Ballistics 101

I love ballistics and the science behind it.   It has to be one of most complicated things in the world because it has so many factors that contribute to how it works.  What is ballistics anyway?  Ballistics refers to the mechanics that deal with the flight, behavior, and effects of a projectile (bullet) when moving.  Sounds simple enough? Not really.  Ballistics is how a bullet reacts to its environment as it travels.  I love the study of ballistics and use to study charts when I was a Marine.  I studied ballistics further then most snipers ever dreamed.  I was an infantry mortar man and specialized in the 60mm mortars.  The weapon has a max effective range of over 2 miles (I can tell you exactly, but would have to kill you, just kidding I’m just not going to post exact data of US weapons’ capabilities here just to be on the safe side).  The weapon also had a max ord (height the round travels to) of over 6,000 feet.  I learned all the formulas, charts, and calculations associated with this and then, because it would take a super computer to input all the variables, gave a SWAG (Scientific Wild A.. Guess) as to the location the round would impact.  I got really good at it.  So when I moved to rifles, it wasn’t hard.  A lot of the formulas transfer over and the distances aren’t as great, but the targets are smaller.

Anyways, back to ballistics.  As a general rule there are three types or ballistics associated with guns; internal, external, and terminal.  Internal ballistics is the shortest time and only covers the time the bullet moves through the barrel.  Once out of the barrel the bullet is now into external ballistics.  Once the bullet hits something (hopefully its target) it becomes terminal ballistics.

I love internal ballistics, but it’s really a geek’s world because there isn’t much people can do about it.  Internally it’s all about how the bullet accelerates down the barrel, how it twists, and how fast it is going when it leaves the barrel.  The bullet twists so it stabilizes in flight.  Think of it like a football.  When it spins it stays point first and goes further and is more accurate.  If a football is kicked and there is no spin, it goes end over end.  A bullet will do the same thing, so the barrel spins it.  The speed is important so we can calculate all the external ballistic stuff, and is easily measured by shooting the gun over a chronograph (contraption that measure how fast the bullet is traveling).

Once the bullet leaves the barrel then external ballistics are in, this is where everything in the environment kicks in, wind, rain, barometric pressure, heat, gravity (the biggest one), fog, heat off of the ground, and even the spin of the earth.  See why it would take a super computer to calculate this stuff.  Gravity has the biggest effect.  As soon as the bullet leaves the barrel gravity takes effect and starts pulling the bullet towards the earth.  Fun fact; if you fire a gun exactly parallel to the ground and drop a bullet at the same time the bullet leaves the barrel; both bullets will hit the ground at the same time.   The bullet may appear to rise, but it doesn’t.  See illustration

The bullet’s path is called the trajectory.  Line of sight is how the sights or scope is set on the rifle.  Where the line of sight and trajectory crosses is the zero for the rifle (point of aim and point of impact are the same).  On rifles you can actually have 2 zeros.  As the bullet leaves it is shot up and arches down so it passes the line of sight twice.  This photo is out of an old training manual where the M16 was zeroed at 300 meters and 33 meters.  We use to cheat in the Marine Corps and set targets at 33 meters and zero our rifles.  The trajectory of any bullet can now be calculated very easily by a computer and there are tons of online things that do it (there is even an app for that).  All the other factors are a lot harder to calculate because they aren’t constant.  None of this matters until you get good and are shooting at longer distances.  The Marine Corps even teaching that wind isn’t a factor when shooting the M16 until past 200 meters.

Once the bullet strikes something we are into terminal ballistics.  Most of this study has to do with living tissue.  Hunters want to know what the bullet will do once it strikes an animal, militaries want to know what the bullet will do in people, and self defense people are interested in stopping someone.  Like external ballistics there are just too many variables for anything to be perfect.  We use computer models to create different bullet designs and then shoot the bullets into different mediums to see what it will do.  There are so many factors that I can say for almost 100% certainty that no two bullets fired out of the same gun, on the same day, at the same target, will do the same thing.  The normal things that companies measure are expansion and penetration.  People want to know how much the bullet will deform and how far into the target the bullet will go before stopping.  All bullets will deform and bullet designers try to use that fact to make the bullet get bigger so theoretically it will do more damage.  I say theoretically because nothing will ever happen the same exact way twice.

See how complex this gets.  This is by no means a comprehensive post on ballistics but just a start on how it works.  In future posts I’ll go into more depth about each part just for some of those people that are geeky like me.

Stay Safe,

Ben