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Old June 3, 2017, 09:57 AM   #1
TXAZ
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Fastest possible bullet in theory?

What is the maximum possible speed of a bullet, given an ideal (trying to keep it easy):

A very small projectile (near zero mass)
A large amount of propellant (whatever that may be)
A perfect seal between the bullet and the barrel
Zero resistance between the bullet and the barrel
There is no barrel twist

All energy in the gunpowder is converted into forward kinetic energy

Is the maximum theoretical speed of the bullet the same as the speed of the burning wave front?

Thanks in advance.
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Old June 3, 2017, 10:47 AM   #2
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Is the maximum theoretical speed of the bullet the same as the speed of the burning wave front?
If you can remove all friction, so that all the energy goes into propelling the bullet, then in theory, you would get CLOSE to the speed of the powder gas.

Close, because even if you could remove all friction, you can't remove the inertia of the mass of the bullet. It will take some energy to accelerate the bullet from rest.
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Old June 3, 2017, 06:28 PM   #3
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I believe the M1 Abrams main gun uses fairly standard propellant. It achieves a muzzle velocity between 5000 and 6000fps.

That is done with a smoothbore barrel and a sabot round so it's not exactly comparable to a rifled barrel firearm.
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Old June 4, 2017, 08:58 AM   #4
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The German WWI Paris gun still holds the record for a conventional "practical" gun (practical in a limited sense, they achieved the speed by using a set of steadily growing rifling rings to make up for excessive barrel abrasion).
You can achieve much higher velocities with a light gas gun. In it a conventional charge compresses a hydrogen or helium gas to very high pressures, and it's fired by a burst disc releasing the pressure. You can get up to 25,000 ft/s that way.
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Old June 6, 2017, 12:48 AM   #5
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I have read that the shock wave from smokeless propellant travels at just over 6.000 fps, so that would be your theoretical limit using conventional propellant. People have hit around 5,400 fps in 22 centerfire rifles.
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Old June 6, 2017, 11:25 AM   #6
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The Germans were working on some type of large bore, long barreled cannon that had "Boosters" at various stages of the tube. I never had enough interest in cannons to read the rest of the article to see how it worked out.
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Old June 6, 2017, 12:38 PM   #7
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Abrams main gun gets there with the DU penetrator of an APFSDS round only. The General Dynamics KEW-A1 has a muzzle velocity of 1,740 m/s (5,700 ft/s).
The issue with rifle bullets is mostly the bullet. A lead cored bullet cannot get going too fast due to the heat created melting the core. A solid is a different story though. You still run into instability caused by heat. I seem to recall some guy playing and got around 5,000 plus fps. Forget where or who though.
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Old June 7, 2017, 10:09 AM   #8
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I think you've gotten your answer for conventional "gunpowder".

Railguns produce higher velocities using non-conventional propellants but it's really beyond anything that's on our horizon as individuals.

Sabot rounds (including tanks' main guns) get very high velocities simply because the projo is light for caliber. But then they discard their sabot and fly like normal, or even long for caliber rounds outside the barrel. That is technology that we should be able to use in small arms right now. It's probably just a matter of time before someone makes this work well and puts a lot of conventional HV rounds in the shade.
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Old June 8, 2017, 09:49 AM   #9
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Fastest possible in theory is the speed of gunpowder expansion minus the energy required to overcome inertia minus loss to friction. The problem becomes that in reality, as bore size decreases friction increases (why you have to pump harder to get the same amount of water through a smaller pipe than a larger pipe), so you are left with trying to find the right compromise of bore diameter to chamber volume.

Because chamber volume...as it increases you can put more powder in it, but in order to not destroy the firearm it must burn slower, so in order to harness more of the potential energy the barrel must be made longer....

So to get more velocity, engineers try tricks like discarding sabots to get the decreased friction and energy transfer of a large bore, but with a projectile mass of a smaller bore. Or they try to use a squeeze bore where the projectile starts out one diameter, and is then reduced in diameter to get an increase in velocity like going from a big hose to a small hose (same volume into a decreased diameter pipe equals more velocity).

In practice, WWII era squeeze bore anti tank guns got into the 4,600 fps range, and as already stated the 120mm smoothbore cannon can get up to 5,700 fps.

At this point tank gun designers (unless they are German then it is Panzer kanone designers) aren't trying for more velocity, but more mass. Rheinmetall is working on a 130mm gun and the US military flirted with a 140mm gun, the Russians seem to be sticking to the 125mm bore for now. And essentially everyone has abandoned the squeeze bore concept for the time being.

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Old June 8, 2017, 10:31 AM   #10
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Sabot rounds ... That is technology that we should be able to use in small arms right now. It's probably just a matter of time before someone makes this work well and puts a lot of conventional HV rounds in the shade.
Remington Accelerators.

done decades ago!!!

4000+fps from a .30-06!!

55gr .224 bullet in a plastic sabot, made in .30-30, .308 Win, and .30-06. No others that I know of. Haven't seen any in ages, I think Remington stopped making them a while back.

Turned the .30-30 into a .222, the .308 into a .22-250, and the 06 into something that beat out the .220 Swift for velocity.

The idea was to be able to turn your average deer rifle into a varmint rifle, simply by changing ammo. It didn't work well. Accuracy was the big problem. Most rifles grouped them ...poorly.

A few (apparently only a very few) would shoot them as well as they shot regular "deer" loads, and nobody's really happy with a minute of deer varmint rifle. And then there were complaints about plastic fouling, as well.

The 120mm cannon gets around the fouling issue by being smoothbore, and tank sighting systems are just a bit more refined and complex than what we usually mount on a rifle. And I would assume that minute of tank at 2000 meters is just slightly different from MOA at 100.

The key to sabots in modern small arms isn't getting something that works, its getting something that works WELL, (meaning high velocity AND accuracy) and so far, no one has.
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Old June 8, 2017, 12:39 PM   #11
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Also, tank guns have a little "tooth" at the muzzle to initiate the controlled disintegration of the sabot. Rifle sabots need to disintegrate on its own, adding an additional degree of complexity.
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Old June 8, 2017, 04:57 PM   #12
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Remington Accelerators.

done decades ago!!!
Yep. Never tried them but some people said they shot as well as the rifle in question would shoot normal ammo. That is probably the best case scenario. And as you say, most deer rifles do not have varmint rifle accuracy.

But Remington only tapped half the potential, the other half being long, probably fin stabilized bullets. Long range shooting and long bullets are highly popular today and the ultimate development AFAIK would these miniature tank guns.

I don't know if such a system can be made to work for commercial use and at a non-government price. IIRC 120mm sabot rounds are well over $1000 apiece and that includes steel training rounds.

If we are ever going to see it, it will probably be in military use first. There is the .50 BMG SLAP round but that is basically a bigger "Accelerator" needing a rifled barrel.
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Old June 8, 2017, 05:15 PM   #13
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I believe in the 1920's there were experiments with swage bore weapons that pushed projectiles up to 6000 fps. These barrels got smaller by a considerable amount as the projectile approached the muzzle. I recall that bore life was horrible.
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Old June 9, 2017, 06:20 PM   #14
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The Germans made some pretty effective light and medium anti-tank guns based on that concept during WWII, especially a 28 -> 20 mm. Luckily for the US they didn't have enough tungsten for the rounds, and didn't know about using uranium (depleted uranium rounds haven't been invented yet).
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Old June 9, 2017, 06:31 PM   #15
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didn't know about using uranium (depleted uranium rounds haven't been invented yet).
WE didn't know about using depleted Uranium as a projectile, until several decades after we first created depleted Uranium in 1945.
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Old June 11, 2017, 05:04 AM   #16
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Old June 13, 2017, 12:49 AM   #17
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Probably the best known "squeeze bore" sporting rifles were those made in Germany in the 1930's by Halbe & Gerlich (who combined their names into "Halger" which they used as a trade name for a high velocity rifle. The idea was to make the inside diameter of the barrel tapered so that the pressure increased as the bullet was reduced in diameter. IIRC, the bullet was not really "squeezed" down, because that would distort it, but a sort of "skirt" was used to allow the bullet to pass through the barrel as the hole became smaller. The idea worked, but the cost of making the special barrels was too high to be practical in a sporting rifle. It was later used in tank and anti-tank guns, though, and gave reasonably good performance, but was superseded by shaped charge projectiles which did not require high velocity to penetrate armor.

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Old July 12, 2017, 03:58 PM   #18
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Quote:
TXAZ wrote:
What is the maximum possible speed of a bullet...
The maximum possible speed of a bullet in ballistic flight in air is the speed at which heating caused by air resistance and other aerodynamic forces destroy the projectile. So, the answer is, "It depends on the projectile".
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