This are great for mini firearms, they are simple and easy to make.
First you need
fuse (you can make or buy your own)
Acquire some .22 bullet shells, do no use live rounds.
Drill a hole next to the end of the bullet.
Place a fuse in the hole and sit it on its end.
For your lead shot use solder that has beed melted so its in a ball shape.
Now pour the powder into the shells and push it down with something, then drop a few lead shot in, then you take a bit of cotton roll it into a ball and push it into the top sealing the bullet off.
Thats it have fun fireing.