How well would a firearm like the M4 perform in outer space?

[The Annoyed Man]

This discussion has officially passed the threshold of conversations that I can meaningfully participate in on my phone during quick breaks at work, so I'll limit my response to the following for right now:

I don't think the M4 would be classified as a black body.

Great discussion. Let's talk about some more physics

Dude, I was a physics major. EVERYTHING (stars, trains, horses, M4s, etc.) is a spherical blackbody in a frictionless vacuum. And all constants are some power of ten multiplied by "about 3".

The "spherical cow" approach is close enough for government work, and certainly close enough for Internet spitballing about guns in space.

Good Lord! Sheldon Cooper has gone and gotten himself a CHL!

Q: How many theoretical physicists specializing in general relativity does it take to change a light bulb?
A: Two. One to hold the bulb and one to rotate the universe.

Q: What is the simplest way to observe the optical Doppler effect?
A: Go out at and look at cars. The lights of the ones approaching you are white, while the lights of the ones moving away from you are red.

The Heineken Uncertainty Principle says "You can never be sure how many beers you had last night."

According to Einstein's Theory of Relatives, the probability of in-laws visiting you is directly proportional to how much you feel like being left alone.

Einstein's favorite limerick was:
There was an old lady called Wright
who could travel much faster than light.
She departed one day
in a relative way
and returned on the previous night.

A student riding in a train looks up and sees Einstein sitting next to him. Excited he asks, "Excuse me, professor. Does Boston stop at this train?"

There is a sign in Munich that says, "Heisenberg might have slept here."

I'll be here all week. Don't forget to tip your waiter.

[Dadtodabone]

I'll go with Penny, I love Fig Newtons.
[youtube][/youtube]

[The Annoyed Man]

I'll go with Penny, I love Fig Newtons.

I'll go with Penny for almost any reason whatsoever.

[jimlongley]

Believe it or not, in my own true Sheldon Cooper style, I was ruminating on this issue while undergoing acupuncture treatment this afternoon, and realized that using a full auto M4, with adequate heat dispersal, might serve well as a propulsion system, ala "nuclear pulse propulsion."

Let's see F=ma, assume that m = ~250Kg, F = (Free recoil energy of the gun (say an average .223 with 55 grain projectile; 27 grains of powder; 3240 fps muzzle velocity; 7 lb (actually included in the initial mass estimate);1.27 lb/sec recoil impulse; 5.8 fps recoil velocity; 3.7 lb recoil energy)) then a would be F divided by m. F, normalized for differences in units

This, it might take a lot of rounds, but one might expect about .03 m/sec per shot acceleration, so after about 100 rounds, one could accomplish a velocity of 1 m/sec, or a fast walk.

I think.

But now my head hurts.

I must go view back episodes of Big Bang Theory until I have an adequate Penny fix.

[Steve133]

This discussion has officially passed the threshold of conversations that I can meaningfully participate in on my phone during quick breaks at work, so I'll limit my response to the following for right now:

I don't think the M4 would be classified as a black body.

Great discussion. Let's talk about some more physics

Dude, I was a physics major. EVERYTHING (stars, trains, horses, M4s, etc.) is a spherical blackbody in a frictionless vacuum. And all constants are some power of ten multiplied by "about 3".

The "spherical cow" approach is close enough for government work, and certainly close enough for Internet spitballing about guns in space.

It's a good thing I didn't state unequivocably that the object would not be a black body. A simple as I recall statement would have sufficed rather than condescension.

But that's just the way I approach things.

Apologies, still not sure how that statement was taken as being condescending, but that certainly wasn't my intent. I was going for "yeah, it's not exact, but I'm just a dumb physicist, I can't do exact" comment - self deprecating jokes about only being able to think about spherical frictionless cows are pretty common in physics circles (abstraction to the point of uselessness is part of why I'm now an engineer instead of a physicist), but I guess that doesn't come across as well in text as it does in speech.

That said, this IS about the first time that a topic that I'm this uniquely qualified to talk about has come up on this board, can't promise I won't get carried away again....

[JSThane]

Believe it or not, in my own true Sheldon Cooper style, I was ruminating on this issue while undergoing acupuncture treatment this afternoon, and realized that using a full auto M4, with adequate heat dispersal, might serve well as a propulsion system, ala "nuclear pulse propulsion."

Now I'm remembering the concept of the Orion Drive...

[Dadtodabone]

I'll go with Penny, I love Fig Newtons.

I'll go with Penny for almost any reason whatsoever.

As an aside, I think I met Sheldon's mother at The Egg & I, after church last Sunday. Not Jim Parson's mother, I mean Sheldon's mother, as played by
Ms. Metcalf. I always thought she was a caricature, lol.

[Purplehood]

Isn't the Orion-drive simply a massive nuclear-version of what one might be able to accomplish in space with severe-flatulence?

[jimlongley]

I'll go with Penny, I love Fig Newtons.

I'll go with Penny for almost any reason whatsoever.

As an aside, I think I met Sheldon's mother at The Egg & I, after church last Sunday. Not Jim Parson's mother, I mean Sheldon's mother, as played by
Ms. Metcalf. I always thought she was a caricature, lol.

I have met several caricatures, and it never ceases to be a surprise. I always find myself wondering if they pattern themselves after the prototype, or they are just that way naturally. The whole story is way too long, but my late wife used to have a student who laughed just like Horshack (sp?) in "Welcome Back Cotter" and the whole class would break up in helpless laughter whenever she laughed. We often wondered if she knew they were laughing at her/the laugh, instead of with her.

[jimlongley]

Believe it or not, in my own true Sheldon Cooper style, I was ruminating on this issue while undergoing acupuncture treatment this afternoon, and realized that using a full auto M4, with adequate heat dispersal, might serve well as a propulsion system, ala "nuclear pulse propulsion."

Let's see F=ma, assume that m = ~250Kg, F = (Free recoil energy of the gun (say an average .223 with 55 grain projectile; 27 grains of powder; 3240 fps muzzle velocity; 7 lb (actually included in the initial mass estimate);1.27 lb/sec recoil impulse; 5.8 fps recoil velocity; 3.7 lb recoil energy)) then a would be F divided by m. F, normalized for differences in units

This, it might take a lot of rounds, but one might expect about .03 m/sec per shot acceleration, so after about 100 rounds, one could accomplish a velocity of 1 m/sec, or a fast walk.

I think.

But now my head hurts.

I must go view back episodes of Big Bang Theory until I have an adequate Penny fix.

Are you confusing mass and weight, Jim?

Not unless I have made a massive error.

[Dave2]

Are you confusing mass and weight, Jim?

Not unless I have made a massive error.

Really? Puns at a time like this? You fail to understand the gravity of the situation.

[WildBill]

I have worked on space hardware used on shuttle and ISS EVAs and well as rocket propulsion systems.

As I recall, Braycote was the most common lubricant on the EVA hardware. Many items also had surface coating as lubricants. Many of the EVA tools are commerically available items that have been modified for some of the conditions of space as well as crew safety. For example, torque wrenches that you could buy at Sears and Black and Decker battery-powered drills and screwdrivers. We did vibration and temperture cycle testing as part of the design verification and acceptance testing.

A caveat - if exposed to very low temperatures [-200F] carbon steel and brass will crack, so a kaboom is likely.

I have no doubt that the cartridge would fire and the gun would cycle. Many people are still confused by "gunpowder" containing "oxygen". That is true with black powder, but not smokeless powder. Smokeless powder is actually a propellant that works by decomposing into gasses. The heat expands the gasses and propels the bullet from the barrel.

[WildBill]

I have no doubt that the cartridge would fire and the gun would cycle. Many people are still confused by "gunpowder" containing "oxygen". That is true with black powder, but not smokeless powder. Smokeless powder is actually a propellant that works by decomposing into gasses. The heat expands the gasses and propels the bullet from the barrel.

I did not know that.

Nitroglycerin, a component of double-based powder, is a perfect example. It is a pure chemical containing oxygen and nitrogen. When it decomposes it creates nitrogen gas and heat. The heat expands the nitrogen gas and that is what causes the increase in pressure that causes the bullet to travel down the barrel. Of course, pure nitroglycerin would decompose so fast that it would destroy the gun.

When I was in the solid rocket motor business one test that we performed measured the burn rate of the propellant by burning it under water. That type of propellant did have an oxidizer mixed into the formulation.