I would submit that the S&W 649 Bodyguard Airweight is the classic "belly gun". The integral "shrouded" hammer facilitates firing from inside a coat pocket with much, much less chance of a malfunction caused by pocket material interjecting itself between the hammer and frame; I know, a pretty specious concept, but "belly gun" does conjure up some pretty desperate images/situations, doesn't it? It is not completely shrouded though, so one could, with great care (and time?), thumb-cock it for a deliberate, single-action shot; with a two-inch barreled snubnose, also a pretty desperate tactic.
I own two, one in .38 special, and a new 649-3, in .357 magnum (not rated for +P). Having said all that, they do not tend to be the gun(s) I'm never without. That distinction belongs to my Beretta Bobcat in .22 LR. It size and weight just lends itself to inconspicious assimilation in a variety of clothing, circumstances, etc. However, I would never call it a "belly gun"; I would never aim at the abdomen with a weapon of this nature. My ammo (Winchester Super X) has been selected for reliability alone, and I exlusively practice rapid, aimed head-shots at a range of 5 yards.
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