Freefalling Bullets
Here is something which Dropzone.com readers may find interesting. This
write-up comes from something I did several years ago, which I discussed on
an aviation forum at the time. I'm posting it here for skydivers to read,
enjoy and comment upon.
Every July 4th and New Year's Eve, the subject of people shooting guns into
the air comes up for debate. On such holiday occassions, there is sometimes
a news story of someone being killed by "falling bullets", and policemen
parking their patrol cars under bridges to avoid the deluge. The discussion
surrounding this practice centers around the danger to people who may be hit
by descending bullets.
There is a great deal of disagreement over the speed of a freefalling bullet
and its ability to kill someone. Opinions on freefall speed vary from
anywhere between 100 to 400 mph! Some guesses are just "gut instincts" and
some were from sophisticated computer ballistics programs. There were also
some descriptions from "Hatcher's Notebooks" - Hatcher was an Army officer
that did numerous experiments with guns and ammunition. Well, I conducted a
personal experiment once, which may shed some direct light on this subject!
I am a skydiver with over 4,000 jumps experience, and I'm also an
experienced shooter. I combined these two interests in an, admittedly very
unscientific, experiment. I wanted to estimate the freefall speeds of
various bullets by taking them out of an airplane with me on a skydive,
releasing them in freefall, and seeing which direction they went, up or
down, relative to my own 120 mph terminal velocity.
The four bullets in the experiment, and their weights, were:
#1 .22 rimfire, 25 grains
#2 .223, 55 grains
#3 9mm, 115 grains
#4 .45, 230 grains
Note: a grain is a unit of weight with 437.5 grains to an ounce.
This provided a wide range of weights, sizes and shapes for comparison. As I
prepared to exit the plane, I pinched the .22 bullet between the index
finger and thumb of my left hand, the .223 likewise in my right hand, the
9mm cupped in the palm of my left hand by the outside three fingers, and
finally, the .45 cupped likewise in my right hand. The plan was to release
the bullets one at a time, from lightest to heaviest, and observe their
freefall velocity. Freefall from 13,500 feet provides 70 seconds of working
time, with the first 12 seconds used to accelerate to 120 mph, at which time
my freefall acceleration tops-out at 120 mph and increases no further. This
would allow a good 10 seconds to observe each bullet in turn as it was
released.
I spotted myself over the middle of a very large, wide open, uninhabited
field, exited the plane and assumed a face-to-earth body position. I waited
12 seconds to reach my terminal velocity of 120 mph, held out my left hand
in front of me, and opened up my index finger and thumb and released the .22
25-grain bullet. The bullet rose "up" rapidly relative to my own 120 mph
speed. It took only about two seconds for it to disappear out of sight above
me.
Next I stuck out my right hand into the solid air in front of me (avoiding
the low pressure over my back) and released the .223, 55-grain bullet. It
too rose "up", but not quite as fast as the .22.
Third, I released the 9mm, 115-grain bullet. Likewise, it too rose up and
vanished out of sight above me, but took much longer than the first two
bullets. It's rise was fairly slow.
Finally (I'm really having fun now!) I released the .45, 230-grain bullet.
This one stayed with me in perfect synchronization with my 120 mph fall. I
actually flew in formation with it for about 20 seconds! It was tumbling
end-over-end wildly and the nose and tail were just a blur, while the center
appeared solid to my vision.
At this point, I tracked horizontally to get out from under these four
falling bullets, opened my parachute, and floated back down to the landing
area with a big smile on my face, thinking about the interesting results.
My conclusion, based upon actual freefall with these projectiles, is:
Speed of .22, 25-grain - about 60-80 mph
Speed of .223, 55-grain - about 80-100 mph
Speed of 9mm, 115-grain - about 100-110 mph
Speed of .45, 230-grain - 120 mph
There you have it: direct observation evidence. The folks with the ballistic
programs had me believing 300 mph, until now. Hatcher concluded a speed of
200 mph for .30 caliber 150 grain bullets, but this was computed based upon
math using the initial muzzel velocity and the time it took bullets to
return to earth. My experiment is not very scientific, but I believe what I
see with my own eyes.
One flaw in my test is that I was unable to spin-stabilize the bullets, in
the manner in which they would be oriented if fired from a gun. So the
terminal velocity of a bullet tumbling end-over-end may be different from
that of a bullet which is spin-stabilized in freefall, falling nose or tail
first.
The Army considers 60-foot-pounds of energy the amount necessary to produce
a disabling injury with a bullet. Even using Hatcher's speed of 200 mph,
that freefall speed would produce only 30 ft-lbs.
So, my conclusion is, contrary to popular myth, that if you are hit by a
falling bullet, it will not kill you. More likely, it's just going to sting
like hell. This does not apply to shots fired at an angle to produce an arc
trajectory, whereby much of the horizontal velocity is retained by the time
the bullet reaches the ground again.
Despite these conclusions, I am not encouraging anyone to go out and shoot
their guns straight up into the air!
Comments?
. traditionally shooting up in to the air and at times bullets will fall out of the skies and actually injure AND kill people. Accidents at the Weddings...
