from The Century Dictionary and Cyclopedia
- n. A device for cutting wads. There are many kinds. The simplest is a circular chisel or gouge struck with a hammer or mallet.
Sorry, no etymologies found.
So, a sniper (one of four) with a wad-cutter round (a flaxen sabot) would take out the window a split second before the kill-shot -- no change in sight-picture, just the window blowing out, clean.
.357 magnum caliber revolver, loaded with magnum ammunition rather than the mild .38 Special midrange "wad-cutter" ammunition the rest of us used because it cut neat, round holes in the target.