Re: ar400 steel
Buyer beware, unless you get the steel from a reliable source (i.e. Bobcat Steel), you may get something different then what you are expecting. Example, ordered some AR500 steel plates from the local steel supply outfit, when I received the two plates, one was marked AR400 with the standard yellow crayon type marking that steel suppliers usually use.
I called the salesman, and told him what happened, and he wasn't suppried as the guys working out in the yard are min. wage workers, and sometimes don't give a rats-ass to what they grab from stock. I told him it would be a big hassle to return them, and he agreed, and offered a discount on my next order.
Anyway, we hang them out beyond 500-yards just to be safe, and have shot them with 300WM and 50BMG with no issues at the longer ranges.