If I fired a 9mm bullet in the air?

I don't know the answer to any of your questions! But it made me think.........if you did shoot a gun straight into the air, on a windless day, would the bullet drop straight back down the barrell of the gun?

In theory (neglecting air resistance), the bullet will fall to Earth with the velocity with which it was fired. Despite a bullets small size of just 9mm it would actually suffer significant air resistance due to its high velocity.

It turns out that the terminal velocity of a bullet isn't fast enough to be fatal. Another interesting point is that the bullet would fall blunt end first, because it is more stable that way. Also due to a bullets small mass it is easily affected by wind, and even if shot vertically it would probably land 100's of meters away from where it was shot.

I don't know about the last bit, but I would say being shot by someone who's several hundred meters away is pretty unlikely, although possible. A considerable amount of people do get killed by bullets not intended for them however (for example, aiming for the person next to them and missing).

Mythbusters on Discovery tested this very thing with a 9x19 (fired from a Glock, I think), and a 30-06.

If the bullet went straight up, it would come down no faster than its terminal speed (which was found to be about 100mph). Some shots were fired at this speed into a pig's head and were found to cause only the slightest damage - no skull penetration at all, and only a faint mark on the scalp. It was certainly not lethal.

If the bullet was fired at a slightly TILTED angle, however, it would still be carrying a component of horizontal velocity, and would be far more likely to injure or kill somebody. There is a documented case of exactly this, and the shooter was prosecuted.

You would need to know the velocity of that particular load for your particular gun and the mass of the bullet to calculate the apogee.

The return velocity would be a constant speed within a few yards of reaching the maximum height.

A 9mm would have more than enough speed and mass to kill you just from the speed at terminal velocity. Since the damage would be to the head or upper body where loss of blood would likely be more profuse, the damage would be more likely to be fatal than if you were kneecapped or shot yourself in the foot.

The range of a 9mm is certainly less than two miles. I would think in a pistol the range would be far less than one mile.

Almost as many people are injured by bullets not intended to be lethal as are killed by bullets in which the intent is to kill. Only a very few people are killed accidentally by stray bullets.

As to whether a bullet might fall directly into the barrel from whence it came, it is unlikely that such a bullet would return from its maximum height without tumbling.

How high the bullet would go depends solely upon the muzzle velocity, the mass and barrel length effect the bullet before it leaves the barrel. Gravitational deceleration of -32ft/sec² (sorry, don't know the SI units) will decelerate the bullet until it stops rising then it will accelerate at the same rate on it's downward path until reaching terminal velocity for that configuration.

Re stray bullets.

One of the basic rules about sporting shooting is to see your background, never shoot at anything where a miss would result in the bullet going beyond your range of vision and possibly causing death through negligence.

This is obviously not applicable in war.

A spent 9 mm falling straight down can injure. A bullet shot two miles would have to be of higher caliber though, like a hunting rifle. People do, on occasion, get killed by such bullets.

How high the bullet would go depends on the muzzle velocity of the gun. This is determined by the explosive charge in the bullet and the length of the barrel. The longer the barrel, the faster the muzzle velocity.

If it went straight up and straight down then it would tumble to earth under the influence of gravity alone and you would survive being hit. Any other way and the bullet would still have it's velocity and would also be affected by gravity and could hit and kill someone. They did this on Mythbusters, see if you can find it on Youtube.