Mount, which suppossedly eliminates any wobble that some people were experiencing with the 51T mount. A designer at AAC said it is a SDN-6 with updated exterior styling & a new mount. A local AAC dealer said he probably wouldn't have the SR7 until June or July, so you're looking at Nov./Dec. for getting your Form 4 back from the BATFE. MY upper came with the 51T mount. The price on the SDN-6 should be dropping with the intro. of the SR7, I'll probably wait a couple of months, save some $, and make a decision then.