Max Chamber Pressure

[Flechette]

I saw a video of some of the nasty tricks the CIA can do in asymmetrical warfare. One was to sneak ammo loaded with explosives into the enemies supply chain. When a shot is fired with the planted round it will destroy the weapon and sometimes kill the user.

The video showed someone firing an AK with such a round. He lived but the gun was destroyed.

It got me thinking, could a gun be designed to handle such chamber pressures? If so, what would the muzzle velocity be? One potential benefit would be radically smaller cases (think a 5.56 NATO the size of a .22 WinMag).

Someone must have looked into this.

 

[Sentryau2]

I dont know, its possible but it would have to be much thicker and heavier. Weigh all ammo, there has to be a weight difference, or take it for components and reload it only if the powder, looks and burns good.

 

[Gtscotty]

You're talking about using a material that undergoes honest to god detonation versus deflagration to propel the projectile? That concept has popped into my mind from time to time too, I think I read that the theoretical maximum velocity (given no bullet friction) possible from smokeless powder is around 5300 fps. If you were to use an explosive like RDX with a detonation velocity of over 28,000 fps, as your "powder", there's no telling what muzzle velocities you could attain.

I'm sure that, as Sentryau2 suggested, the real trick to using a propellant like that would be keeping the gun in one piece. Maybe someday, they'll figure out how to use shape charges or explosive lenses, or something similar to make the concept possible without having to replace your firearm after each shot.

 

[Slamfire]

Explosives are good for shattering rocks, don't think metals would hold up very well.

Someone tried it, found it did not work, and it has been so long ago, no one remembers.

 

[Jim Watson]

The usual trapped ammo left out for VC to find was loaded with a case full of Bullseye or other pistol powder, maybe blank powder if they could get it. The urban legend that they were filled with C4 does not work because a cartridge primer won't initiate RDX.

The propellant for the H&K G11 was reportedly an explosive compound somehow denatured to develop no more pressure or shock than the action could stand, but better suited to being molded into a caseless charge than NC-NG-NG.

The early smokeless powder Ballistite was developed when it was found that nitroglycerine and nitrocellulose would moderate each other into the propellant range. Previous attempts to use guncotton (straight nitrocellulose) blew up a lot of guns. Eventual nitrocellulose powders had less than the maximum degree of nitration so they "burned" (deflagrated) instead of exploding.

 

[rcmodel]

Actually, the CIA had nothing to do with it.
Project Eldest Son was carried out by Army SOG personnel during the Vietnam war in 1968.
And the cases were filled with a sensitive PETN type high explosive that could be set off by the primer.

The key is not an increase in chamber pressure, but rather a high explosive is used.
The resulting detonation shock wave shatters the weapon, regardless of how heavy or strong it is built.

But regardless of all that?
The strength of a modern firearm is not the limiting factor.
The brass case that acts as the chamber seal is the limiting factor.

If the case fails, high pressure gas is released into the action, and that will take the path of least resistance to the atmosphere.
That in turn distroys even the strongest action.

The other limiting factor is the burn characteristics of smokeless powder.
Fast burning powder is unable to produce truly high velocity.

So, a larger charge of slower burning powder is used in high-velocity rifle cartridges to produce a longer pressure curve to accelerate the bullet down the barrel over a longer distance.

Using a faster powder at higher pressure would not result in the more gradual acceleration necessary to get a bullet moving at up to full rotational speed in the rifling.

rc

 

[Flechette]

Doesn't the cannon on the M1 and Leopard tanks throw DU darts at 5200 fps?

Quite the engineering feat!

 

[rcmodel]

Yes.
But they use a sabot of full caliber (120 mm smoothbore barrel) to push a relatively small diameter dart at high velocity.

http://en.wikipedia.org/wiki/File:M829.jpg

It would be impossible without the large surface area of the sabot for the pressue to push on.

rc

 

[HOOfan_1]

Smooth bore supposedly gives a better seal too

 

[Flechette]

Explosives are good for shattering rocks, don't think metals would hold up very well.

Someone tried it, found it did not work, and it has been so long ago, no one remembers.

As a thought experiment, what if someone made a barrel and a breech out of a 1ft/1ft/1ft block of stainless steel. If you then placed RDX into a 22 WMag, how fast would it come out of the barrel?

 

[rcmodel]

In theory, it would be going 28,700 FPS.

That is the velocity of the shock wave from an RDX explosion.

In actual practice, the bullet would be vaporized before it could move out of the way.

rc

 

[jakk280rem]

So in order for a projectile to survive the initial blast and its trip down the barrel it would need to tough, right? So tough it would destroy the barrel in short order? I think high tech materials would make it possible. But in the end you would end up with a 200lb, $500,000 rimfire that cost $200 per shot. Might make a cool varmint rifle.

 

[Sentryau2]

EFP bullets instead of standard case designs, use a very small barrel instead of something like a standard barrel only big enough to hold the case....so its really more of a launcher. SWIM Plays with EFP's sometimes. Just thought of that.
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1ap/hmtd/rdx ))
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Think of flying metal hole punch, EFPs are used against armored vehicles in ambush situations. Unlike shaped charges they do not have to be set off at an ideal "stand off" distance and can instead be detonated a ways away from the target and still penetrate HRA, half the diameter of the disk depending on its material (swim thinks pig iron or mild steel is the best thing to use)

 

[DanTheFarmer]

Re: The 1 x 1 x 1 block of metal to make a breech and barrel.
Take a look at some Civil War era "Coastal" or "Heavy" mortars. They were about as big in diameter as they were long (that's only a slight exaggeration). They were nothing like the field mortars of WWII and later times. They had an enormously thick breeches to contain the pressure during firing. Modern propellants spread out the pressure curve and reduced the maximum pressure while increasing the total pressure, thus allowing less massive guns to work.

Re: 120mm smoothbore sabot rounds. Sealing may be an issue. Ripping the rifled driving band off at high velocities may be an issue as well. But the main reason they are smooth bore is to decrease the diameter of the penetrator. A rifled round needs to be spin stabilized and there a ratio between diameter vs. length below which the round doesn't fly well. You can throw spiral pass better with a football than a rugby ball but if you make the ball too "pointy" it won't work. A smoothbore round is fin stabilized and can have a smaller diameter, thus greater sectional density and penetrating power.

There were a few attempts to make a fin stabilized rifled tank round by having the sabot mounted on bearings so it could rotate during travel down the barrel while the penetrator remained unrotated but you can see this is getting complicated fast.

Dan

 

[mugsie]

Remodel, you hit it right on the head. I was in SF, and spent 68 & 69 in Nam. One of the things we did was to plant booby trapped ammo in caches we discovered. Typically we'd destroy most of the cache, but leave a little lying around, some of which was modified to explode. We did this with grenades, motor rounds, and of course ammo. Occasionally, we'd find a weapon that had exploded. I doubt a receiver could be made to withstand the pressures involved. This is one reason I will never use any ammo I find remaining at the range, as I never know what some sick person would do.

Stay well....

 

[torqem]

ballisticion Robert hutton, for G and A mag, years ago, got a 22 gallery bullet (sintered iron, 15grs or some such, to 6000 fps in a 22-284, I think it was (30 years ago, ok? ) So the 5300 might be the limit with lead cored, copper jacketed bullets, but it's not all that can be had with smokeless powder. He said that a vapor trail could be seen as the bullets flew, because they were disintegrating in flight. Also, impacts on paper targets (at 100 yds IIRC )showed that the bullets were fragmenting.

There's something called "paradox rifling", wherein the bore is smooth for all but a short segment near the muzzle. This would increase velocity potential, by reducing friction and chamber pressures. The Nazis drastically increased the velocity of their AA belt-feds, by building a restriction into the barrels, near the muzzle. A combination of these techniques might let you have a (very lw for caliber, hollowbased) bullet that achieves 6000 fps, but stays together/reasonably accurate. Certainly, it would have less barrel erosion at the "throat" of the rifling. It might need a steel core, or need to be made of solid copper, etc. dunno. But 5300 fps is not the max potential of powder.