If you are going to shoot magnums and rifle bullets, you will need 1/2" armor plate, which is heavy, and expensive. Then use that 60 degree angle from vertical to deflect the bullets into the sand. That steep angle gives added " depth " to the plate, and deflects the bullets quickly, without allowing the bullets to damage the steel plate. This is a major problem, considering the high initial cost of such plates, when they are hit repeatedly with bullets. Even lead bullets can bow these plates, and weaken them over time. Its not uncommone to have to take a sledge hammer to the back side of the plate to flatten the plate at the end of a season of shooting.
I do not recommend shooting jacketed bullets at such plates. Its next to impossible to control the direction in which the pieces of copper jacket fly when they explode on steel plates. Only the expensive " snail " traps, such are available from Caswell can handle copper and steel jacketed bullets safely.
As a cheaper alternative, YOu can build a dirt mound as a back stop, with sides to catch any splatters, and then lay a membrane of porous ground cloth, available from arborists, and tree nursuries, on the mound, and then cover the fabric with a couple of feet of sand. The sand catches and stops the bullets. Once a year, you scoopaway the sand, an filter out any lead bullets( most will be in a cluster) and then simply lift the fabric up to collect the bits of lead and jackets that remain. You can replace the fabric with new fabric, or re-use the existing one, depending on its condition. Just put the sifted sand back on top of the fabric, and you are ready to shoot for another year. Sand stops lead bullets rather quickly. Its a good choice for backstop material.
Also, consider building some kind of shell over the backstop to catch any ricochettes that might want to go up in the air. The shell can keep rain off the mound and sand so the sand is not washed down the slope. This is a common technique used in building backstops for rifles. The other is to use baffles at the firing line to keep people from shooting over the backstop. The baffles are built like the roof of a chinese pagoda, so that plates and wooden backers deflect any ADs down into the ground in front of the firing line, rather than allowing them to go down range and over a backstop.