We recently rebuilt our range using steel baffles. AR500 steel 1/2" thick will stop a .470 NE 500 gr. solid at 10 ft. We had it tested at White Laboratories. Setting the steel at an angle with a sand pit under it should work.
I know we are talking about rifle bullets� but our Naval Reserve Center had an in door pistol range set up just like that in the 70s. We shot .45s a lot.
They said it was old Cruiser Armor whatever kind of steel that was.
