TAB is right MGM targets are wonderful.
Thickness is not as important as the steel type, I like AR500, AR stands for abrasion resistant. Since our range went to using it, with pistol calibers and shotgun slugs, we don't have any more craters in the steel. If you make your own, remember that welding to the target may change the hardness, so if you have to weld, try to do it at the bottom or top of the target, not in the middle. We have some old T10 steel silhouettes that are an inch thick, and they are'nt perforated but pockmarked to beat the band. We have to reface them once a year, or .22's will just go in a crater and come right back at you.