I have one on my Sendero .300 win mag. I feels like a .308. This is a great brake. Mine was installed by GAP. You have to look hard to see the line where it meets the barrel.
Here are some other of his later designs http://www.tttmissionfirst.com/rifle_muzzlebrakes.html . Rick owns the patents now but there are some nice advantages to some of these like closed bottoms for shooting prone .
+1 on Vias. I put one on my Rem 700 Sendero .300RUM and it's a pleasure to shoot now. It comes off easily, and my smith made a muzzle cap to fit over the threads (as some outfitters/guides will not allow a break).
I also don't think they are as loud as some other kinds of breaks. I do get a hell of a lot of dust if I shoot prone.
They are great brakes for hunting rifles for sure, but if your going to put it on a prone gun, they throw some serious debret everywhere. Especiallly if your shooting a match and there is someone next to you, they get a bit upset. But they do work well.