For the longest time, I vowed to only buy guns in calibers I could easily find in Walmart. Most of my handguns are in 9mm or 45. A couple revolvers in .357, .38, and .44. Some .22s, and a bunch of ARs, all in .223/5.56. An assortment of 12 gauge shotguns, and a couple rifles in .308.

The only time I have deviated from this philosophy thus far is when I bought a 10mm Glock 20. I have been tempted by the 5.7, but hate that there is only one source of ammo. I have also been tempted by the 50AE, but I have always come up with better uses for the money.