I had posted my GAU-5/A/A (like the one I had in the USAF Reserves in the late 70s) clone on the 1990s "US Armory" prototype receiver from when I had a manufacturer license. Because of the flash hider, though, I had to use a Juggernaught tactical mag lock set up and could not have a detachable magazine or a magazine of more than 10 rounds, since I live in Commiefornia.
So I decided to change from the XM style barrel to a chrome linned Palmetto (H&R) 14.7" barrel. I pinned a A2 style muzzle brake on it for 16.1", blocked the stock, and put a compliant Sparrow dynamics grip on it. That way I can use a standard magazine release and legally possessed 30 rounders (from my LE career and Freedom Week). The last year in the reserves I had a GAU-5/P with the 14.5" barrel and 1/12 twist. The 14.7" pencil barrel I got, though is 1/7 so I can shoot my MK262 MOD1 77 grainers.
I bore sighted it at the gun shop I work at, so it would be close. Last week, I took it out into the woods in Oregon on a recent trip to my daughters, and blasted away. Off hand, I was nailing pop cans and pine cones from 25 to 50 yards with almost monotonous regularity! It only weighs 5 lbs, 7 ozs empty. Nice and light weight. The 14.7" barrel looks MUCH better than a 16: with flash hider.