Dark Wolf
32 Cal
I have not tried this for black powder, but the same thing might work. I needed to make a simple air pistol pellet trap. Made a square box frame. Fixed a piece of Kevlar cloth that I had to the top leaving the bottom loose with a bit of weight attached to the bottom, so that it could swing.
Same thing might work with a target frame and two or three layers of the cloth hanging and maybe a sandbag on the bottom to reduce the amount of swing. I believe the leaf bags for lawn mowers to be made of Kevlar cloth, or it is available in sheets.
The traps I made for my airguns are filled with rubber mulch. Works very well, and helps with the lead supply for round balls.
DW