HINT: Do you go for penitration or expansion?!
There is a correct answer?
I might opt for pain
Given the weight constraint, how about a can of hair spray and a bic lighter? One push and one flick of my...
Short (and light) bang stick? (12 gauge?)
LCP makes it under your mark, along with a few others in this niche.
If you really only want the one shot, Bond Derringer can get to 19oz at the smallest; and you could only load one of the two barrels! Take off the grips and you might make your 16 oz cut.