Free-falling bullets

There is an age old tradition in some cultures to fire celebratory shots into the air on certain anniversaries, events (weddings), or accidents. In the United States this activity seems more concentrated around our Independence day and New Year’s Eve (although pretty rare overall). For the purposes of this posting we’ll just consider bullets fired from small arms as opposed to artillery shells.  Bullets falling from the sky are no laughing matter. They can cause serious injury including death. But, there are some misconceptions surrounding the lethality and velocity of bullets returning to Earth.

One of the most common misconceptions is that small arms bullets will return to the ground at the same, or greater, velocity than when emerging from the muzzle of the weapon. Now bullets come in a variety of sizes (caliber) and shapes. Basically they are conical in shape but the nose can be flattened or rounded as can the base (to a lesser degree). Believe it or not a number of studies have been conducted on this issue since at least the early twentieth century. It was found that some common rifle calibers such as the .30-06 attained a muzzle velocity of 2700 feet per second and gained an elevation of 9,000 feet. When a bullet is fired straight up into the air it will continue on it’s flight path until it is overtaken by gravity and begins to free-fall back to Earth.

During this fall the bullet will be affected by air resistance. Now it is theoretically possible the bullet can return one of three ways; nose first, base first, or tumbling. Of the three, a nose first return from a near-vertical trajectory is the least likely. It is much more likely that the bullet will tumble or fall back in generally the same orientation (so base first) especially if it retains any of the gyroscopic spin imparted from the barrel (rifling). Tumbling creates the greatest amount of air resistance so the bullet’s terminal velocity will be lowest in this condition. Regardless, most lead core bullets will return to the Earth in about 45-55 seconds. The falling velocity will be determined by a number of factors including the air resistance and bullet weight. Generally speaking, a smaller bullet like a .22 short will have a lower free falling velocity than a larger one like a .30-06.

While the muzzle velocity for most small arms can average around 1,000 feet per second that same bullet may only reach a free-falling velocity of 150-250 feet per second. If you consider that a bullet needs to reach a velocity of approximately 200-330 feet per second to perforate human skin in a nose first orientation you can see how these falling bullets may not cause a fatal wound. The key words being “may not”. There are plenty of case studies of people being killed by  downward arching bullets (though some are not at near vertical falling angles. They can still be very dangerous and cause serious injury. They will typically cause less trauma than one fired at close range however.

Reconstructing the original trajectory is nearly impossible because of all the conditions (wind, air resistance, tumbling, original load conditions, etc.) during flight that can alter the bullet path.  So if you are thinking about using a falling bullet in your novel you might want to keep some of this in mind. A falling bullet might only pierce the skin or in some cases just create a bruise. In other cases it may actually cause death. The important thing to remember is that they are not traveling at the manufacturer’s listed muzzle velocity. It should go without saying that you should never attempt to conduct this type of research or experiment. All of the published studies I am aware of were conducted by the military on large scale controlled firing ranges. Do not try.