The Viven-Bessiere grenade was origanally a french design, but adapted to American Rifles in preperation for WWI. There were over 685,200 VB grenaded shipped over seas during the war. You could launch 2 vb grenades at once, and live grenades are typically painted gray with a unpainted brass fuze. The grenade was loaded into the launcher, bottom end first. When the rifle was fired, the bullet, followed by propellant gases travelled up the barrel and entered the central tube. The gases following the bullet could then launch the grenade. The bullet continued up the central tube hitting the striker and driving it into the primer. The primer ignites, blowing out the wax plugs to provide vents, and igniting the delay train.