That grip works and is pretty traditional. Another good option is the straight thumb grip, which takes awhile to get used to, but you'll find yourself getting onto target faster with it. Looks like this..roughly:
I would be *very* careful with frangible ammo. Yeah, you won't get much for penetration through a wall..but you also won't get much for penetration into a human. You need to get a round deep to hit the vital organs and a bullet exploding and not penetrating isn't going to stop someone. A lot of the ballistics tests on the pistol frangible rounds ..are less than encouraging.
Truth of the matter is...if you can effectively penetrate a human deep enough to get a vital wound hit..you can probably penetrate a wall. Sucks--but thats what the ballistics say.
Some good info via these guys:
http://www.theboxotruth.com/docs/bot2.htm
Also some good stuff showing the frangible rounds hitting basaltic gel out there as well...and still..less than encouraging.
00 works pretty good. It gives you the penetration you need. Those that use bird shot will be disappointed. Just remember this--just because you use a shotgun doesn't mean you don't have to aim (people tend to think this). At 12 feet you're only going to have like a 2" spread. Of course, anyone that has handled a shotgun a little should be able to rapidly pointshoot 10 feet no problem.