I had read a good bit on the Net about these barrels, then stopped by their booth at SHOT; talked to Nathan and Patrick(great guys), that settled it I had to have one.
I bought one of the 18" Gunner barrels to replace a 18" JP that the throat was gone in and have been quite pleased with it. I mounted a L&S MK4 4.5X14 on it. When I first got it I shot groups at 100 with MK262, factory Hornady 75gr BTHP( both shot about an 1") and my handholds with Hornady 75gr BTHP(just under an inch). I then let it completely cool, shot a 5 round group with my handloads(just under an inch), shot a 30 round field course, then another 5 round group. Second group opened up to about 1.25" and had a shift of about .6" to the 6 o'clock.
I don't shoot 3 gun anymore but think that this barrel would do just fine. I love the way the gun handles with the barrel and the price was good. I am looking at there 18" heavy fluted to build another upper for shooting varmints around the farm.
YMMV but I am happy with what I got from them.