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Ramjet ammo

Solid fuel integrated rocket ramjet minaturized to the size of a bullet
  (+10, -3)
(+10, -3)
  [vote for,

A ramjet, sometimes known as a stovepipe jet requires virtually no moving parts. Indeed, if it uses solid fuel, the heat of the air flowing into it ablates the fuel, and no moving parts are necessary. The main problem with ramjets is getting them up to the speed where they function.

In theory, it might be possible to minaturize such a ramjet down to the size of a M-60 grenade, shotgun shell, or perhaps even a .45 round. In practive military artillery would likely be the first weaponry it would work with.

Such a small engine could then be fired out of the gun to get up the initial speed needed for the ramjet to begin operation. To avoid jamming the exhausts, a sabot would likely be needed, and this might function as a parachute later on to pull an ignition on the engines. The ramjet would then greatly increase the velocity of the projectile. If the outlets were slightly canted, this might also continue to impart spin on the projectile, which may provide gyroscopic stability during flight.

Such projectiles could be fired from existing weapons, and might increase range, velocity, or both.

I forsee applications in a number of fields: Signal flares are an obvious choice, as individual rounds are already expensive, accuracy and secrecy is of little importance, but distance is considered highly desirable.

More exacting design standards could allow these weapons to be useful in armor piercing rounds, and in larger ammunition, they might be capable of penetrating tanks with an explosive round, thus replacing heavy and expensive bazookas with somewhat smaller and cheaper guns that could be easily used for at least a few other applications as well.

CWIS weapons systems, currently used to defend ships against missiles might also benefit greatly from longer range bullets, although I am not sure whether the reduction in weight of the ammo would be worth the range increase. Usually when the aim is to defend against missiles, cost is not much of an issue.

Lastly, if they could be produced cheaply enough, these might make for far more deadly antipersonnel weapons. The jet ports would heat the projectile, and hollow it out, making deformation and fragmentation of the projectile upon impact more likely. Since the jet ports would provide stability in flight, but clog upon impact this feature would also tend to favor causing the projectile to tumble around once inside the body. Elite forces might find this to be quite useful on high-risk missions.

Ramjet ammo would likely be quite expensive, and therefore of limited usefulness in many fields. However, unlike gyrojet ammunition, these could be used in existing guns, making their adoption or rejection much cheaper on any group who should choose to experiment with them.

ye_river_xiv, Dec 17 2006

I didn't do too well with a similar idea Hypersonic_20bullet
[ldischler, Dec 17 2006]

The Gyrojet http://en.wikipedia.org/wiki/Gyrojet
Rocket propelled small arms rounds [oneoffdave, Dec 17 2006]

Roger Ramjet http://www.youtube....watch?v=dZIjT3S7wvc
Inventor of the ramjet. His original name was Ranjet, which he anglicized around the same time he dyed his hair red. [bungston, Nov 03 2008]

Albert Fonó's ramjet artillery ammo proposal, 1915 https://en.wikipedi...et#Albert_Fon.C3.B3
As mentioned in my anno. [notexactly, Jan 13 2016]


       I like the flare gun idea. It could also be used for fireworks.
caspian, Dec 17 2006

       It's an interesting thought. If you can deal with the deformation of the projectile on launch and rifle spin it fast enough to keep a forward alignment, this could work.   

       Way to go making the world more lethal.
BunsenHoneydew, Dec 17 2006

       In most cases, I think increasing the velocity of the projectile would not improve lethality.
BJS, Dec 17 2006

       // In most cases, I think increasing the velocity of the projectile would not improve lethality. //   

       So if I hit you with a baseball at say 5 mph and 95 mph the effect of both would be about the same? I am guessing you would not want to be the subject in this experiment.
Chefboyrbored, Dec 17 2006

       Ah, but what if you increased it from 1000 mph to 4000 mph? There aren't degrees of deadness.
ldischler, Dec 17 2006

       In the cool light of morning, I'm thinking the whole thing may be useless.   

       //In most cases, I think increasing the velocity of the projectile would not improve lethality//   

       This is true, but velocity is a major factor when distance and penetration are prime concerns, such as in launching signal flares, and/or armor piercing rounds.
ye_river_xiv, Dec 17 2006

       Speed does make a difference. Being hit by a .22 caliber assassins pistol is a very easy way to get dead. The bullet enters but has insufficient velocity to exit and so bounces around inside. Being hit by a 22 caliber M16 round means you have a neat round little hole that simply zips on through and is survivable. The design of the bullet has more to do with the speed. a 357 hollow-point is much more lethal than a 357 full metal jacket.   

       On the far side of the extreme is the fact that once sufficient velocity is achieved you start to get into Kinetic energy damage(exceedingly small projectile traveling at exceedingly high velocity will vaporize someone) I'm not sure that the velocity of this bullet is in this range.
jhomrighaus, Dec 17 2006

       //a 357 hollow-point is much more lethal than a 357 full metal jacket//

Which is why the military uses the full metal jacket. It's more humane! Or it used to be, before ballistic jackets.
ldischler, Dec 17 2006

       Didn't the Gryrojet range of weapons attempt this?
oneoffdave, Dec 17 2006

       //So if I hit you with a baseball at say 5 mph and 95 mph the effect of both would be about the same?// We are talking about bullets being shot out of guns at incredible speeds and not baseballs which are throne.
BJS, Dec 17 2006

       royally throne I betcha?
jonthegeologist, Dec 17 2006

       /Besides any increase in speed is paid for by a decrease in mass upon arrival./   

       Energy imparted increases as the square of velocity, so it not a pure tit for tat. Faster = more wallop. This might make a difference against an armored target like a tank.
bungston, Dec 17 2006

       The exhaust of this will leave a nice trail pointing back to where the shooter is, so not the most discreet of weapons
oneoffdave, Dec 17 2006

       //The exhaust of this will leave a nice trail pointing back to where the shooter is, so not the most discreet of weapons//   

       Gyrojets didn't seem to have a serious problem with that, and it is no concern at all with tracer rounds or flares.
ye_river_xiv, Dec 18 2006

       Missiles seem to fly straight. Maybe it is the fins.
bungston, Dec 18 2006

       If this could be baked maybe it could be used to steer the projectile after firing. I guess this is a quarter baked idea.
pydor, Dec 19 2006

       The Gyrojet round has canted exhaust ports that impart spin to the round, giving it stability.
oneoffdave, Dec 19 2006

       [Gyrojet @ wikipedia]   

       //They are, however, rarely fired; ammunition, when available at all, can cost over $100 per round. ... principle was also examined for use in survival flare guns .. flare version [] was used for many years as a standard USAF issue item in survival kits ... had an effective altitude of over 1500 feet(300 meters). ... It was quite effective.//   

       It's still not a ramjet though, so [+] for originality
BunsenHoneydew, Dec 19 2006

       I've had some experience with military excess spending, and I assure you that 40 dollars a round would not make them bat an eyelid... especially if those rounds could be put in standard issue firearms, and take out tanks, helicopters, or other targets which normally require a rocket launcher. Part of the Gyrojet's failure was that it required all new guns. The other part was that it wasn't useful at close range.   

       The idea here, is to create a round that can be fired from existing weapons, such as the standard-issue 12 gauge shotgun, and m-60 grenade launcher. If minaturization allows, a .45 ACP round might also be in the works. Most of these guns are already used by various forces for some purpose. The shotgun, in particular, is almost universal, but has a maximum effective range of about 150 yards. the Military already wants that extended to 200, although the added range is only useful in limited situations. Getting that extra 50 yards using special ammo, rather than revamping an entire military of guns might make sense. Additonally, if piercing worked, being able to carry a few extra shotgun shells and your normal, or one extra shotgun would be a lot nicer than having to lug around a whole bazooka.   

       I'm still not too convinced that my own idea would actually work, and I forsee a larger market for it in "terrorist" groups, but it may still bear some consideration.
ye_river_xiv, Dec 24 2006

       To assure function you would be entering the realm of smart bullets (check out some Vernor Vinge) or some version of fly by wire/laser/etc.
normzone, Dec 24 2006

       Ideally, such devices would be unnecessary. As much as I enjoy Chris Roc's bullet control plans, expensive ammo doesn't generally find much of a market.   

       Some sort of sabot would probably be needed to keep the hot gas which propels the ammo out of the gun from going backwards through the engine. The barrel of the gun would also likely need to be rifled, and hopefully, the ammo could have sufficient spin imparted to it that it remained oriented correctly once out of the barrel, since it would likely need to get out before any ramjet system would work.   

       There may be a non-electronic way to initiate the burn. A string tied to the sabot, so that when the sabot falls far enough away, the ammo gets ignited, thermally induced firing, or perhaps the friction of the air going through it would suffice. If not, this probably would be of no economical use in small arms.
ye_river_xiv, Jan 02 2007

       I don’t foresee a bullet taking out a tank anytime soon, unless the bullet is going very fast and is very big. Current tank killers are moving about 4 km/sec and about a kilo in mass. Some times they make it through, some times they don’t. Don’t get me wrong, [+] for the idea. I like it, but its actual application would most likely be sniper.
MikeD, Nov 03 2008

       //Current tank killers are moving about 4 km/sec//
That fast? Are you sure? (Not to question your expertise or anything, but that's approaching Mach 12.)
If you want to go really fast, you want either a railgun (recently demonstrated at Mach 7) or a Ram Accelerated Projectile system (theoretical top speed is orbital - 7km/s (Mach 23) or so).
neutrinos_shadow, Nov 03 2008

       Explosive Formed Projectiles, [Neutrino]. Relatively cheap and easy to make. They can be horrifyingly effective.
MikeD, Nov 03 2008

       //Explosive Formed Projectiles, [Neutrino]. Relatively cheap and easy to make//
Don't try this at home, children.
coprocephalous, Nov 04 2008

       //The US military stuck them in the nose of the A-10//
No, they didn't "stick them in the nose". They built an aeroplane around the Avenger.
The GAU-8 is about 40% the length of the A-10.
AbsintheWithoutLeave, Nov 04 2008

       "Trommsdorf-granaten" were Baked during the 39-45 European Difference of Opinion (The difference of opinion being that the Germans thought they should rule the planet, and others disagreed).   

       It sort-of worked, but was too inaccurate to be useful.
8th of 7, Nov 04 2008

       Actually I meant have the propellant in the cartridge put a twist on the bullet: back of the bullet is corckscrew shaped,
FlyingToaster, Nov 04 2008

       [MikeD] - ah, EFPs. Forgot about those.
I stand corrected.
As you were.
neutrinos_shadow, Nov 11 2008

       Century-old prior art! I was reading about ramjets the other day, and it turns out ramjet ammo for artillery (though presumably not SFIRR) was proposed in 1915, just two years after the invention of the ramjet: [link]
notexactly, Jan 13 2016


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