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November 21, 2018, 04:25 PM | #1 |
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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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November 21, 2018, 05:40 PM | #2 | |
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I found this online:
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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. |
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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November 22, 2018, 02:49 AM | #5 | ||||||
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November 22, 2018, 06:17 AM | #6 |
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Velocity is limited by friction in the barrel and cannot equal the pressure wave propagation.
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November 22, 2018, 08:44 AM | #7 |
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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. |
November 22, 2018, 09:47 AM | #8 | |
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November 22, 2018, 01:33 PM | #9 | |
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November 22, 2018, 04:29 PM | #10 | |
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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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November 22, 2018, 06:10 PM | #11 | |
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Theoretical considers known factors. “Ideal” is eliminating factors by setting the environment in outer space, for example.
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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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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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November 22, 2018, 10:21 PM | #14 | |||
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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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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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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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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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