dude I think making guns isn't hard

(rudimentary guns)

just take a metal pipe
some metal thing of the same diameter
powder which you can get from buying fireworks on other side
and do some magic step where powder is inside the pipe with nowhere to expand being blocked on one side by solded metal and on other by <some metal thing of the same diameter>, and get the powder to combust somehow, while aiming the open end of the pipe at a safe target

BLAM, INSTANT GUN

dude, slam fire 12 gauge shotgun, look it up