Sciencemadness Discussion Board

Understanding firearms "gun powder" vs explosives & their VOD's

RogueRose - 8-6-2020 at 02:10

I'm doing research on firearms and the powders that are used and I'm really shocked to learn the VOD of the various powders such as single, double and triple base powders with VOD of 7,300 - 8,200 m/s. This really blows my mind as I thought everything used in a firearm were not explosives, and that they just "burn" although very quickly - they deflagrate, which is burning (or expansion of gases) below the rate of sound. I thought the only reason the bullet reaches the speed it does is because of the compression of the gases, but looking at these VOD's, I'm thinking it might be from the actual explosion of the powder.

Do these powders not reach this VOD because they aren't compressed and do they reach that velocity if they are compressed and very tightly contained/packed? I know black powder acts this way, so I'm expecting these newer powders will do the same, but I'm still not sure how they are acting within the brass and chamber of the rifle.

What I'm wondering is if there is a limit to the speed that can be reached of the projectile using these powders, IF the chamber and barrel can be made of sufficient strength to contain the explosion. I'm looking at railguns and I don't think they reach the VOD of these powders, but if a barrel could be made that could contain the explosion, could the projectile reach the speed of the explosion, or even somewhat below (say 4-5,000 m/s)? It would seem that chemical propulsion would be a much more efficient &/or convenient means to fire projectiles than the pursuit of the railguns that seem to have kind of stalled in the last 10 years (unless there are a lot of unreleased advancements in energy storage).

We have been making gun barrels to withstand very high pressures since WWII with light gas guns and 2 stage guns. They seem to reach speeds of, or around railguns but in WWII there were limitations of materials and since then there have been HUGE advances in alloys capable of withstanding much higher pressures and temperatures, especially if talking about larger bores (not small arms). Metals & alloys like titanium and titanium/silicon carbide ceramic linings which have unbelievably high heat resistant temps and are incredibly wear resistant. Manufacturing large bore guns of this size, I would think, would be much easier than overcoming all the hurdles of railguns while having the same potentials and actually less expensive and more desirable (aerodynamically) ammunition/projectiles.

Sorry for the two part question, but the two topics kind of merged when I noticed the VOD of the powders that we use.

[Edited on 6-8-2020 by RogueRose]

[Edited on 6-8-2020 by RogueRose]

Dornier 335A - 8-6-2020 at 03:44

Gunpowders used as propellants burn (deflagrate) like black powder. Black powder can only deflagrate because the fuel and oxidizer is separated physically on the order of microns. Double base powders on the other hand have oxidizer and fuel in the same molecule so they can deflagrate if ignited by flame, or detonate if initiated by a strong shock. It shouldn't come as a surprise that these are powerful explosives seeing that it is basically the same thing as blasting gelatin. See this video for reference: https://www.youtube.com/watch?v=USg4d1WLQqE

The speed of a bullet is ultimately limited by the speed of sound in the expanding gases. This is true regardless of how the gas is produced. For gunpowders, that limit is about 2000 m/s even if you have an infinitely long barrel and an infinite amount of powder. Light gas guns achieve 9000+ m/s by increasing the speed of sound in the gas, not by increasing pressure.

So what happens if you use a blasting cap to initiate the powder instead? Would that increase the speed of the bullet? Yes, the bullet can be accelerated by the massive momentum of the shock wave instead of the relatively slowly expanding gases. We can approximate this case using Gurney equations (infinitely tamped sandwich, infinite propellant-to-bullet-ratio) to about 4500 m/s. The reason you don't see this used in cannons is that the pressure of the detonation is 20-30 GPa, which is higher than the yield strength of any material. The cannon would be single use. What I have described here is essentially an EFP.

Smokeless Powder

MadHatter - 9-6-2020 at 09:21

RogueRose, the triple-base powders have nitroguanidine
in them to suppress muzzle flash from artillery particularly
at night. The powder does indeed burn although very
rapidly. If there isn't enough barrel for the load unburned
powder can be thrown back in your face. This happened to
me firing a snub 357. MAG using a hot load. If the powder
explodes you're generally in trouble. A friend had a factory
.220 Swift cartridge explode destroying the gun and injuring
him. We still haven't figured out the cause although there
were no obstructions(sometimes a culprit) in the barrel.

SWIM - 9-6-2020 at 12:58

There are projectiles that use detonation to propel them, but not in a gun barrel.

Flexible plates of steel can be accelerated to some very high velocities by high explosives.
They're distorted into a totally different shape by the explosion.

There were munitions based on this principle, but I think they've gone out of style.

Looks like they call them explosively formed projectiles by what I see on a quick google search.

I thought they were named for a couple of 19th century munitions guys from Europe with the initials M and S, but I can't recall the actual names.

I believe one or more diacritical marks were involved, but don't hold me to it.



Pyro_cat - 26-6-2020 at 09:36


Do some searches on the space gun, efforts to put objects into orbit with cannons.

Been a wile since I looked at any of it but The escape velocity from Earth's surface is about 11,186 m/s (6.951 mi/s; 40,270 km/h; 36,700 ft/s; 25,020 mph; 21,744 kn) https://en.wikipedia.org/wiki/Escape_velocity

Very interesting psychics stuff.


The mad experiment
In a 500 feet long and 4 feet wide vertical cylindrical tunnel, they put a nuclear bomb. The top of this tunnel was sealed using a 4 inch thick man hole cover (on steroids). The lid weighed about 2 tons! They were sure that even the 2 ton lid would blow off like feather due to the nuclear explosion. However, they weren’t sure on exactly how fast it’d travel up. To measure the speed, high-speed cameras were placed near the opening.

The bomb was detonated. Some say that the high speed cameras were only able to capture the image of the lid in a single frame. Which by the way could also contribute to an enormous error margin in the speed calculation. Nevertheless, the speed was of the lid at which it flew up in the air was calculated to be 41 miles per second – approximately 6 times the escape velocity! More https://awesci.com/tag/fastest/

Edit, attempt top post a pic failed and I am to lazy to keep trying.



[Edited on 26-6-2020 by Pyro_cat]

RogueRose - 26-6-2020 at 12:44

Quote: Originally posted by Pyro_cat  

Do some searches on the space gun, efforts to put objects into orbit with cannons.

Been a wile since I looked at any of it but The escape velocity from Earth's surface is about 11,186 m/s (6.951 mi/s; 40,270 km/h; 36,700 ft/s; 25,020 mph; 21,744 kn) https://en.wikipedia.org/wiki/Escape_velocity

Very interesting psychics stuff.


The mad experiment
In a 500 feet long and 4 feet wide vertical cylindrical tunnel, they put a nuclear bomb. The top of this tunnel was sealed using a 4 inch thick man hole cover (on steroids). The lid weighed about 2 tons! They were sure that even the 2 ton lid would blow off like feather due to the nuclear explosion. However, they weren’t sure on exactly how fast it’d travel up. To measure the speed, high-speed cameras were placed near the opening.

The bomb was detonated. Some say that the high speed cameras were only able to capture the image of the lid in a single frame. Which by the way could also contribute to an enormous error margin in the speed calculation. Nevertheless, the speed was of the lid at which it flew up in the air was calculated to be 41 miles per second – approximately 6 times the escape velocity! More https://awesci.com/tag/fastest/

Edit, attempt top post a pic failed and I am to lazy to keep trying.



[Edited on 26-6-2020 by Pyro_cat]


Wow, that is an amazing story! I'm guessing that the lid atomized and that is why it couldn't be seen after the first frame. If it did indeed reach 41 miles per second in that short of time, the pressure of compression would have reached the BP of the metal within a fraction of a second. You would basically have all the energy of the bomb being focused into that one area. If you think of a shaped charge, which liquefies the metal b/c of pressure/heat/velocity, then I would think with so much more energy of a nuclear bomb that it would do more than liquify the metal (well briefly), it would vaporize it.

I also remember seeing some ideas for a space gun that was a circular track that would slowly accelerate in a circle until it got to speed where a door/gate would open and it would go out of the loop and be turned up a long "barrel" and accelerated through the exit. I would think this could work using magnetic propulsion especially if a vacuum could be pulled in the track and whatever being launched be levitated in the track. I'm guessing it might even be possible for humans if you would make the vehicle rotate to keep G forces consistent, or at least not sudden changes. It's an interesting idea to ponder.

[Edited on 6-26-2020 by RogueRose]