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protection unit

which is why i moved the thread

I've seen the same thing done with a lightweight home-made arrow.
The arrow would rest on the fingers and prevent you from
Smacking your thumb though. That just looks dangerous. Slingshot
Frames aren't expensive.

Sort of silly but I do something similar to shoot flies.   I take a length of elastic cord and knot each end.  The draw is just like a slingshot (or bow) and you hold onto one end while the loose end whacks the fly quite effectively....
You have to learn to "drop" your thumb slightly at release so that the thing doesn't whack you and get deflected.   Same principal as this, I suppose.

We did something like this a school to shoot various small objects across the room, but no one ever used metal.  If a metal pouch/grip hits your thumb it does not feel good... we quickly started using the "hornet style" that keeps your fingers well out of the way.

This reminds me of something that happened to me at school once. Some kid gave me one of those large packing rubber bands (you know the kind that are something like 10 inches long) and I was going to use it to shoot paperclips that had been folded in half to make a "wasp" with a point at the end. Yea...not a good idea I know.

I pulled that thing way back but my middle finger was in the way still and when I let go it buried that paper clip's point a good quarter inch into my middle finger. Guess I learned my lesson. And to add insult to injury the teacher refused to let me go to the nurse. Bad day, good lesson. No one got hurt but me, as it should have been.