Try going to a welding shop and ask for some scrap AR-500 or AR-400.When this is cut with anything outher that water jet, there will be a small area around the edges that will be a bit softer due the the heat annealing the area. The AR-500 is hard and is tough to drill also.This stuff will stand up very well to most anything other than 223's at close range. I was hitting some 1/2" AR the other day with 50 BMG 750 gr A Max's at 500 yards and there's nothing but a bullet spash on the plate.

Here's a pic showinga 6"round 1/2" AR-500 after being hit with 250gr SMK's out of a 338 Lapua at 400 yards, the rectangular plateunderneath itis 1/2" A-36 (mild steel) that the same bullet blew a 3/4" hole though it at the same distance.