interesting things i learned

[Brian Pfleuger]

Brian, how can you explain a complete understanding of the physics involved, which prove how the atmosphere, or more precisely the difference in the atmospheres, would effect velocity and then say that because the difference is minute that there is no effect at all?

I don't claim a "complete understanding". It's extremely complex in terms of getting a precisely correct, exact answer. However, the basic assumptions are not that complex.

Look at the differences in behavior between water and air. How extreme is it? In the grand scheme, it's not very extreme. You're talking about a density change of 800 times. Now think about the effect of taking away just 0.5gr of air and 14 psi in front of 50 or 60,000psi. What effect is that going to have?

Nearly none.

Think about it like this. Look at the effect of adding 400gr of mass in front of that bullet (air versus water) and then think of the effect of subtracting 0.5gr. How much difference is it going to make?
Venus? I don't know. The density is much lower than water but about 55 times higher than earths. The pressure is so high that it's technically a "super critical fluid" though.

[ATW525]

What would be the difference in firing a rifle on Venus as opposed to the earth?

50 miles above the surface of Venus I'd think it would be roughly the same, but a rifle is unlikely to even survive, let alone be functional, on the surface itself.

[DaleA]

Whew! It's been so long since we had a 'guns in space' thread I was starting to get worried.

I can't go into any of the details but I am smug that NOTHING brought up in this thread has made me redesign ANYTHING in my plans for the Lunar Trap and Skeet facility. (Which is a good thing because the Lunar Bowling Alley I designed had SIGNIFICANT problems which I won't go into now.

Venus...isn't the surface temperature about enough to melt lead? You might actually have a problem leaving a Glock in a closed car in the glove box out in the sun on a hot summer Venusian day...course maybe the cloud cover would help out.

[gyvel]

No, because recoil is a function of momentum, which does not change on the moon. It's related to mass, not weight. It'd be a problem out in space, where you have nothing to brace yourself against to stop the spinning but as long as your feet are on the ground it shouldn't matter.

So, reduced gravity wouldn't affect the effects of recoil, assuming this theoretical gun was fired from the shoulder?

[Doogle]

They fired it on a sound stage in California, (or maybe Elstree studios).

Everyone and their friends who work at NASA knows that!

[colbad]

I googled this and there actually is some interesting science behind it. Never thought you could fire w/o O2 but apparently its possible????? Makes me feel better that we can engage potential invading Aliens with a galactic expeditionary force...... or does this administration just give them amnesty and eventual citizenship??

[Brian Pfleuger]

Originally Posted by gyvel

So, reduced gravity wouldn't affect the effects of recoil, assuming this theoretical gun was fired from the shoulder?

It really shouldn't make any significant difference. All the relevant formulas are based on mass, not weight. The mass of both gun and shooter are constant, completely unaffected by gravity.

Of course, trying to shoulder a rifle while in a space suit would be interesting. Besides that the glove finger is probably bigger than the whole trigger guard.

Ignoring those real world concerns though, and just figure you could dress like you do on earth, the differences would be minor. Gravity probably helps some with getting the gun back in line after whatever vertical component of recoil there might be, so that might be noticeable. But as long as your feet are on the ground, it's friction that holds you there. That friction is influenced by gravity but it's not as if there's zero on the moon or you're on the ragged edge of going flying away even on earth.

Anyway, I wouldn't say there'd be no noticeable differences at all but it's not as if you'd go tumbling away like you got hit by a car.

[Mike Irwin]

"Never thought you could fire w/o O2 but apparently its possible?????"

Yes. Chemistry isn't my strong suite, but I think I have all of this GENERALLY correct...

Gunpowder, including black powder and modern smokeless powders, burn too quickly to be able to pull in adequate atmospheric oxygen, especially in the enclosed spaces in a gun.

Gunpowders contain chemical compounds called oxidizers, which supply all of the oxygen the gun powder needs as it combusts.

In black powder, the oxidizer is generally potassium nitrate (KNO3) or sometimes sodium nitrate (NANO3).

Modern smokeless powders get their reaction oxygen from a variety of chemicals based on the formula.

Single base powders are based on nitrocellulose (C6H9(NO2)O5).

Double base powders contain nitrocellulose and nitroglycerine (C3H5N3O9), which also provides oxygen to the reaction.

I believe that other chemicals are also part of the equation, onces that also add free oxygen, but I'm not 100% sure about that.

But, no matter what the formulation, there's enough oxygen generated during the reaction process to sustain it even if it's happening in a vacuum.

[Paul B.]

What would be the difference in firing a rifle on Venus as opposed to the earth?
Well, Venus is way too hot. If the gun itself didn't melt the cartridge would probably cook off. On the moon, who knows what the velocity would be? It's so cold even the least temperature sensetive powder would be seriously affected. I believe that even if you kept the gun in a heated container prior to firing the extreme cold would/could drop the powder temp enough to seriously affect it. You'd most likely need an extremely hot custom primer. Just my probaly unlikely WAG on the question.
Paul B.

[TailGator]

Gravity probably helps some with getting the gun back in line after whatever vertical component of recoil there might be, so that might be noticeable. But as long as your feet are on the ground, it's friction that holds you there. That friction is influenced by gravity but it's not as if there's zero on the moon or you're on the ragged edge of going flying away even on earth.

Mind you, it has been decades since I was in a physics classroom, but I think this might be oversimplifying the recoil problem in two respects.

First, there is a higher coefficient of friction when two surfaces are in contact with each other than when the same two surfaces are moving. The lower gravity on the moon (do I remember a figure of 1/6th correctly?) would decrease the force with which the two surfaces contact each other, and you would move from stationary friction to moving friction with less lateral force applied.

Secondly, it seems to me that the force would not be laterally applied, because it would be applied above the center of gravity of the shooter and impart a rotational motion to the shooter's body. The lift thus generated to the feet would be subject to the lower gravitational resistance of the moon.

I am sure my terminology is wrong, but hopefully I communicated my ideas cogently.

[Brian Pfleuger]

The principles you mention are more or less correct, the issue is with the magnitude of the forces.

There simply is not enough force to make anything happen.

Take a fairly high recoil rifle, .30-06, .308, etc, load it with one round. Jump up in the air as high as you can (keeping the gun pointed in a safe direction of course) and pull the trigger.

You now have NOTHING impeding your recoil induced motion until you hit the ground again. If anyone does this, I would love to know how much trouble you (don't) have with landing on your back/head/etc.

There's simply not that much force here. I'm not going to do the math again, but as I recall (I have done it before), a fairly powerful rifle will cause a 180 pound man to slide on a frictionless surface at a rate somewhere near 0.1fps. Someone else can figure it out if they want.

This is very much like the popular "knockdown power" discussions. There simply isn't enough power there, moon or earth.

[wogpotter]

I do have one thought on the effect of recoil on the shooter.

Even a golf club swing unbalanced an astronaut, I wonder if the different gravity would cause reflexes to mis-time & flip a shooter off balance in a lunar 1/6th gravity?

[HungryHunter]

I don't have much else to contribute so I'll take one for the team, and try Brian's experiment. Godspeed everyone.

[gothcopter]

A 55gr projectile traveling at 160,000fps has about 4.2MJ of energy -- the same as detonating a kilogram of TNT. That's one hell of a bang!

[TailGator]

There simply is not enough force to make anything happen.

I was picturing the slow-motion high and long strides of the Apollo astronauts when I wrote my argument, and imagining firing a gun in that environment. Your argument is quite persuasive though, and I think you might be right.

At least I don't have to say that to my wife.

[Mike Irwin]

"Even a golf club swing unbalanced an astronaut,"

What unbalanced Alan Shepherd was more the bulkiness of the space suit making it impossible for him to get a proper golfing stance.

Just found a discussion about the golf shot, and if Shepherd could have hit it just right, the ball could have traveled as far as 2.5 miles over 70 seconds.

In reality, though, neither one traveled anywhere near that far.

[DaleA]

if Shepherd could have hit it just right, the ball could have traveled as far as 2.5 miles over 70 seconds. In reality, though, neither one traveled anywhere near that far.

Looking at the videos again, I'm pretty sure he lifted his head.

[wogpotter]

Maybe, but he'd be wearing the same (or a similar suit) to do anything else on the moon. Maybe not with plaid pants, but you get the idea!

The point was more about being unexpectedly having to react to input in an unfamiliar environment. Weight differs, mass & inertia stay coupled so the instinctive reaction would be a false, but instinctive correction, even if there wasn't enough "raw power" to knock him down.

[Mike Irwin]

"Maybe, but he'd be wearing the same (or a similar suit) to do anything else on the moon. Maybe not with plaid pants, but you get the idea!"

Very true, but there's one critical difference between firing a gun and swinging a golf club...

Swinging a golf club requires CONTINUOUS movement and rebalancing of almost your entire body, something that's made far harder by the bulk of the suit.

In firing a rifle, you can bring it to your shoulder, take as long as you want to set your feet and get your grip, and from there the only thing you should move is your index finger.

Huge difference.

[captneil19]

ok guys you can call me down,i can't dispute what you say.You are talking way over my head,i was just passing along so of my conversation with him.I'm going to tell him he better go back to math school because my other friends say you ain't hitting on diddly.That rail gun must be really something ,I would like to see something like that in action.

[Mike Irwin]

There are videos of railguns in action on the net.

This is probably one of the better ones, but it's more a marketing piece...

https://www.youtube.com/watch?v=Fnm-etchLOk

There is some REALLY wild footage in it.

[Husqvarna]

did the us astronauts carry guns on the moon-mission? they were all military/airforce personel right?

atleast the russians did iirc... more to use if they crashlanded in siberia from what I have read

and why on earth (pun intended) did they play golf and not baseball?

[44 AMP]

So, without going into formulas, what can we safely assume?

You can fire a gun in space. (I don't know why some think it needs oxygen, it fires under water, too, doesn't it?)

The recoil energy is going to be the same.

The velocity might be different by a measurable, but not a practical amount.

in moon gravity, trajectory will be different. Also, at 1/6 the weight, your body's instinctive reactions (balance etc) will be affected.

Mercury, on the sun side is hot enough to melt lead. By comparison, Venus is much cooler. But only by comparison. Also the atmosphere of Venus is highly corrosive. That might be your biggest problem.

I recall one of the old sci-fi stories (written decades before the moon landing). Seems both sides (east & west) had bases on the moon. And of course, there was a war.

A short war, essentially one exchange of fire. The main character goes to the moon afterwards, and in the dome, he is being told about what happened. Until an alarm goes off and everyone hits the floor. A few bullets hit the dome, and then its over, until an hr or so later when the alarm goes off again...

Seems that while the shooting stopped a long time before, orbiting bullets from both sides were a regular danger.

Maybe that's not really possible, but it made a nice story.

[Mike Irwin]

No, US astronaut kit didn't include firearms. US returns were always water landings.

The Soviet returns were always over land, some of it rugged and quite remote. Including a rifle would be more logical for them.


"Also the atmosphere of Venus is highly corrosive. That might be your biggest problem."

That could likely be dealt by proper selection of alloys.

Don't for a moment, though, think that Venus is "cool."

Surface temperatures approach 900 deg. F, or more than enough to melt lead, and hotter than Mercury.

Surface atmospheric pressure is roughly 1,350 PSI, roughly equal to 900 feet below the surface of the sea on earth.

The combination of temperature and pressure are why probes dropped into the Venusian atmosphere generally crap out after only a few hours.