# Would a bullet travel faster on the moon? **URL:** \ **Category:** Factual Questions\ **Created:** [August 2, 2000, 1:10pm UTC](https://boards.straightdope.com/t/would-a-bullet-travel-faster-on-the-moon/27835 "2000-08-02T13:10:46Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![Guy\_Propski](https://avatars.discourse-cdn.com/v4/letter/g/5e9695/32.png) [@Guy\_Propski](https://boards.straightdope.com/u/Guy_Propski)\ **Post date:** [August 2, 2000, 3:54pm UTC](https://boards.straightdope.com/t/would-a-bullet-travel-faster-on-the-moon/27835/21 "2000-08-02T15:54:57Z")
Mr. Cynical–please see my earlier comment. I’m sure the gun afficianados on this page can provide more detail on this, too. The astronaut that drove a golf ball on the moon was Alan Shepherd, and it was on Apollo 14. He had to swing one-handed, due to the bulkiness of his space suit. Also, his club was just a 6-iron head on one of his tools. After whiffing the first two swings, he connected on the 3rd. He joked that it went “miles and miles”, but I think it was a lot shorter than 1/6 of a mile. Since they were at the end of their last EVA, they never got a chance to measure it. ---
**Author:** ![Sofa\_King](https://avatars.discourse-cdn.com/v4/letter/s/58956e/32.png) [@Sofa\_King](https://boards.straightdope.com/u/Sofa_King)\ **Post date:** [August 2, 2000, 4:08pm UTC](https://boards.straightdope.com/t/would-a-bullet-travel-faster-on-the-moon/27835/22 "2000-08-02T16:08:04Z")
Yes, a cartridge would work quite well without external oxygen. The powder supplies its own oxidizer. Just to anticipate the next question, the escape velocity of the moon is about 2.38 Km/s, or over twice the muzzle velocity of Joe\_Cool’s rifle. So you couldn’t shoot a normal rifle from the moon and hit the earth. However, since the moon has no atmosphere, the lowest stable orbit is a perfectly circular one that just misses the highest point on the moon’s surface. So if one were to get to the highest spot on the equator of the moon, face due east, and fire a rifle, you might be able to put that bullet into orbit. You also wouldn’t want to wait around too long before climbing down. Unfortunately, I’m not capable of calculating what a minimum orbital velocity around the moon would be. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [August 2, 2000, 4:36pm UTC](https://boards.straightdope.com/t/would-a-bullet-travel-faster-on-the-moon/27835/23 "2000-08-02T16:36:44Z")
Circular orbital speed is equal to 1/sqrt(2) times escape speed, so Joe\_Cool’s rifle couldn’t do it (unless the velocity increase due to vacuum were great enough) but it could come close, travelling a significant way around, and it probably wouldn’t be too hard to find a rifle that could do it. Do m16s et al. have higher muzzle velocities? If you’re on the highest mountain on the Moon (about a mile high, I believe), and there’s no other mountains in your way, you could make do with a little less than circular orbit speed, but not by any significant amount. ---
**Author:** ![Saltire](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/saltire/32/553_2.png) [@Saltire](https://boards.straightdope.com/u/Saltire)\ **Post date:** [August 2, 2000, 4:52pm UTC](https://boards.straightdope.com/t/would-a-bullet-travel-faster-on-the-moon/27835/24 "2000-08-02T16:52:19Z")
> [@](#): > > \*Originally posted by scr4 \* > \*\* > > > [@](#): > > > > \*Originally posted by Coldfire \* > > **A missile uses a propulsion system that NEEDS the friction of the Earth’s air.** > > This depends on the missile. This is definitely true for cruise missiles which use jet engines. Ballistic missiles and, I think, smaller missiles (e.g. air-to-air missiles) use solid fuel rockets, which work perfectly fine in vacuum. The nozzle shape is optimized for atmospheric use, so it would be less efficient, but you have no air to push through, so whether it actually goes faster or slower is hard to say. I’d guess most missiles would fly faster. \*\* They’d fly faster, but most of them would begin to tumble fairly early in the flight. Missiles designed for Earth use may not need air for propulsion, but most of them rely on air for all or part of their guidance. The fins make sure the whole thing stays straight. So, a Moon missile would have to have a more sophisticated system, using auxiliary jets to keep itself pointed where it needed to go, or maybe multiple controllable rocket nozzles in the base. ---
**Author:** ![Sofa\_King](https://avatars.discourse-cdn.com/v4/letter/s/58956e/32.png) [@Sofa\_King](https://boards.straightdope.com/u/Sofa_King)\ **Post date:** [August 2, 2000, 5:09pm UTC](https://boards.straightdope.com/t/would-a-bullet-travel-faster-on-the-moon/27835/25 "2000-08-02T17:09:43Z")
Many missles use internal inertial guidance systems. Whether they are strong enough to be used without the help of control surfaces is another matter. ---
**Author:** ![Joe\_Cool](https://avatars.discourse-cdn.com/v4/letter/j/ecb155/32.png) [@Joe\_Cool](https://boards.straightdope.com/u/Joe_Cool)\ **Post date:** [August 2, 2000, 5:13pm UTC](https://boards.straightdope.com/t/would-a-bullet-travel-faster-on-the-moon/27835/26 "2000-08-02T17:13:58Z")
> [@](#): > > \*Originally posted by Chronos \* > \*\*Circular orbital speed is equal to 1/sqrt(2) times escape speed, so Joe\_Cool’s rifle couldn’t do it (unless the velocity increase due to vacuum were great enough) but it could come close, travelling a significant way around, and it probably wouldn’t be too hard to find a rifle that could do it. Do m16s et al. have higher muzzle velocities? > If you’re on the highest mountain on the Moon (about a mile high, I believe), and there’s no other mountains in your way, you could make do with a little less than circular orbit speed, but not by any significant amount. \*\* Well my rifle is a Mini-14, which fires the same round as an M-16 (.223, or 5.56mm NATO). If you started with a faster round like a BAR .50, that plus the higher muzzle velocity due to vacuum, plus a ligher bullet, plus a really heavy powder charge and a longer barrel you _might_ be able to get close. I haven’t been able to find ballistics numbers on the .50 so far, though. Wouldn’t it make moon landings more interesting if there were a few anti-armor bullets orbiting at low altitude? haha ---
**Author:** ![Mr.Cynical](https://avatars.discourse-cdn.com/v4/letter/m/ee59a6/32.png) [@Mr.Cynical](https://boards.straightdope.com/u/Mr.Cynical)\ **Post date:** [August 2, 2000, 5:14pm UTC](https://boards.straightdope.com/t/would-a-bullet-travel-faster-on-the-moon/27835/27 "2000-08-02T17:14:50Z")
Thanks guys! I was stuck on that one pretty well. I wasn’t sure at all if the propellant contained it’s own oxidizer. My hat’s off to you! ---
**Author:** ![Diver](https://avatars.discourse-cdn.com/v4/letter/d/858c86/32.png) [@Diver](https://boards.straightdope.com/u/Diver)\ **Post date:** [August 2, 2000, 7:44pm UTC](https://boards.straightdope.com/t/would-a-bullet-travel-faster-on-the-moon/27835/28 "2000-08-02T19:44:04Z")
Coldfire said “Supersonic speeds? I don’t think so.” A sidenote Coldfire; if you are close enough so that it’s still supersonic, you can acually hear the sonic boom as a bullet passes by you. ---
**Author:** ![manhattan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/manhattan/32/7_2.png) [@manhattan](https://boards.straightdope.com/u/manhattan)\ **Post date:** [August 2, 2000, 10:34pm UTC](https://boards.straightdope.com/t/would-a-bullet-travel-faster-on-the-moon/27835/29 "2000-08-02T22:34:11Z")
Unless, of course, you are distracted by the fact that you just wet your pants because there are bullets flying by. 😉 ---
**Author:** ![Boris\_B](https://avatars.discourse-cdn.com/v4/letter/b/fbc32d/32.png) [@Boris\_B](https://boards.straightdope.com/u/Boris_B)\ **Post date:** [August 2, 2000, 10:50pm UTC](https://boards.straightdope.com/t/would-a-bullet-travel-faster-on-the-moon/27835/30 "2000-08-02T22:50:05Z")
I’m splitting hairs here, but a lot of common handgun cartridges are subsonic. .22 LR and .45 ACP, as have been mentioned, plus .25 ACP, .380 ACP, many .38 Special loads, and lots of the bigger revolver cartridges are subsonic. [http://www.winchester.com/products/index\_chgun.html](http://www.winchester.com/products/index_chgun.html) That link shows some popular handgun loads. Mach at sea-level is between 1000 and 1100 feet per second, if I remember correctly. Shotgun and rifle projectiles are almost always supersonic, though. ---
**Author:** ![Diver](https://avatars.discourse-cdn.com/v4/letter/d/858c86/32.png) [@Diver](https://boards.straightdope.com/u/Diver)\ **Post date:** [August 4, 2000, 7:28pm UTC](https://boards.straightdope.com/t/would-a-bullet-travel-faster-on-the-moon/27835/31 "2000-08-04T19:28:19Z")
Manhattan said “Unless, of course, you are distracted by the fact that you just wet your pants because there are bullets flying by” You can’t do that. Your peers would laugh at you - for the rest of your life, at least. All seriousness aside, I always found the adrenaline provided an intense focus rather than a distraction. ---
**Author:** ![Joe\_Cool](https://avatars.discourse-cdn.com/v4/letter/j/ecb155/32.png) [@Joe\_Cool](https://boards.straightdope.com/u/Joe_Cool)\ **Post date:** [August 4, 2000, 8:34pm UTC](https://boards.straightdope.com/t/would-a-bullet-travel-faster-on-the-moon/27835/32 "2000-08-04T20:34:08Z")
> [@](#): > > \*Originally posted by Boris B \* > \*\*I’m splitting hairs here, but a lot of common handgun cartridges are subsonic. .22 LR and .45 ACP, as have been mentioned, plus .25 ACP, .380 ACP, many .38 Special loads, and lots of the bigger revolver cartridges are subsonic. > [http://www.winchester.com/products/index\_chgun.html](http://www.winchester.com/products/index_chgun.html) > That link shows some popular handgun loads. Mach at sea-level is between 1000 and 1100 feet per second, if I remember correctly. > > Shotgun and rifle projectiles are almost always supersonic, though. \*\* .22LR is, in fact, a relatively fast round. Your link lists it at both 1250 and 1280 fps at muzzle, and about 1015 fps at 100 yards. Speed of sound is only 1088fps, making the .22 a supersonic round. Regarding the .22 short, .380 and .25 ACP, I ignored them because they are relatively useless rounds (I once shot a .25 at a piece of sheet rock, and not only did it NOT penetrate, it only made a dent about 3/16" deep and bounced off. Not that I want to be hit by one, but I’m not terribly afraid of it causing death). But as for subsonic rounds being very common, it seems I was mistaken. In handguns, they appear almost as common as supersonic, as you said. But it looks like Winchester considers anything over 1000fps to be supersonic, which is off by about 8%. ---
**Author:** ![KeithB](https://avatars.discourse-cdn.com/v4/letter/k/48db29/32.png) [@KeithB](https://boards.straightdope.com/u/KeithB)\ **Post date:** [August 4, 2000, 9:14pm UTC](https://boards.straightdope.com/t/would-a-bullet-travel-faster-on-the-moon/27835/33 "2000-08-04T21:14:17Z")
While not exactly OT, it is pertinent. I remember a cold war era SF story about an American and Russian Moon Base. Someone was sent to the moon to figure out why they were asking for bigger and bigger computers. It turned out that during a “hot war” back on earth the Americans and Russians dutifully went out and fired at each other with rifles. There were few casulties, but many of the bullets entered orbit. They needed the computers to calculate the orbits of the projectiles to predict when the next “bullet shower” was going to come by. As the bullets kept coming around and ricocheting off things, they needed bigger and bigger computers to calculate the more complicated orbits in time for the next “shower” ---
**Author:** ![Sofa\_King](https://avatars.discourse-cdn.com/v4/letter/s/58956e/32.png) [@Sofa\_King](https://boards.straightdope.com/u/Sofa_King)\ **Post date:** [August 4, 2000, 9:31pm UTC](https://boards.straightdope.com/t/would-a-bullet-travel-faster-on-the-moon/27835/34 "2000-08-04T21:31:00Z")
Wow. It’s amazing what fruit can drop from the tree of knowledge when there are enough people to shake it. I read that story, too, when I was about ten years old, and had completely forgotten it until you mentioned it, KeithB. I don’t remember the title of the short story, but it was in a book called _Combat SF_. ---
**Author:** ![Padeye](https://avatars.discourse-cdn.com/v4/letter/p/a9a28c/32.png) [@Padeye](https://boards.straightdope.com/u/Padeye)\ **Post date:** [August 4, 2000, 11:09pm UTC](https://boards.straightdope.com/t/would-a-bullet-travel-faster-on-the-moon/27835/35 "2000-08-04T23:09:44Z")
> [@](#): > > \*Originally posted by Triskadecamus \* > **…initial velocity is much more strongly affected by the _differential_ pressure between the firing chamber, and the barrel. With no atmosphere at all that differential is a lot greater.** It could make a difference but I doubt a measurable one. Sea level atmosphere pressure is less than 15lb/inch^2 Chamber pressures of rifle cartridge can be in the neighborhood of 50,000 psi. Even with a low pressure handgun round like .45 ACP with around a third the pressure, atmosphere pressure isn’t too significant. ---
**Author:** ![Boris\_B](https://avatars.discourse-cdn.com/v4/letter/b/fbc32d/32.png) [@Boris\_B](https://boards.straightdope.com/u/Boris_B)\ **Post date:** [August 4, 2000, 11:38pm UTC](https://boards.straightdope.com/t/would-a-bullet-travel-faster-on-the-moon/27835/36 "2000-08-04T23:38:24Z")
**Joe\_Cool** You’re right about .22 LR usually being supersonic. I think when people mention it is a quiet round, they mean that its subsonic loads are even quieter than other subsonic loads, since it’s just a small cartridge with a small propellant charge. One of the reasons people mention .45 ACP so often as one of the supposedly rare subsonic rounds, is that most other subsonic rounds are designed for revolvers. Why would you want a subsonic round? To be quiet. How to be really quiet? Add a suppressor, which doesn’t work with revolvers with their barrel-cylinder gap. So really, what people are saying when they mention .45 ACP is, it’s the only commonly available, reasonably powerful, subsonic round which is designed for autoloading weapons. It’s not really true any more (c.f. 10mm FBI lite, .300 Whisper, the subsonic nines), but it was during World War II (the British even had bolt-action “silent carbines” chambered for .45 ACP - you can’t get much quieter than that). Talk about getting off topic… ---
**Author:** ![Silo](https://avatars.discourse-cdn.com/v4/letter/s/ac91a4/32.png) [@Silo](https://boards.straightdope.com/u/Silo)\ **Post date:** [August 5, 2000, 3:30am UTC](https://boards.straightdope.com/t/would-a-bullet-travel-faster-on-the-moon/27835/37 "2000-08-05T03:30:13Z")
I thought just for fun I’d calculate how far a bullet would travel if fired on the moon. For “maximum horizontal distance” I calculated the bullet to be fired at 45 degrees. And I set the velocity of the bullet at 1,000 m/s. Now gravity on the moon is 1.62 m/s^2. Sooo, ((1,000m/s)^2) / (1.62m/s^2) = 617,284m. 617,284m = 2,025,309 ft = 383 miles (damn!) Now the radius of the moon is 1.74 x 10^6 (m). So the distance around the moon is 2 pi (1.74 x 10^6) which = 10,932,742m = 6,793 miles. So that bullet would travel roughly 1/17.7ths of it’s way around the moon. ---
**Author:** ![Triskadecamus](https://avatars.discourse-cdn.com/v4/letter/t/b19c9b/32.png) [@Triskadecamus](https://boards.straightdope.com/u/Triskadecamus)\ **Post date:** [August 5, 2000, 4:46am UTC](https://boards.straightdope.com/t/would-a-bullet-travel-faster-on-the-moon/27835/38 "2000-08-05T04:46:33Z")
> [@](#): > > \*Originally posted by Padeye \* > It could make a difference but I doubt a measurable one. Sea level atmosphere pressure is less than 15lb/inch^2 Chamber pressures of rifle cartridge can be in the neighborhood of 50,000 psi. Even with a low pressure handgun round like .45 ACP with around a third the pressure, atmosphere pressure isn’t too significant. With a supersonic (OK, on the moon, make that “very fast”) round, atmospheric pressure is not the end of the story. The air in the barrel can’t get out of the way. It piles up in front of the bullet and exerts a force against it which increases directly as the expansion of gasses from the charge decreases down the length of the barrel of the gun. Without this effect a long barreled weapon would be far more effective in converting the energy of the propellant charge into kinetic energy. Tris ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [August 5, 2000, 6:51pm UTC](https://boards.straightdope.com/t/would-a-bullet-travel-faster-on-the-moon/27835/39 "2000-08-05T18:51:10Z")
can’t find the actual link I need, but this one provided something [http://explorezone.com/space/moon.htm](http://explorezone.com/space/moon.htm) 'The Moon has almost no atmosphere, ’ which means it has some. so using this, I conclude that 1: there is a speed of sound up there, and 2 low moon orbit is not stable due to the atmosphere, where low means shoulder height above the higest moon mountain. The link I was looking for talks about the moons atmosphere which ranges from barely measurable (on the side away from the sun) to still very thin (sunny side) and is made up of, mainly some kind of silicon vapor. ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [August 5, 2000, 6:54pm UTC](https://boards.straightdope.com/t/would-a-bullet-travel-faster-on-the-moon/27835/40 "2000-08-05T18:54:29Z")
strike silicon and put in sodium here’s the link [http://explorezone.com/archives/99\_06/04\_moon\_tail.htm](http://explorezone.com/archives/99_06/04_moon_tail.htm) [Previous page](https://boards.straightdope.com/t/would-a-bullet-travel-faster-on-the-moon/27835.md?page=1) [Next page](https://boards.straightdope.com/t/would-a-bullet-travel-faster-on-the-moon/27835.md?page=3)