This is a cut and paste from a post I made a couple years ago.
The basic setup - bent 1/2" thick rebar with strips cut from a mud flap holding the target. Make a couple holes in the ground and put the target legs in. The stake has been painted at 8, 10 and 12 inches to see how deep the hole is.
The rubber is 2" X 12" long strips cut from a semi-trailer mud flap I picked up at a truck supply store for $8. One mudflap makes a couple dozen straps. Those straps will take a lot of bullet hits and still hold.
This whole thing picks up and fits in the back of the car.
The back with details of the u-bolts. Those are wing nuts but the shock of bullets hitting that target already snapped off one wing on each so I replaced them with regular nuts. The bolts are hardened and will take a lot of abuse.
The little clamp things on the rebar are doohickeys for electric wires. The ubolts tend to slide toward the center of the top frame and cause the target to swing around the vertical axis too much, so these hold the straps apart to prevent that and let it swing straight back and forth.
But I have long since replaced those clamps with duct tape wound around the bar. It works just as well, is a lot cheaper and doesn't come loose.