Oh, yes, the 40 mm grenade.......The blooper gun.
This one uses the hi/low system. Main propellant charge fires, the gas fills the casing(easing the pressure) than the projectile goes flying.
The actual grenade is quite complex, and gave rise to a new branch of surgical procedure. Icky biz, that. Live bomb in the body, neither doctor nor patient best pleased.
This system was also used in the Dynamite Gun, an infernal contraption only used in anger once-to good effect, too.
It launched a dynamite charge, the hi/low eased the shock of the firing, which was good, otherwise, the shock would have set off the dynamite, much to the chagrin of the gun crew.
In the Phillipines, the Moro rebeldes took shelter in mud forts, immune to rifle and machine gun fire,. Black Jack Pershing had a few, and used one to blow a Datu's fort to Hell and gone. Once was enough, the Moros booked,
Picric acid shells arrived soon after, and the dynamite gun was history. But so were the Moro forts.
Tear gas guns, flare launchers and other things work this way-why not a vampire stake shooter?