What about this idea, which is what I have inside my shed, which I shoot at from 40 yards away in my house! I find that shot on shot pellets soon penetrate 4 carpet tiles, so I did the following.
I have 6 off 600x600 carpet tiles. I have printed targets on standard printer paper. You could fit 6 paper targets on the carpet face, but if instead of just sticking multiple targets to the carpet face, you arrange a system where the paper target Is held in a stationary holding frame and the carpet tiles are made to move horizontally 400 mm and vertically 300 mm, then wherever the carpet tile ho