I know this sounds feddy, but bonus if they’re improvised, cos that shits awesome.

One of my favourites is the PRIG - an IRA made grenade launcher that used a packet of biscuits to offset and quieten the backblast.

I also made a crossbow that fired nuts and bolts using wood and resistance bands. Not a weapon of war and would never be lethal, but also probably not very legal where I’m from. I just used it to plink cans in the back garden when I was bored. Was actually quite a scarily powerful and accurate device for how crude it was.