As seen in my avatar, I used some scrap carbon plate 3/8". It has held up for "me" shooting it. If it was going to be an everyday use or high use, you should use something harder. I made about 6 targets and they have lasted for about 1.5 years now with no visible damage. They have taken about ~4000 rounds apiece, with .22 being the primary, and 9mm and .40 bringing up the rear. When they start to cup, I'll just flip them over for a few years and beat on the other side!!!LOL!