Firearm design question


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chris in va
December 31, 2012, 04:58 PM
Can't say as I've seen this discussed much.

We all drive vehicles that use the internal combustion engine. How feasible would it be to have a rifle use a 'gas tank' of sorts with a fuel injector in the chamber? Have a feeding mechanism for the projectiles, no primers, cases or powder.

Similar to an air rifle, but more powerful as it uses an explosive air/fuel mixture like a car engine.

I started thinking about this as relying on case, powder and primer availability gets annoying.

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rcmodel
December 31, 2012, 05:12 PM
I think the problem would be the same one presently stopping the caseless ammo sporting and military small arms that keep getting invented, and keep hitting dead ends.

You have to have a way to open the chamber to put the projectile in it.
(Unless it's a muzzle loader.)

Then the problem becomes sealing the combustion chamber without the expanding brass case to do it with.

Then there is also the problem of heat build-up.
The empty cases carrying away heat is one of the other things they do.

Propane potato (spud guns) do work on the same principal you suggested.
But they are muzzle loaders.

And then we also have CLGG combustion light gas guns.
http://en.wikipedia.org/wiki/Combustion_light_gas_gun

rc

xfyrfiter
December 31, 2012, 05:30 PM
Some construction tools [staplers. Nailers] and the like, already have a gas cartridge activated by piezo spark, all self contained and capable of multiple shots. The industry has been using these for a number of years to eliminate the necessity for an air compressor. The nail is propelled by a piston with a hardened face. Add a rifled barrel and lead projectile and there you go. Totally illegal but possible.

txnative1951
December 31, 2012, 06:06 PM
The military has used electrically fired primer systems on certain larger weapons over the years. On 16" guns of the Iowa class battleships, the primers were a separate mechanism that were loaded last and if it failed to ignite, it could be easily replaced without necessitating the reloading of the entire chamber. Initially, these guns used chemical primers (similar to what we currently used, but super sized), but I believe that some were retrofitted in later years to use an electrical primer system. I also believe that an electrical priming system has been in use on large multi-barrel systems that the military uses (e.g. the 30mm and such). Remington came out with the Etronix system awhile back and it consists of a somewhat conventional primer that is sensitive to an electrical charge instead of a mechanical impact.

With respect to using the idea of a air-fuel mixture that is fed into the chamber for the propellant to the bullet, I have to think that you would need an O2-fuel mix instead. There is also a question of energy density.

holdencm9
December 31, 2012, 07:33 PM
I think part of the problem would also be the potential energy in a relatively-small cartridge versus the energy stored in whatever gas you were thinking of. I made a spud gun once with a 4" diameter x 16" long chamber, and it would shoot a spud about 250-300 fps, but that essentially added up to energy of 9x19. So, not much, unless you use some really exotic (read: dangerous) combustibles. Therefore I think the power you could get out of such a concept would be relatively low.

As RC mentions, the trickiest part is opening the chamber to insert a new bullet and also allow oxygen in, and then squirt some fuel in there with a tight-enough seal to ignite reliably.

If you go to this link, one guy has an idea for such a semi-auto combustion spud gun. Crude drawing, but you get the idea, and the general consensus seems to be....that will be tricky!

http://www.spudfiles.com/forums/semi-automatic-combustion-cannon-concept-t24113.html

As a side note, in about the 12th post of that link, is an idea for a "cartridge-fired" semi-automatic spud gun, essentially bringing us back full circle to brass, powder and primers.

MachIVshooter
December 31, 2012, 07:39 PM
liquid propellants are already being used in artillery; they're able to precisely meter each charge for the desired trajectory. This is a very useful capability with indirect fire weapons, but not so much with small arms. It also doesn't lend well to high rates of fire.

As rcmodel noted, the caseless ammo concept has been plagued with problems. Though HK actually did manage to make a functional and decently reliable caseless cartridge assault rifle after many years and many failed prototypes, ultimately, it's just not feasible. Gas or liquid propellant small arms will suffer from some similar problems to the caseless rounds, and some different ones. One of the biggest dangers would be volatility; a tank holding 600 rounds worth of propellant is going to make quite a bang if it gets ruptured and ignited, where metallic cased cartridges are very difficult to ignite and do not tend to propogate.

holdencm9
December 31, 2012, 07:42 PM
Some construction tools [staplers. Nailers] and the like, already have a gas cartridge activated by piezo spark, all self contained and capable of multiple shots. The industry has been using these for a number of years to eliminate the necessity for an air compressor. The nail is propelled by a piston with a hardened face. Add a rifled barrel and lead projectile and there you go. Totally illegal but possible.

That mechanism works well to drive an object a very short distance, but I imagine would not work very well to drive a projectile a long distance accurately. And then you still have the power issue. Even a pretty powerful nail gun is probably only a fraction of the kinetic energy of a service-caliber gun.

Anyway, the way I see it, the piston would hit the bullet and force it into the bore, but I don't think the bullet would have enough momentum to force its way through and out of the bore, so it would just get stuck. Usually what keeps the bullet moving is the build-up of pressure from the expanding gases in the cartridge.

MachIVshooter
December 31, 2012, 07:47 PM
Even a pretty powerful nail gun is probably only a fraction of the kinetic energy of a service-caliber gun.

The most potent hand-held nail drivers are the .27 caliber powder acutated tools for driving heavy gauge nails into concrete and steel. They use a stubby rimfire blank with slightly less charge than a .32 ACP.

Deus Machina
December 31, 2012, 09:11 PM
See the Tippman C3, (http://en.wikipedia.org/wiki/Tippmann_C-3) a propane-powered paintball marker that worked on that exact principle.

It worked, and it worked well enough. The market is what kills.

Aside from that, include a way to open the breach and clear a jam, and it's feasible. It's just not nearly as convenient and failsafe as self-contained cartridges, and even reasonably slow rates of fire (notice the C3 is pump-action) build up heat fast.

Part of the issue with the caseless firearm designs was heat. A brass casing absorbs heat, but doesn't have much time to transmit it to the receiver before it's ejected. So it works as a heat sink that is very inefficient in service, but very efficient for the space.

pseudonymity
December 31, 2012, 09:41 PM
I imagine there are self oxidizing liquid propellants that are suitable at outdoor temperatures and atmospheric pressure, nitromethane comes to mind for one. I would imagine two issues to start - the first is how to meter the mixture reliably for the projectile used. Different powder charges mean changes in velocity which means different trajectories. I would think the problem would only be more difficult if you had to measure the propellant charge on the fly. The other problem is the control of the flame front. Powders are constructed with different shapes and coatings to make them burn at a specific rate, but I think that a liquid or liquid/gas mix would be more difficult to get a precisely controlled burn rate and corresponding pressure curve.

WardenWolf
December 31, 2012, 10:12 PM
See the Tippman C3, (http://en.wikipedia.org/wiki/Tippmann_C-3) a propane-powered paintball marker that worked on that exact principle.

It worked, and it worked well enough. The market is what kills.

Aside from that, include a way to open the breach and clear a jam, and it's feasible. It's just not nearly as convenient and failsafe as self-contained cartridges, and even reasonably slow rates of fire (notice the C3 is pump-action) build up heat fast.

Part of the issue with the caseless firearm designs was heat. A brass casing absorbs heat, but doesn't have much time to transmit it to the receiver before it's ejected. So it works as a heat sink that is very inefficient in service, but very efficient for the space.

The main problem was indeed heat buildup. People found it melted itself internally with heavy use, and paintballs would sometimes come out flaming. Tippmann was going to try to make a semi-auto version of it, but they gave up. The heat buildup made it impossible. There was also the real risk of it being regulated by the ATF as a Destructive Device, as it would technically be a firearm firing a projectile over .50 in diameter rather than an airgun.

This is why we don't have caseless combustion guns: heat buildup, and the amount of weight that a cooling system would cost would make it impractical.

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