Editing Gyrojet (section)

== Design ==
[[Image:Gyrogroup.jpg|thumb|right|The Gyrojet family: two Gyrojet pistols, a carbine and the rifle. In the top-right corner is a box of 13&nbsp;mm Rockets, and at the bottom is a diagram book for the guns.]]

The inherent difference between a conventional firearm and a rocket is that the projectile of a conventional firearm builds up to its maximum speed in the barrel of the firearm, then slows down over the course of its [[trajectory]]; the rocket continues to accelerate as long as the fuel burns, then continues its flight like an unpowered bullet. A bullet has maximum kinetic energy at the muzzle; a rocket has maximum kinetic energy immediately after its fuel is expended. The burn time for a Gyrojet rocket has been reported as {{frac|1|10}} of a second by a Bathroom Reader's Institute book<ref>
{{cite book |last1=Bathroom Reader's Institute |title=Uncle John's Endlessly Engrossing Bathroom Reader |pages=237–240 |chapter= Fabulous Flop: The Gyrojet |quote=...each rocket burned for {{citefrac|1|10}} of a second. That may not sound like much, but in that short time the rocket could travel a full 60 feet, gaining speed and power all the while. It was as if the gun barrel was 60 feet long instead of just a few inches.}}</ref> and as 0.12 seconds by "The 'DeathWind' Project".<ref>A ''Gun World Magazine'' article, sixth displayed page, as shown by "The 'DeathWind' Project" at http://www.deathwind.com/gunworld.htm.</ref>

A firearm's rifled barrel must be manufactured to high precision and be capable of withstanding extremely high pressures; it is subject to significant wear in use. The Gyrojet rocket is fired through a simple straight, smooth-walled tube of no great strength.

Accuracy is increased by [[gyroscope|spinning]] the projectile. This is achieved for a bullet by being forced against spiral [[rifling]] grooves in the barrel. A rocket does not have enough initial energy to allow stabilization this way. Spin stabilization of the Gyrojet was provided by angling the four tiny rocket ports rather than by forcing the projectile through a rifled barrel. Combustion gases released within the barrel were vented through vent holes in it. Spin stabilization is limited in accuracy as a targeting technique by the accuracy with which one can point the launching tube and the accuracy with which the orientation of the projectile is constrained by the tube. The technique requires the shooter to have a [[line of sight]] to the target.

The rocket leaves the barrel with low energy and accelerates until the fuel is exhausted at about {{convert|60|ft|m|abbr=off}}, at which point the 180-grain rocket has a velocity of about {{convert|1250|ft/s|comma=off}}, slightly greater than [[Mach number|Mach 1]], with about twice as much energy as the common [[.45 ACP]] round.<ref name="deathwind1">{{cite web |url=http://www.deathwind.com/review_2.htm |title=Review 2 |publisher=Deathwind.com |access-date=2009-07-20}}</ref> While test figures vary greatly, testers report that there was a [[sonic crack]] from some rounds but only a hissing sound from others, suggesting that the maximum velocity varied from slightly below to slightly above Mach 1.
[[File:Kinematik alleinstehende Raketenpatrone CC BY-SA 4.0 by Grasyl.svg|thumb|241x241px|Gyrojet bullet diagram]]
In 1965, the manufacturer of the pistol claimed 5-mil accuracy (about 17 MOA, or about 4.5 inches at 25 yards), worse than conventional pistols of the time.<ref>{{Citation |last=Smith |first=W. H. B. |author2=Smith, Joseph E. |title=Book of Pistols and Revolvers |year=1968 |publisher=Stackpole Company |pages=762}}.</ref> However, in later tests accuracy proved very poor; the difference seems to have been due to a manufacturing flaw in later production runs which partially blocked one of the exhaust ports, creating asymmetrical thrust that caused the projectile to [[corkscrew]] through the air.<ref name="dockery">Dockery, Kevin (2007). ''Future Weapons''. The Berkeley Publishing Group. {{ISBN|978-0-425-21215-8}}.</ref> The [[Military Assistance Command, Vietnam – Studies and Observations Group|Studies and Observations Group (SOG)]] of the U.S. military in [[Vietnam]] in 1967 saw an opportunity to try out one of the SOG's new developments,<ref name=":0">''SOG: The Secret Wars of America's Commandos in Vietnam'', John L. Plaster, p. 78.</ref> In one test, a rocket round punched through an old truck door and into a water-filled 55-gallon drum, almost exiting its opposite side. SOG men also test-fired it through sandbag walls and even tree trunks.<ref name=":0" />

About one thousand of the "Rocketeer" model pistols were produced; a few saw service in the [[Vietnam War]] and were featured in the [[James Bond]] book and movie ''[[You Only Live Twice (novel)|You Only Live Twice]]'', the [[Matt Helm]] film ''[[Murderers' Row (film)|Murderers' Row]]'', and ''[[The Man from U.N.C.L.E.]]'' novel ''The Monster Wheel Affair''. At about the same general size as the [[Colt M1911]], the Gyrojet was considerably lighter at only 22 ounces (625&nbsp;g), as the structure was mostly made of [[Zamac]], a zinc alloy. The weapon was cocked by sliding forward a lever above the trigger to pull a round into the gun; the lever sprang back when the trigger was pulled. The lever hit the bullet on the nose, driving it into the firing pin. As the round left the chamber, it pushed the lever forward again to recock it. The pistol lacked a removable magazine; rounds had to be pushed down from the open "bolt" and then held in place by quickly sliding a cover over them on the top of the gun. Reloading quickly was impossible.

Tests in 2003 claimed that the acceleration, rather than being constant, started at a high value and decreased, leading to velocities at close range which were not as low as expected, about {{cvt|100|ft/s}} at 1&nbsp;foot (30&nbsp;cm) instead of the calculated {{cvt|20|ft/s}}. The testers suggested that the (secret) manufacturing process was designed to achieve this effect.<ref name="deathwind1"/> However, independent analysis of those testers' own published data shows that their conclusions were incorrectly calculated. The projectile's acceleration actually started out low and continually increased over the bullet's measured flight.<ref>{{cite web |url=http://futureboy.us/blog/gyrojet.html |title=Gyrojet Ballistics |access-date=2013-02-04}}</ref>