I had built a 11.5" pistol and messed with it for a while. the muzzle blast with an A2 was obnoxious. Bought one of these, just to try the concept, before committing to the device from a better company at a greater price.
https://www.joeboboutfitters.com/Kaw...ear223-blk.htm
It definitely mitigated the blast, and noise away from the shooter. How well, and how long that cheap one would last I cannot say, as I sold it shortly after the first round of the Gub'mint rule changes on braces and pistols. For what it was, it made shooting 5.56 from a short barrel agreeable.