The MBA Gyrojet was conceived by Robert Mainhardt and Art Biehl. They formed MBAssociates or MBA. First off, The gyrojet is not a firearm in the conventional sense. It's ammo was a 13mm stainless steel armor piercing rocket. Later models were made in 12mm to comply with civilian guns having a max of .50 cal. Both pistol and carbine versions were available in different finish/price levels.
The pistol (well use that for our purposes here) is about the same size as a Colt 45, but it is very light, about 22 oz. When holding it, the stamped steel/alloy construction combined with all the vent holes make you feel as if this were a toy and incapable of holding up to the pressure of being a firearm. Well, you're right, because the Gyrojet isn't a firearm in the conventional sense.
When a conventional gun is fired, all the pressure from the exploding powder is held in the chamber/barrel. This pressure is what pushes the bullet forward and why as soon as a bullet leaves the barrel, it starts loosing velocity.
The Gyrojet round is pushed by burning solid rocket propellant that is contained within the projectile, so therefore all the pressure is contained by the "bullet" and not by the gun. This also means that muzzle velocity/energy sucks, about 860 ft/sec. Like most rockets however, the longer the burn, the faster the projectile goes. This means at about 100 yards, the velocity is screaming supposedly at 100 yards it is about 50% more powerful than the .45.
Loading/shooting the Gryojet is an experience. To load it, one slides the top cover of the receiver, pushed all 6
rounds in from the top and quickly slid the door shut again. there ew no magazine or feed lips like a semi auto, so all the rounds want to fly back in your face if you are not fast. For anyone familiar with the M-1 Garand, imagine trying to load it without the EN-Bloc clip to hold the bullets in place.
With rockets in place, the pistol is cocked for the first shot via a cocking lever that is pushed forward and down.
This lever is on the left side of the frame just above the trigger. The rocket leaving the barrel cocks the hammer for the subsequent shots. When the trigger is pulled, there is not the noticeable bang of a gun. The Gyrojet just makes a small crack then a hiss as the rocket goes off. Shake and open beer can to hear this noise.
Reports of the time show the gyrojet had some decent accuracy among those who tested (note: I have held these guns, but never fired one due to lack of 12/13mm rockets at my local Wal-Mart). Instead of conventional rifling, the Gyrojet used multiple angled exhaust ports to spin the projectile as it traveled thru the smooth barrel. this produced great accuracy, but it was also one of the downfalls of the design.
MBA originally produced this weapon for use in Vietnam, and that's where some of the downfalls were seen. Rocket fuel (solid type) didn't always like humid weather, so misfires or not getting a 100% burn was a problem, though an infrequent one. Another problem was the slight chance of fouling of the exhaust ports. Remember they provided the rifling, so a fouled port could cause a wobbling path and nasty accuracy problems. biggest drawback was that the rocket burning could leave a trail back to the shooter. Not good in combat.
After a thousand or so were produced, it seemed that the world was happy to stick with gunpowder. The Gyrojet disappeared, but due to its mention in war games like "Delta Green" interest is picking up in the real thing.
