OK, time to enhance the pump action 20mm cal slingshot crossbow.
I exchanged the part that "pushes" the BB forward, from paracord to steel.
The paracord sometimes slid between barrel and ball, and of course it never lasted long due to the unavoidable chafing.
Also, the bands came into contact with the slide, causing early band breakage.
Now, the bands will never touch anything during "flight". Two wooden blocks catch the metal rod, which is padded by Thera Tube Silver.
This seem to last looong, I did many shots tonite.
If this works, I may be close to publish blueprints.