Monty,
I'm no expert, or even close to one. In fact I'm as far away from an expert as you can get. So why bother listening you say? Well, the fact that I know so little made me rely on others for their opinions, pretty much like yourself, w/respect to buying a shotgun. Even the much praised 12ga w/00 buck is nothing more than 9 to 12 "hits" with a .32. Like Dave syas, in trained hands a 12 ga is devasting. In my hands, it depends a lot on the shotgun. I have 3 right now, a 20 ga Browning pump, a Rem 870 and a Stoeger 12ga SXS Coach gun. 2 weeks ago, I took the SXS out with a box of S&B 00 buck, just for the fun of it. At 25 yards, the best I could do was 1 pellet on a paper plate. Pretty sad on my part. The bruise on my arm ( note arm-not shoulder) is just about gone now. My conclusion is the Coach Gun is pretty to look at, but in my hands, it's a detriment. OTOH, the 870, while not a pleasure to shoot, is far more manageable. Using the S&B loads, I get an 8" pattern, centered on a paper plate at 25 yards. The downside is that it takes me a considerable amount of time to line everything up. Now contrast this to say my CZ75. I can place roughly 6 shots into the same area, in the same amount of time. Or even my Winchester .45LC Trapper, which can get 3 shots into that area in the same amount of time. Bottom line is, I'm glad I bought all 3, but until I get better with the 870, it is one of the last guns I would use for HD. Since finding a place to shoot the shotgun is harder than finding a place to shoot the others, I don't see much hope for the shotgun(870) at present.(It's simply too much noise and muzzle blast for an indoor range, and it tears up the backstop of the outdoor range, so the owner discourages using them). Once or twice a year isn't going to cut it w/anything. BUT!!! The prices are not likely to go anywhere but up. That being said, if you have the $$,and you have the desire, get one NOW! Worry about practice later. In the meantime, use what you're best with. I would prefer something a bit more potent than a 9mm, but the CZ is proving to be the best I have at present. Best of luck.