Colt "30 Salvo Squeeze Bore"
30 SSB "Triplex"Military Experimental
The Colt 30 Salvo Squeeze Bore or 30 SSB is a
very rare experimental cartridge with three projectiles
within the case neck, which was developed by Colt in the
late 1960's to early 70s and based on the original invention
of  Russ Robinson in 1903.
Russ had observed that squeezing multiple-
stacked-projectile rounds would cause them to reliably
separate due to air trapped between them. In this
application, special tapered muzzles were developed for
the M60 Machine Gun.
With each shot, the three (55 grain .22 caliber) projectiles
would emerge from the muzzle of the firearm and spread
out to increase the probability of hitting the target.
The rounds were fabricated at the Colt Research Center
using commercial Remington 30-06 cases, increasing the
length of the neck to hold the three nested projectiles
(similar to photo shown).
As you can see from the markings on the box, each one
was test chambered for fit and reliability in a specially
chambered M-1 Garand, which puts a small dimple on the
primer by inertia when the firing pin comes forward.
The experiment was dropped after a few years as the U.S.
Armed Forces lost interest in the project.
These was never in mass production of this cartridge and
these are truly a rare find, and we only have a few