Vid-20220418-wa0011mp4 90%

Specific types of paper or cardboard used for making targets.

"Proper paper" in the context of slinging.org likely refers to: VID-20220418-WA0011mp4

Documentation or instructions referenced within the forum attachments, potentially describing the use of a "proper" projectile. Specific types of paper or cardboard used for making targets

If you can tell me is in the video or what material they are using, I can give you more specific information on that technique. Directory /forum/yabbfiles/Attachments - Slinging,org I cannot play the video to confirm, but

Using tightly rolled paper or improvised paper materials for ammo.

Based on searches, the file VID-20220418-WA0011.mp4 appears to be a video attachment in the slinging.org forum . This community often discusses creating, using, and repairing slings.

I cannot play the video to confirm, but I suggest checking the slinging.org forum for the thread matching that attachment name for the exact context, as attachments there often depict experiments with different materials.