I have three main handguns that are "in the rotation" for both HD and CCW and are thus kept loaded in a separate safe. All three of these guns are S&W revolvers so I do tend to stick with basically the same platform (they are different models and frame sizes though). I do not, however, limit myself to one caliber as the three guns in question are chambered for .38 Special, .357 Magnum, and .44 Magnum. I don't really think of commonality of ammunition or reloading as much of an issue for HD because I figure that between three loaded revolvers, a loaded shotgun, a loaded semi-auto rifle, and a fixed-blade knife that if I can't solve the problem a reload isn't going to do me much good.
Smith, and Wesson, and Me. -H. Callahan
Well waddaya know, one buwwet weft! -E. Fudd
All bad precedents begin as justifiable measures. -J. Caesar