That plastic has amazing force until it slows down. I dented a friend's chrono when the wood block I had taped across the front slipped and the sabot caught the top of the frame.
Plexiglass or plywood will work fine as a blocker.
Another tip, forget the metal guide rods on the screen. You can guarantee the bullet will go through them but where will the sabot go? Hit one of them and bye bye sensor block.
My suggestion is to substitute uncooked spaghetti strands. You can't put the sky screens on them, but if you don't neeed the screens they work great for guiding your shot without risking a hit.
