Exotic Firing Mechanisms: The Gyrojets

In the world of firing mechanisms, one more development must be mentioned: The Gyrojet or rocket powered bullets. The Gyrojet family of small arms were conceived in the 1960s and a company called MB Associates (or MBA for short) developed a pistol, carbine and rifle using the principle of rocket propulsion.

Unlike conventional pistols, the gyrojet weapons didn't need as thick a barrel or firing mechanisms since the pressure on leaving the barrel was still relatively low. The ammunition consisted of a projectile with four tiny rockets placed at an angle off the center. Upon firing the four rockets, the projectile would spin about its axis and thereby achieve spin stability in the air. In a normal weapon, the bullet is at its fastest velocity just when it leaves the barrel and slows down as it travels in the air. In the case of a gyrojet round, the velocity builds up as it travels in the air. Hence, gyrojets were less lethal in close ranges, but got more lethal as it gained speed until the rockets burned out. In the case of gyrojets, the rockets would burn out approximately 60-70 feet outside the barrel and would reach a velocity of about 1250 feet-per-second at this point, after which the rocket propellant would run out and the bullet would travel under its own momentum. The accuracy was also better than conventional firearms over longer distances, because the trajectory of the round was flatter.

The firing mechanism of the gyrojet weapons was absolutely unique. Like a percussion firing mechanism, the rockets were ignited by a primer which was sensitive to percussion. Unlike a conventional weapon, when the trigger was pulled, a lever would strike the front of the bullet and push it backwards into a fixed firing pin. The force would ignite the primer, which would in turn ignite the four rockets and then the round would move forward.

Unfortunately, the gyrojet family of weapons never took off for a few reasons:

1. They were large caliber rounds and a new Gun law was passed in 1968 which classified Gyrojet bullets as "destructive devices" since they were explosive rounds greater than .50 caliber. This meant people had to pay extra taxes and get a special permit to own a gyrojet based weapon.
2. Didn't offer too much advantage over conventional weapons.
3. Bullets and the weapons cost much more.
4. Loading speed was much slower than conventional weapons

However, the gyrojet weapons were much lighter than their conventional prototypes since they didn't need to be built at strongly (as most of the acceleration happens after the round has left the barrel). Also, the barrel didn't need to be rifled, as the spin to the projectile was provided by the four off-center rockets.

Since Gyrojet weapons never became popular, manufacturing stopped in the late 1960s. Some weapons are still available as collector's items, but the bullets cost over $100 per bullet.