[b_t_s]

The old prison favorite of a lock in a a sock can very easily be fatal & probably weights 1/4 to 1/2 of a pound. I once reforged a ball peen hammer into a 1 handed warhammer. It was either a 12 or 16 ounce head, so quite light, really too light to get full power. It was shocking how much adding 6 inches to the handle increased the power. The spike end would easily do 1.5 to 2 inches through plate steel(maybe 3/16 or 1/8 inch) & even the sharp(90 degree) corners of the hammer head would pierce that plate if the strike wasn't flush and peel it back can opener style a half inch. It really takes very little mass to break bone provided you can get good speed, a relatively hard small impact point, and no armor/padding in the way. Skulls, hands, forearms, and shins are very vulnerable.