Kinda goofy, but i used 2 coat hangers and 1 of those stringy garter things you hook onto a facemask (facemask holders i assume)

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It doesnt have the trigger and catch though, so you have to pull back and release it which can make aim a little wonky (or i just have weak hands lol)

I got this idea from the sheer fact alone this was possible because of the plunger and every thing else was put together to be one by welding or screws, excluding trigger and catch.