Use 100% infill, mine was printed with Prusament PLA and it can tank shots from a Tokyo Marui GBB pistol with no problems (300ish FPS). You can make it thicker (source file included) or stick something on the front to absorb the impact if shooting with something more powerful.
Wear protection and never shoot near pets or other people because BBs can ricochet in wild directions
Shoot the upper target to minimize the risk of damaging the frame
Fix it to something more heavy so it stays in place. No need to use precious filament just for dead weight so I made it pretty light.
If you want it to spin less, glue something to the bottom target. I made it pretty balanced to account for different weights and velocities of projectiles. Adjust it to your own needs!