The launcher, essentially an
extension of the rifle, had six graduations for
different ranges (for use in high-angle fire, as
with signal and illumination rounds), and also a
grenade retainer spring. In use, the launcher was
inserted into the stabilizer assembly of the
rifle grenade to the appropriate range
graduation.
A special grenade cartridge, always
hand-loaded, was the propellant for the grenade
mounted on a rifle grenade launcher. The first
widely used grenade launcher for the M1, the M7,
attached to the bayonet lug by a hinged clamp,
and had a stud that fitted into the gas cylinder
valve screw to hold it open and vent the excess
gas from firing this special cartridge. With the
development of the M7A1, which permitted full
semiautomatic fire when mounted, the M1 became
very effective as a grenade launcher. Using the
M3 grenade cartridge, an experienced rifleman
could fire a MarkII fragmentation grenade with
good accuracy almost 200 yards!
The M1 carbine's M8 grenade
launcher used the M6 grenade launching cartridge.
At about 65% the muzzle energy of the M1 rifle,
the carbine could function in the fully
semiautomatic mode with the launcher mounted. The
M8 clamped on the end of the barrel and was held
in place by a wing nut.
There were two basic categories
of rifle grenades: hand
grenades, projected from the launcher by
means of an adapter,
and grenades specially designed as rifle
grenades. Chemical and pyrothechnic signal flares
might be of either
type, with star signal
flares being designed for rifle launch.
Another example of dedicated
rifle grenades was the M9/M9A1 HEAT anti-tank grenade. The M9
weighed about 1.3 pounds, contained a shaped
charge similar to the bazooka AT rocket, could
penetrate 3 to 4 inches of armor, and had a
maximum effective range of 250 yards (probable
effectiveness about 100 yards).
Gases produced when the
hand-loaded grenade cartridge is fired launch the
grenade. For most of the designed rifle grenades,
however, the thrust was not great enough to lift
them to the desired altitude or propel them with
enough force. Therefore, a propelling charge,
ignited by flame from the fired cartridge, was
assembled in the base of some of the rifle
grenades to provide the additional boost. At the
same time, the flame from the propelling charge
would ignite the black powder of any time train
for a time delay fuze, if needed. Fuzes were
standard in signal and illumination pyrotechnic
rifle grenades.
Because of the heavy recoil
generated by the grenade cartridge, the rifle (or
carbine) was fired by firmly planting the butt on
the ground, turned sideways to avoid damaging the
stock.