I have a couple of 1/2 inch plates to set up (for pistol)and am going to mount them with two pieces of 1/4 x 2" flat bar, welded to the back at +- 30 degrees. The flat bars will pivot on a pin at the top and there will be a stop so it can only swing back but not forward. Should deflect rounds down and allow the plate to move back with the impact but not pivot forward enough to deflect bullets back at the firing line. Just remember to allow for the angle when cutting the plates, a circle will need to be cut as an oval and square will need to be cut as a rectangle.
There was a one inch thick mild steel plate at 100 yds (hung plumb) at the range and although rifle bullets had not punched through it, the surface looked like the moon. Some craters were more than 1/2 inch deep.
