Re: 762 SD on a SBR
This will work fine. I have a 11.5 and 12.5 ....with m4-2000's. My shooting partner runs his m4-1000 ( earlier gen- I think its m4-1000?) with 18T mount with 10,000 rounds through it, his is 11.5 inch SBR. No issue.
Your 7.62 will work fine. I suggest the double chamber AAC brake to use as pseudo baffles. For that SBR, I would get the shorter , newer 7.62 SD-n6. Or m4-2000.