Reminds me of the “bang stick” that Jacques Cousteau and his divers used to use against sharks. Same principal. Had a shotgun shell spring loaded at the end of a long stick. Sharks came sniffing around wanting to munch of the divers and they would jam the stick into the side of the shark. It would go “thump” and the shell would spray pellets into the shark, which would then keel over and nose down, trailing blood like a wounded WWI fighter plane trailing smoke and spiraling in.

Wouldn’t be too hard to adapt the “bang stick” technology to the end of an arrow. Spring loaded tube screwed together with a cartridge in the end. Don’t even need a barrel, since the whole point of a barrel is to stabilize the bullet on the way to the target. I don’t think it would make much noise going off, being as it would be pressed up against an animal’s hide when it did… more of a low “thump”, since the hide and meat would muffle the report.

Of course, if I did make one – even just “proof of concept” that I would never use – the ATF goons would probably come for me… making some verboten ****, or whatever their Rule of the Day currently is…

The wicked flee when none pursueth..." - Proverbs 28:1