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Old November 21, 2018, 04:25 PM   #1
TXAZ
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Maximum theoretical muzzle velocity?

When shooting the .50 BMG yesterday, we were discussing muzzle velocity: Lighter projectiles go faster with the same powder. Most of the .50 BMG bullets are 660 - 820 grains, moving at 2600-2800 fps at the muzzle.

A 15.5 grain Hornet NTX normally flies at about 3800 fps.
Question is, what are the limitations to getting a really light projectile to go really really fast, and how fast would that be?
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Old November 21, 2018, 05:40 PM   #2
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I found this online:

Quote:
Q. What is the highest velocity firearm?

A. The answer to that question depends upon whether we are talking about practical firearms or laboratory curiosities.

The theoretical maximum velocity attainable from normal commercial propellant powder and "conventional" loading densities is limited by the maximum velocity of expanding powder gases. Under ideal conditions this is stated as somewhere between 5700 f/s and 6000 f/s , and in conventional small arms between 4000-5000 f/s, by most authorities.
http://www.frfrogspad.com/miscellb.htm

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Old November 21, 2018, 11:26 PM   #3
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Hypothetically, the maximum velocity attainable by any projectile would be the same velocity of the gases from the expanding propellant as they leave the barrel. However, to achieve that feat, it would require laboratory conditions and systems set up to ensure the projectile can be accelerated up to such velocities. A typical 16" barrel does not offer the space necessary for such an acceleration.

Back in the 80's, NASA developed a theoretical method for interstellar space travel called the "Orion Project". The idea was to have a spacecraft that was built with a "magazine" loaded with dozens of small nuclear warheads. At the rear of the spacecraft was a massive metal 'pusher plate', designed to capture and absorb the force of the atomic blasts, transferring them into the overall momentum of the ship. As the spacecraft set sail, the bombs would be launched at timed intervals from the pod, whereupon they would detonate at a predetermined distance behind the ship. With each explosion, the ship would gain velocity. At a certain point, the ship would be accelerated to the same velocity as that of the matter expanding from the blast waves, making it the fastest manned vessel ever launched in human history. The Orion starship was calculated to be able to reach the Alpha Centauri system in just under 200 years, with the crew spending most of their time aboard in cryogenic hibernation.

Very interesting concept indeed, but there is this one question: How would you decelerate the ship now once it reaches it's destination? The only feasible solution would be to turn the entire vessel around via attitude-control jets, and explode a series of warheads, this time in the front of the ship. Which is going to force it, and it's crew to fly through a white-hot and extremely radioactive plasma smog of it's own exhaust. Not to mention the fact that the ship would also be forced to carry at least 100 times more mass than it was intended to be, due to the inverse square law of increasing mass versus the amount of fuel that would be needed to accelerate/decelerate at the same rate of speed. So, within a few years, research on this project was scrapped.

Now back to the subject of the maximum velocity of a projectile attainable under terrestrial conditions: Remember the news articles in the past about how suicidal individuals jumped off from very tall bridges and the subsequent autopsies on these individuals revealed that they actually died from the blunt force impact of STRIKING the water's surface and not by drowning? Air is not as dense as water but works the same way. When something travels fast enough, air would become so compressed ahead of it that it will act on the object as a solid state of matter. If a bullet can be accelerated to such a speed, it's interaction with this super-compressed mass of air ahead of it would destroy it. If it survives this force and manages to keep on plowing ahead, it will lose it's momentum very rapidly through the generation of heat, much akin to a spacecraft "burning up" as it reenters the Earth's atmosphere.

Target and varmint shooters who experiment with super-hot reloads in small caliber rifles often report that some of their bullets would "blow up" or fragment in midflight before reaching the target. Those are usually in the 3500-4100 feet/sec range. I do not know of any small arms cartridge that ever exceeded the low 4000 feet/sec range. Even with the hottest wildcat loadings. In H. Beam Piper's "Paratime" series of novels, one of the 2nd Level civilizations called the 'Akor-Neb', which has a penchant for dueling and settling disputes by assassinations, built pistols that "fired 10-grain plastic bullets at 10,000 feet/sec", and reportedly had no issues with overpenetration because the round immediately disintegrated upon impact, transferring all of it's energy into the target's body. In real life, such a bullet would have disintegrated as soon as it began moving forward in the barrel of the gun, when it meets that solidly compressed tube of air ahead of it. It might not even survive the detonation of that type of powder that would cause it to achieve such velocity. And I highly doubt any material on Earth can be built into a pistol that would withstand the pressures from the use of such a propellant, which would be akin to the detonation of a plastic explosive.

It would be a really interesting experiment if someone were to neck down a .50 BMG to accept a super-streamlined .17 or .22 caliber match bullet, and fire it from a standard-length rifle barrel just to see how it will perform. From a remote-controlled rig of course.

Last edited by Rachen; November 21, 2018 at 11:42 PM.
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Old November 22, 2018, 12:03 AM   #4
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Maximum theoretical muzzle velocity is only "theoretically" limited by the velocity gun powder explodes at. (That figure changes with advancements in technology) this is assuming you are using an action that can stand unlimited pressure.
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Old November 22, 2018, 02:49 AM   #5
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Quote:
Under ideal conditions this is stated as somewhere between 5700 f/s and 6000 f/s
This is my understanding as well. There are several caveats to deal with.
Quote:
Hypothetically, the maximum velocity attainable by any projectile would be the same velocity of the gases from the expanding propellant as they leave the barrel.
No, it has to be slightly slower than the accelerating gases in order to be pushed. Traveling at the same speed would cause pressure of the gases to be zero or the projectile's inertia to be zero. It would also entail a 100% efficiency reaction, and we know that is not possible.
Quote:
Target and varmint shooters who experiment with super-hot reloads in small caliber rifles often report that some of their bullets would "blow up" or fragment in midflight before reaching the target. Those are usually in the 3500-4100 feet/sec range.
That usually is caused by centrifugal forces ripping a lightly built bullet apart. I had that problem back in the 1970s with my 22-250. When I switched to a sturdier construction bullet, the problem disappeared.
Quote:
I do not know of any small arms cartridge that ever exceeded the low 4000 feet/sec range.
Just a few years ago, a 22 Middlestead launched a bullet just over 5,200 fps. It was recorder and supposedly verified. I'm sure if one person has done it, others have as well (that whole "scientific method", repeatability, etc, etc)
Quote:
It would be a really interesting experiment if someone were to neck down a .50 BMG to accept a super-streamlined .17 or .22 caliber match bullet,
During the 1950s and 60s, there was a lot of activity to be the first to break 5,000 fps. One famous attempt used a 378 Weatherby case with phonograph needles as projectiles. And it did not launch them as fast as hoped because of friction of the gas in the bore or the weight of the gases being pushed down a very small hole slowing the whole affair down. The hard part is finding that "sweet spot" where you have enough high pressure gases to push the bullet fast, but not so much gas that it slows it down.
Quote:
It would be a really interesting experiment if someone were to neck down a .50 BMG to accept a super-streamlined .17 or .22 caliber match bullet,
That has been done. The burning gases generated by the large powder charge weigh too much to achieve super-high velocities.
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Old November 22, 2018, 06:17 AM   #6
Art Eatman
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Velocity is limited by friction in the barrel and cannot equal the pressure wave propagation.
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Old November 22, 2018, 08:44 AM   #7
Jim Watson
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I recall an old Gun Digest article on cartridge collecting.
It showed the ".30 Medical Museum" made for simulating impact of high velocity shell fragments on cadavers and livestock. I don't remember the velocity numbers but it was a .30x.50 slightly shortened, presumably to match case volume to the powders available at the time.
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Old November 22, 2018, 09:47 AM   #8
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Velocity is limited by friction in the barrel and cannot equal the pressure wave propagation.
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"Theoretical", not actual. In theory we can eliminate friction. In practicality, we can almost completely mitigate its effects. With a long enough barrel and enough charges going off down that barrel (Nazi Super gun concept) we can push a projectile at near gas speed. It may take a 400 ft barrel and 125 powder charges.
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Old November 22, 2018, 01:33 PM   #9
Jim Watson
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In theory we can eliminate friction
Do they keep frictionless gun barrels in the Physics Department basement along with the cylinder of ideal gas and the other perfect simple machines?
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Old November 22, 2018, 04:29 PM   #10
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Quote:
In theory we can eliminate friction
The best way to carry out this experiment would be in space. A tube that is as long as necessary to completely burn all of the propellant provided, positioned far above the atmosphere so the effects of even the most random air molecules would not be of any concern. To FULLY eliminate any residual friction, the tube would have to be superconductive, with the projectile suspended in it's middle portion via magnetism. There would have to be a way to continuously burn propellant until detectors analyzing the departure of the bullet notices that the propellant gases and the bullet itself are both traveling at the exact same speed. And now, your experiment would be as near perfect as it can be.

Anybody want to venture forth a guess as to how much US Currency such a rig would cost to build, launch, stabilize, assemble, and then test? I am estimating at least 40 million dollars or more
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Old November 22, 2018, 06:10 PM   #11
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Originally Posted by reynolds357 View Post
"Theoretical", not actual. In theory we can eliminate friction. In practicality, we can almost completely mitigate its effects. ...
No. That is incorrect. You’re thinking “ideal”.
Theoretical considers known factors.
“Ideal” is eliminating factors by setting the environment in outer space, for example.
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Old November 22, 2018, 06:27 PM   #12
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Theoretical assumes ideal. If there is no assumption of ideal, you would use actual and not theoretical.
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Old November 22, 2018, 09:16 PM   #13
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well, if you can eliminate all the real world factors, then wouldn't the final velocity be just below the speed of light? E=MC2, ??

So at the speed of light, your mass becomes energy...so you'd have to stop while you still had mass, right?

now here's a question, would a bullet fired from a gun moving just below the speed of light achieve warp??
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Old November 22, 2018, 10:21 PM   #14
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That has been done. The burning gases generated by the large powder charge weigh too much to achieve super-high
Holy cow Scorch! I thought I was the only one with that wild idea. I have heard of the phonograph needle experiment before, must have been a pretty new challenge for the makers of THAT particular barrel, especially when the time came to put rifling grooves into it.

Quote:
That usually is caused by centrifugal forces ripping a lightly built bullet apart. I had that problem back in the 1970s with my 22-250. When I switched to a sturdier construction bullet, the problem disappeared.
The problem bullets were the jacketed ones, weren't they? Or to put it more accurately, jacket bonded to lead core? Heard from other shooters about the jacketed rounds coming apart at high velocity, but no problem with homogenous solid slugs.

Quote:
now here's a question, would a bullet fired from a gun moving just below the speed of light achieve warp??
It might not achieve warp, but what that bullet traveling at 99.999% of the speed of light CAN achieve??? Well to put it in shorter terms, if it were due to strike Jupiter, and you are on an observation station on Mars, you would still be advised NOT to look directly at that part of the sky when the impact happens. And folks on Earth will have a new companion star to the Sun, shining just as bright as the Sun, for the next couple of days before it begins to dim and fade slowly.

It was physicist Michio Kaku (author of Parallel Worlds), I think who said that even a tiny grain of interstellar dust striking a spacecraft moving near the speed of light would release energy equivalent of a thermonuclear warhead.

Linked below is a nice little story that depicts very accurately just what a solid (non-explosive) warhead can do if it strikes a planet moving at very close to the speed of light. The laws of physics and thermodynamics are observed very closely in this writing:
https://www.creepypasta.com/the-gift-of-mercy/

Last edited by Rachen; November 22, 2018 at 11:40 PM.
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Old November 23, 2018, 10:59 PM   #15
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You need to switch to a light gas gun to reach extreme velocities. You compress hydrogen or helium using an explosive charge driven cylinder, and use a burst disk to release a lot of compressed low viscosity gas into a small diameter barrel https://en.wikipedia.org/wiki/Light-gas_gun.
The highest "conventional bullet" velocities were probably achieved over a hundred years ago with the German Paris gun.
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Old November 24, 2018, 08:30 AM   #16
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Look at the " published " velocities for the 120mm smoothbore cannon in an M1 Abrahms tank. Keep in mind those are published...
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Old November 24, 2018, 09:37 AM   #17
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Per Tango19’s note and Wikipedia sourced:

Weight
1,190 kg (2,620 lb) Gun barrel
3,317 kg (7,313 lb) Gun mount
Length
L/44: 5.28 m (17.3 ft)
L/55: 6.6 m (22 ft)
Barrel length
44–55 calibers
Caliber
120 mm

Muzzle velocity
1,580 to 1,750 m/s (5,200 to 5,700 ft/s)


Effective firing range
4,000 meters (4,400 yd) with DM63[1]
8,000 meters (8,700 yd) with LAHAT[2]
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