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May 02, 2007

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What Goes Up. . .

If you watch any news program, you are bound to see footage of gun-toting militants in various parts of the world firing AKs heavenward in celebration or protest or whatever. But have you ever wondered what happens to all those Kalash slugs? Oddly enough, there was real scientific research performed on the subject by the U.S. Army Ordnance Corps between 1918 and 1920 by a young officer who would later become the noted firearms writer Major General Julian Hatcher

Here’s some of what the Army  found:

*The tests were conducted with a machine gun locked in a fixture that held the barrel vertically. The gun was sited so that the bullets would fall either on still water or on sand. The men doing the shooting were protected by armor over their heads.

*Using 150-grain service bullets, it was calculated that  the slugs would strike the earth with an energy of about 30 foot pounds. At the time, the Army believed that 60 foot-pounds were required to produce a disabling wound.

*On the downward trip, the bullets would reach a point where air resistance equaled the force of gravity. At this point, they were traveling at 300 fps, and they would not go any faster.

* At 9000 feet, at the apex of the bullet’s path, and for the first 16 feet of its fall, it is moving only 32 fps, giving the strong winds at this altitude plenty of time to push on it. Of 500 rounds fired from a 10-foot-square platform, only 4 struck it on the return trip. That’s why if you shoot a slug straight up, it will probably not crack your skull on the way down.

But it may crack someone else’s, so I advise against doing it.


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Ralph the Rifleman

I have read about similar tests, and the "Myth Busters" ( I know Dave, their gun handling practices scare you) had done a test as such using the 9mm I don't recall the exact ft-pounds/speed result but I am sure it was similar to these.
Last year, during the 4th of july holiday in a neighboring city, a person was struck by a falling bullet while sitting in her covered patio room. The bullet punched thru the exterior awning and struck her knee. Not a life threating wound, but it seems the bullet had enough power to cause serious injury if she had been sturck in the head!

Peter C

In 2000, the AZ legislature passed "Shannon's Law," a regulation making firing guns randomly in the air a felony. It was named after a young girl who was killed by a stray bullet that hit her in the head. Apparently, firing into the air is considered a celebratory act by certain cultures.

Dave in St Pete

The problem is NO ONE shoots perfectly straight up so you end up with a ballistic trajectory and a very deadly round coming back to earth.


Well Dave here is a thought:

I have had the following argument (numerous times).

When comparing to different cartridges……No matter the speed of the projectile when fired from a level surface (parallel to the ground) the bullet will always hit the ground at the same time. So if you fired two different guns (say 300 win and a .22) at the exact time, the bullet will impact the ground at the exact time…. Do you believe this?

Dave Petzal

To Tom: The heavier bullet would carry much farther and drop long after the .22 had fallen to earth. Greater weight, greater momentum. The same reason a 16-inch naval gun will outrange a 14-inch.


Ah, Dave. Are you certain of that drop? If I recall my physics, rate of drop is a constant 10-meters/sec square.


I always wondered when I saw those towel-wearing idiots on CNN shooting their AKs into the air. "Holy war! Holy War!" *plink, plink, plink* "Holy s***!"


I always wondered when I saw those towel-wearing idiots on CNN shooting their AKs into the air. "Holy war! Holy War!" *plink, plink, plink* "Holy s***!"

Dave Petzal

To Mark: No, I am not. If you, or anyone who is scientifically aptituded can add anything to this issue, have at it.


Dave, that is the answer I have debated. You could be right but here is my thoughts on the subject:

If you shoot a bullet at say 3000 feet per second and drop a bullet at the exact same time (from your hand) both bullets will hit the ground at the same time. It is gravity; gravity does not care if you are moving forward at 3000 feet per second or zero. As long as the bullet does not have “wings” or shaped like a “leaf” there is not resistance to keep it up.

With that being said if you include the parabolic arch (scope) you negate all of this.

Here is a note from a web-site:
“If you would shoot a bullet from a gun exactly parallel to the Earth's surface, the motion of the bullet would have no effect on how gravity acts on the bullet. In other words, the bullet would drop at the same rate as a stationary object.
Many people don't believe that if you held a rifle parallel to the ground and at the same time you shot the bullet, you dropped another bullet from the same height, that they would both hit the ground at the same time. This would be true even if the bullet shot from the gun traveled a great distance before hitting the ground.
You can try a simple experiment to verify this. Place a coin on the edge of a table or desk and hold another coin at the same height. With one hand flip the coin on the table across the room. At the same time, drop the other coin. You will or hear that they hit the floor at just about the same time.”

Instead of asking a scientist check this page out http://hyperphysics.phy-astr.gsu.edu/hbase/grav.html#bul

Chris Byrne

In order to it the ground at the same time, they would have to have the same vector.

If and two bullets were dropped straight don from the same height, they would in fact hit the ground at the same time.

However, this is not the case when two bullets are actually fired out of a gun; even if the centerline of the bore is perfectly perpendicular to gravity; because the force (actually forces) acting in the X axis, and the force acting in the y axis (graivty) prduce a vector that is NOT 10.8 meters per second per second straight down. Additionally, there is an aerodyanmic element to the forces in question that must be considered; as it effects bost the positive x axis and y axis forces (effectively adding negative x and negative y elements to the vector).

Whenever multiple forces meet, there is a vector that is the sum of those forces. In this case we have the force of the bullets propulsion, the force of gravity, the force of the air against the bullet, and the force of gyroscopic inertia (from the bullets rotation).

The resultant vector is dependent on the total force in each direction, which is dependent on the mass, velocity, and firing angle (or in the case of the gyroscopic forces rotatonal velocity) of each bullet; as well as local gravitational variation (gravity varies with altitude a ballistically significant amount), air pressure, temperature, and humidity (all ofwhich effect air density).

Now, these differences start off small, but the longer the bullet is in flight, the more they make a difference.

If you were to fire two guns perfectly horizontally from a standing position with 5000 feet of level ground in front of you for example, the bullets would in fact fall to earth at functionally the same time (a few microseconds difference perhaps).

However, if you fired from the edge of a canyon with 2 miles of clear space in front of you and a 5000 foot drop below you, the result would be very different.

This can be simulated with ballistic software if you'd like to take the trouble, but really it's just wonkery.



This is on the same site but you can calculate other trajectories. I can see your point Chris, but this is a debate that most people cannot agree on.

Paul Kowalski

That is why I put Hatcher's Notebook on my list of gunbooks in a post a while back.
Now, we are talking about bullets fired straight up and falling back to earth reaching terminal velocity.
With bullets (service weight) of 150 grains or less. Energy is about 30 foot pounds or less with lighter weight projectiles. Remember, 60 footpounds being necessary to achieve a serious wound. Most all stories about stray bullets have a hrizontal component to them making them dangerous and lethal.

That said, (again refering to Hatcher's Notebook, a artillery shell aor naval gun, fired straight up would also reach the terminal velocity, but do to it's weight, would really mess up your day.


"... but this is a debate that most people cannot agree on."

And that just means that many people are wrong -- physics is not a subject on which you get to vote. In the scenario of a bullet fired horizontal and one dropped vertically: Both will hit the ground at the same time. The links that Tom posted are worth serious study for anyone that is having trouble believing this.

To Chris: Vectors do indeed add to give a "resultant" vector. This does _not_ change the motion along any of the vectors though; it is common engineering analysis practice to resolve a vector into two orthogonal vectors that are parallel to the reference axis system. The simplification of ignoring air resistance will give the wrong _location_ for a horizontally fired projectile to hit the ground but has no effect on the vertical motion or the _timing_ of when it will hit the ground.

Mike Diehl

Here's the physics as best I recall it.

On earth the acceleration is 9.8 m/sec-sec. 10 is a ballpark approximation.

In a vacuum, two bullets of substantially different weights and at an identical and suborbital velocity would hit the ground at the same time. Thus the .22 would strike ground at the same instant as a heavier round.

That they don't is because in general drag robs energy from the .22 bullet faster than the larger bullet. Of course bullet shape, tumbling and all other manner of things can affect same.


Two bullets will drop at the same speed - in a vacuum. In reality, weight, shape, drag, etc., all come into play; hence different ranges for different rounds even at the same initial velocity/ angle, and different terminal velocities for different rounds fired straight up.

Remember, in theory, theory and practice are the same, in practice, they're different.


Two bullets will drop at the same speed - in a vacuum. In reality, weight, shape, drag, etc., all come into play; hence different ranges for different rounds even at the same initial velocity/ angle, and different terminal velocities for different rounds fired straight up.

Remember, in theory, theory and practice are the same, in practice, they're different.

OK, after typing this, I see the previous person said the same thing, so I 'second' his explanation.


OK, that's really odd, how did the previous post to mine get over-written. Must be a bug in the code here. Sorry Mr. Mike Diehl, it wasn't me!


I read all of you guy's smart-guy posts and tried the experiment for myself.

Shot the wife's vaccuum four times with no aparent difference in drop speed.

I do gotta buy a new vaccuum now.


Why is it her vacuum?

I don't think that you timed it correct. Was the vacuum on? If it was the centrifugal force and the electrons of the motor would cause a gravitational pull towards the motor thus casing a variance in the trajectory of the projectile. Also when it shot back did you count the drop time, as when the bullet was leaving the unnatural force it may cause it to drop faster.

Also did you put your beer down, as some beers are known to cause gravity (Jameson).



I would not want to be struck with a falling bullet returning to earth. the 30 Foot Pounds energy is similar to the recoil of a 300 Remington Ultra Magnum, but he diameter of the projectile is less than 0.45 inches. It would be like concentrating the recoil energy into a small stud on the stock. And on what part of your body would like to have this applied ?


The acceleration due to gravity is a constant, period. Air friction, rotational forces, and any other happy crap that you choose to spout off about do not change the time it takes for an object to fall from some point above the earths surface. Time being the important term here, not distance down range.


To all safe hunters and shooters, dont try this dumb stunt (shooting straigt up into the air), and seek safe shelter if anyone around you tries it. Leave it to the other cultures to perform this dumb stunt, and risk the well being of their citizens. If you aren't sure of the outcome, don't take the shot. Safe shooting, Richard V.T.


I always wondered about these heavenward shots. Now I know. Thank you for enlightenment.



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