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...

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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.