If you had to rely on one bullet...
I carry my 38 Special derringer most of the time.
It's as reliable as a brick and it's (most importantly) convenient for me.
I currently carry Buffalo Bore wadcutters in it, amazing penetration (but also amazing recoil).
I've been thinking of changing the load since my wetpack test shows that the wadcutters penetrate almost too well out of a 1 6/8 barrel w/ no cylinder gap.
So the question sits: if you had to rely on one shot from a belly gun, what would it be?
Don't tell me I need to get a revolver (because i do), I don't have the time right now.