I've got an acquaintance who works in a metal shop and he saw me fooling about with steel targets. I've done some favors for him in the past and yesterday he dropped by with a freebie. This guy's shop makes high-end metal products with demanding applications and he had some scrap steel that he thought I might be able to use as a target.
My calipers measure it at 0.276", a tad over a quarter inch. I'll hang it on the hundred yard line, between my A500 targets and my mild steel targets. We'll see how it holds up. If it does well, I might have a supply for hard steel scrap pieces.