Used to sell a lot of these S&W Mighty Midget tear gas and smoke grenades decades ago in the cop shops, during the riots.
It's too bad a military grenade this small and light can't have the full blast and shrapnel effect.
They could be manually ignited by banging the plunger hard enough to sever the copper safety wire and throwing them, like the WW2 Japanese grenades that they pulled the safety pin on and banged against their helmets to fire the primer.
They were almost always fired from shotguns and bull barrel revolvers using launching cartridges.
The one is this launcher is backwards - the firing plunger went in first so that the muzzle blast would jam it forward, sever the copper safety wire, and ignite the time fuse. That heavy duty cotter pin "safety wire" would result in a 100% guaranteed dud.
There were 12 ga. launching cartridges for the light Mighty Midgets or the much heavier canister grenades fired from a clamp on cup launcher. They were not the same cartridge.