A cardboard box full of rubber mulch can be made in minutes. It's cheap and quiet.
Ted, see the piece that the "bulldog" target clip clips onto? Find a metal shop to duplicate that for you. Because inadvertently you will either shoot that or the clip. Like I said before, if you have two of the them & slide each one to outside upper corners, you will prevent a lot of that problem. And get yourself some magnets too.
This is a picture of my 15 yard cellar range. I have various traps and they all work very well. The Do-All I have was meant for 22 rimfire as has seen thousands of 22LR put into it. All the traps I have, from the rag filled cardboard box, to the Champion ballistic curtain, and up to the Do ALL bullet trap, capture and retain pellets from all the guns I have listed.