This steel backstop is made very easily. First, you get a local fabricator to cut a piece of 3/8″ thick steel plate 12″ by 18″. Drill holes in the 4 corners for screws.
Now you get two 12″ pieces of 2×4 lumber and cut a 45 degree angle on one end. Since 2×4 is actually only 3 1/2″ wide, you allow for that, and cut two more pieces of 2×4 only 8 1/2″ long and then cut a 45 degree angle on the end. This will now make a right angle that will support the steel plate at 45 degrees from the ground.
Screw the wood to the steel plate and paint entire unit a nice gun gray with high quality outdoor paint.
You have an opening at the “mouth” of the trap that is 12″ tall and 12″ wide, save for the edges of the 2×4 wood, which makes a very handy support upon which to staple a target. Naturally you want to avoid shooting into the wood, so aim carefully.
When you shoot into the steel plate, the bullets angle down into the ground at the back end of the trap. I have shot all kinds of loads into it with no damage. But I have NOT used .44 magnum on it. It’s possible to get a small dent from these high powered, jacketed bullets. If so, you could always step up to 1/2″ steel plate, but I think that would be overkill. There is a small amount of lead splatter to the sides of the trap, and you may want to attach some plywood triangles to the sides of the wood. It would make it look more attractive, too.