I cut up a semi-truck mudflap and hang my plates with that. I use the rebar and bracket system for portability, compactness, and cheap replacement parts. The mudflaps can take many hits before breaking. Notice the bullet holes in the rubber...
deputy30,
AR500 steel, or mild steel? All steel is not made equal when it comes to sound resonation after a hit. AR500 resonates better than most mild steel. Thicker steel also doesn't resonate as well as thinner (3/8", or at most 1/2") steel.