A buddy brought by some scrap from a local manufactory. They do special metal fabrication and he thought I might be able to use this, out of their scrap pile.
That's a 10-inch disc of 316 stainless. He says that it's very hard, tough, and they have to use special tools to work it. Normal bits won't cut it, they had to drill those holes on the plasma table. I'm going to hang it on the 100 yard line and see how it holds up.