what if I, owner of a gun, become mental?
If I "become mental" and cant ride anymore, I can end my misery quickly.
What is the best gun for beer can target practice?!
Few years back I would say Ruger .22 but while those guns are still good, .22s are harder to find. I dont shoot .22 much anymore 
.22 is too small, need at least a .380 [in case of needed for home protection!]
Well, anybody has their own preferences and recommendations, sometimes more than one.

I carry little Ruger LCP more than anything else, small and light .380, but keep GP100 .357 under my pillow. I prefer revolvers to autos.
Bottom line, if you want just one gun, get something you will enjoy shooting because thats the way to shoot it well. Would not hurt to go to the range and try shooting different handguns before you spend the money.
My $0.02 only, of course.
