Fun with guns.. in space!

While most of the questions I get asked on a daily basis are “what’s going to happen in 2012?! (nothing, don’t listen to the History channel)” and “do you think aliens exist? (yes, both sentient and non-sentient)” I do occasionally get the question of what would happen if a gun was fired in space – and to make it interesting, I won’t just say a one sentence answer..First, let’s flatten out the playing field. Any bullet fired in this experiment is a 9mm bullet, fired from a normal, unmodified gun, and that bullet is 120 grain weight. What do you think would happen?

  • Would it continue on as normal, as if firing from Earth?
  • Would a click be heard, and nothing happen (no bullet fired)?
  • Would you go flying backwards, and the bullet not move?
  • Would the bullet or gun explode, possibly because of..


Well, the answer(s) are complex, but to make things simple, let’s assume that there is no defects in any of the weaponry or ammunition, and the person firing the weapon can survive in outer space without the need for protective equipment. Modern gun powder contains Potassium Nitrate, an oxidizing agent, and bullets no longer require oxygen to be present to spark (like old musket and black powder rifles from pre-1900’s). This is why some guns can be fired under water (how far that bullet will travel, if it travels anywhere at all, is another question). So we’ve already eliminated the “click, nothing happens” clause. The near negative pressure of space would’ve already had an effect on the bullets, and any sort of expanding and contracting, situational on what would actually happen to that bullet, would’ve already happened, so no, the bullet and gun wouldn’t explode (short of either having an actual defect). Now that the two easy answers are out of the way, let’s get to the more complex questions. Would the gun and person firing the gun fly backwards, leaving the bullet stationary in its original position. Many people believe this to be true, but those many people, are wrong. Assuming that there is no gravitational force pulling on either person, bullet or weapon, what would happen is exactly what you would expect to happen. The bullet would fire normally. Why would this happen? While there is no star nearby on this person pulling him/her towards it (Gravity), the body of the person itself is causing gravity on the gun and bullet. While it is so slight when compared to the Earth’s pull on humans, it is enough to correct the inertia on the bullet to make it fire normally, straight out the barrel. The shell casing would eject and fly off into space, and you would be floating there now with a small amount of thrust in the opposite direction of that bullet. This is Newton’s 3rd law of motion: For every action there is an equal and opposite reaction.

But wait, there’s more! Call now and get the 1st law of motion absolutely free! Just pay separate processing and handling..

That bullet you just fired, is now forever alone, destined to travel at the speed it was fired (~1km / second). That’s because Newton’s first law states that an object in motion will not change its velocity unless an unbalanced force acts upon it (Uniform motion). Until the bullet strikes an object in space, or a force such as gravity begins to effect it, that bullet will continue to travel in a straight line, not slowing down. Let’s assume that it will never encounter a secondary force such as gravity, and no object will ever cross paths. What would happen? In a few trillion years, would it eventually hit the edge of the universe? Not even close. That bullet is forever alone remember? The universe is expanding at a rate roughly calculated to be 20km/second, and that bullet is traveling at 1/20th that speed.

Let’s throw some spaghetti into the mix.. just for shits and gigs

You are now standing on the Moon, perfectly aligned with the equator (because you have a laser guided positioning implant). You hold the gun away from you, aimed perfectly along the equator at 45 degrees from the ground (perfectly aimed and angled because you also have a robotic arm). Keeping in mind that the Moon has 1/6th the gravity, what would happen? Say goodbye to your knees. In roughly 3 hours, that bullet will have traveled the entire circumference of the moon. The bullet we’re using in these equations has an average distance traveled of 2.3km, traveling at 1km per second, so it travels 2.3km in 2.3 seconds. The moon is 10,917km at the equator, so a simple division gives you the result that the bullet would travel 10917km in 10917 seconds, or 3.034 hours. There is no air on the moon, so pesky things like air resistance are not factored into this, and we’re standing on the equator so the Coriolis effect doesn’t come into play either. So, if you want to kill yourself, but don’t want to be suspected of suicide in post death, go to the moon, align yourself perfectly with the equator and fire a gun perfectly aimed, then throw the gun away as hard as you can. It’s pretty likely that the average person can throw a gun to escape the gravitational pull of the moon, so all they’ll see is a person who’s been shot and no gun found.

The first moon murder.

Jeff Wilton

Jeff is the founder and owner of Everyday Science Stuff. ESS is a one man operation, with the core belief that all education should be served without crippling debt tuition, without revenue generating ads and without any restrictions of any kind such as paywalls, forced login and account creations, geographical restrictions, and so on.

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