Low Gravity and Recoil

[sarduy]

What would me the difference in recoil between, say, firing a 12ga shotgun in the earth's surface vs firing the same shotgun on the surface of the moon? Would felt recoil (ignoring the obvious issue of spacesuits providing a recoil buffer ) be the same, or more?

Random question, I know, but I am a curious fellow with only a passing understanding of physics. Thanks in advance

A: you landing 20-50 feet away from where you were standing due to less gravity.

If you weight 200lb on earth, you weight about 33.2lb on the moon. Your weight on the moon is a function of the moon's gravity. First, we know that gravity is a force that attracts all physical objects towards each other (but why this happens is largely unknown!). Second, the greater the mass of an object, the stronger the force of gravity.

The moon is 1/4 the size of Earth, so the moon's gravity is much less than the earth's gravity, 83.3% (or 5/6) less to be exact. Finally, "weight" is a measure of the gravitational pull between two objects. So of course you would weigh much less on the moon. Imagine how far you could jump on the moon! The Apollo astronauts apparently had fun

ETA: same goes for the ammo, if you shoot a slug it will go about 83% further

 

[Jim Watson]

One correction. Smokeless gunpowder does not "contain its own oxidizer." (Black does.)
The nitrocellulose and nitroglycerine in a double base powder are specific chemical compounds that are unstable. Poke it with a primer and they decompose into hot gas.

 

[Kliegl]

No, Mist, he just doesn't get it. I gave up.

 

[HOOfan_1]

No, Mist, he just doesn't get it. I gave up.

I do get it...I got it from the beginning. The difference in pressure between the chamber and the outside on the moon versus the difference in pressure between the chamber and the outside at sea level on earth is so infinitesimal that it is negligible to felt recoil.

 

[Kliegl]

Ok, cause, dude, you just contradicted yourself.

 

[MistWolf]

One correction. Smokeless gunpowder does not "contain its own oxidizer." (Black does.)
The nitrocellulose and nitroglycerine in a double base powder are specific chemical compounds that are unstable. Poke it with a primer and they decompose into hot gas.

Smokeless powder contains it's own catalyist

 

[Jim Watson]

Catalyst?
It contains what you might call an anti-catalyst in the stabilizer and coating package. Nitrocellulose sure doesn't need a catalyst, the thing that had to be learned was how to tone it down to where it could be used as a propellant instead of just an explosive.

 

[1911Tuner]

A: you landing 20-50 feet away from where you were standing due to less gravity.

If you weight 200lb on earth, you weight about 33.2lb on the moon. Your weight on the moon is a function of the moon's gravity.

Gravity has nothing to do with it. Mass is constant, regardless of the gravity and atmosphere, or lack of same. If X force is used to accelerate the system...then the force will be X even in a weightless environment. If there is any difference in velocity...bullet or gun...it will be so small that it can be ignored.

Think about it this way:

In the weightlessness of space, a baseball and the Washington Monument weigh exactly the same. Nothing. You can throw the baseball easily, but you can't move the monument...even if your foot is braced against the space shuttle. Its mass is too great.

If you're standing on the moon, firing a .308 rifle with exactly the same braced stance that you would normally take on Earth...your body movement will be exactly the same because...mass is constant.

 

[kozak6]

A shotgun is an interesting choice for the surface of the moon. Without a significant atmosphere, there is no impetus for the shot to scatter.

If you are going to be doing much shooting (and you will be, if it's the new Moon map for Black Ops), heat build up might also be a problem since there is no atmosphere to cool the gun.

 

[Kliegl]

Whoa!

Do you know how COLD space is? It's the total absence of anything. Think absolute zero.

However, the sun is unmitigated, so stuff in its view gets really hot.

 

[Sam Cade]

Do you know how COLD space is? It's the total absence of anything. Think absolute zero.

No atmosphere to cool the weapon though so it has to dump all of its heat via radiation.

Figure around 250 Deg Fahrenheit for a weapon in sunlight plus the heat generated by firing......

 

[Kliegl]

No kidding.

I see I need to do an impromptu Heat Transfer course. Ahem, cough, Ahem.

STUDENTS, HEAR ME!!!!

There are 3 kinds of Heat Transfer:
1. Conduction.
2. Convection.
3. Radiation.

Conduction is transfer through surface contact. If you have ever picked up a hot pot,
or a cold beer, you have experienced conduction.

Convection is through a medium coming by the object and absorbing or giving heat, depending on the direction of the gradient. If you have ever stood under a fan, you have experienced convection.

Radiation, in addition to being isotope decay, is when a object simply sheds heat into the immediate area. If you have ever stood in the sunlight on a still day, you have experienced radiation.

Also, heat transfer is related to the difference between the two temperature wells. If you have ever stepped outside without a coat in the winter, as opposed to the spring, you know the difference.

Applying the above gets you the following:
A: A gun cannot cool in outer space by convection.
B: Space is so damn cold that radiation heat transfer will more than suffice.

This has been Professor Kliegl, with the University of Farmers.

 

[Kliegl]

Ah boo, Cade, you redid your post while I was typing. Fail.

 

[Sam Cade]

Ah boo, Cade, you redid your post while I was typing. Fail.

Did not, no edit.

 

[Burt Blade]

Lunar/space conditions are not healthy for current fireams.

In a near vacuum, all the oil will boil away, leaving any dissolved solids. Dry metal can vacuum weld, which is not exactly a good thing for moving parts. (Not sure if the Moon's trace atmosphere is enough to prevent this.)

Temperatures vary from ~+250 to ~-290 on the Moon. This is outside the intended range for ammunition. Effects on performance will be severe. You go from one extreme to the other by stepping in and out of shadows. This is also not exactly good for the metal, wood, and/or plastic in the weapon.

Downrange performance will be quite different, assuming the above minor details have been addressed. Drag=zero, and drop due to gravity is much less on the Moon. I would expect max effective range to go up quite a bit. If you make the softpoint slug nose-heavy, you can omit the rifling for a significant velocity gain. If you do not care about expansion from a soft-point, the round can fly any-whichway and still fly straight. A chunk of brick is as accurate as a high-end match-grade VLD.

Shotgun spread will be limited to forces applied at the muzzle, from the choke, wad, and muzzle blast. Shot will carry just as far as anything else. No drag to slow it down.

Escape speed at the Lunar surface is ~2.4km/s, or roughly 7800 fps. A 3000+ fps rifle round is going to carry a very long way, with great accuracy. No wind drift. No spindrift. There would be a huge advantage to light and fast loads, as you no longer need greater mass to carry energy downrange to beat drag and wind. With the right setup, you could darn near put a man-fired round into orbit. Back-shot could take on new meaning. The 120mm smoothbore main gun of an M-1 tank, loaded with a lightweight rod, could hit orbiting targets. Or shoot rounds at the Earth.

Tranquility Firebase here….. On the way!

 

[Sam Cade]

B: Space is so damn cold that radiation heat transfer will more than suffice.

Betcha it won't.


Heat exchange via radiation is SLOW and local space isn't particularly cold. Sure if I tossed my foe out of an airlock he would eventually freeze, several hours later.

Remember how Laika the Space-Dog Died?
Her cooling system failed and her own body heat killed her..


Look at the size of the radiators on the ISS need to keep it cool enough to live in
http://microgravity.grc.nasa.gov/SpaceOps/ISS/Propulsion/ISS_comp.jpg

 

[Kliegl]

Space is cold, just not in sunlight.

And you did too edit that post, it just doesn't show the edit if you do it before the next post, heh.

The Moon is a Harsh Mistress, a book by the Grand Master, Heinlein, covers lunar escape velocity, they set up catapults to rock-bomb Earth till they got independence.

 

[Sam Cade]

The Moon is a Harsh Mistress, a book by the Grand Master, Heinlein, covers lunar escape velocity, they set up catapults to rock-bomb Earth till they got independence.

Virginia did all of his math for him.


Remember, Lazarus was based on Ginny.

 

[Kliegl]

I thought Maureen was.

 

[Sam Cade]

I thought Maureen was.

They both were. Maureen was Ginny, Lazarus was Ginny as she would have been as an immortal man.... and then you have the twin cross sex clones of Lazarus....who would be Ginny/Maureen....

Time Enough for Love got pretty confusing toward the end.

 

[Kliegl]

No kidding. If ever found a redheaded wife and got a daughter with the same out of it, Lorelei would work for a name, as I already got the Lee surname. While I enjoyed the time romping love fest later Heinlein novels, I preferred some of the non-hedonistic earlier ones like Starship Troopers, the Puppet Masters, and Glory Road more.

 

[aggieoutlaw]

This is a silly topic but I may as well indulge.

Space is not cold. Space is nothing. Temperature is a measure of the internal kinetic energy of matter. Without matter, there is no temperature...sorry. The lunar surface has matter and a very thin atmosphere, so convection and thermal radiation still apply.

Radiative heat transfer is very inefficient at low temperatures (which your gun is presumably at when removed from your inhabitable vehicle/shelter). See Stefan-Boltzman constant.

Newton's laws still apply. Momentum and energy are conserved. Gun fires and recoils just about the same...

 

[Flopsweat]

In the end it won't matter how cold it is because no one can hear you scream anyway.

 

[Kliegl]

That's some of that aggie engineering....think you missed something there, hoss.

 

[MistWolf]

Catalyst?
It contains what you might call an anti-catalyst in the stabilizer and coating package. Nitrocellulose sure doesn't need a catalyst, the thing that had to be learned was how to tone it down to where it could be used as a propellant instead of just an explosive.

Combustion requires a fuel and a catalyst