Tag Archives: muzzle velocity

Ballistics 101

What is “Ballistics?” “What is Muzzle velocity?” “What is ft/lbs energy?” “How does barrel length effect muzzle velocity”? “Do bullets travel in straight lines”? “What does {point blank} mean”?

Simply put, “Ballistics” is just a MEASURE of a bullet performance-when it leaves the gun (internal ballistics), while it is in flight (external ballistics), and when it impacts a target (terminal ballistics). Let’s take a look at these categories AND how to judge a bullet’s performance based on looking at its “ballistics”.

Internal Ballistics

Internal Ballistics is a numerical value that has to do with PROPULSION and ACCELERATION. You usually see Internal ballistics expressed in terms of “Muzzle Velocity” and “ft/lbs” of energy. The muzzle velocity is measured by a radar device that sits a few feet in front of the gun. GENERAL RULE of THUMB. The longer the barrel, the higher the muzzle velocity for a particular caliber. For example, the muzzle velocity of a 9mm being shot out of a 5 inch barrel will be HIGHER than the same bullet being shot out of a 3 inch barrel. This is occurs because of two basic reasons.  Firstly, the bullet is no longer assisted by the spiral grooves inside of the barrel once it exits the barrel. Once the bullet leaves the barrel it is relatively “independent” and is left at the mercy of the wind, GRAVITY, air friction, humidity etc. Secondly, the rapidly expanding gases inside the chamber also play a critical role in propulsion and acceleration. Once all of these high pressure gases are expelled, the bullet is left independent. Muzzle velocity IS THE FASTEST POINT at which the bullet will travel. The bullet will get slower as it flies down range (just like a football in flight).

Figure B1

Internal Ballistics Chart for common handgun calibers. NOTE. This ONLY gives you how the bullet behaves upon being propelled out of the gun. This is probably the most commonly referred to source of HANDGUN bullet power because handguns will be used at short ranges.

External Ballistics

External Ballistics is an observation of how a bullet behaves in flight. BULLETS DO NOT TRAVEL IN STRAIGHT LINES. (see figure B2 below) Bullets travel straight when leaving the gun, they rise, and then they begin to “drop”. GRAVITY IS A BULLET’S BIGGEST ENEMY. If you were to draw a line that represents a bullet’s flight path, it will look like a slight slope that gradually decreases downward as the distance increases (just like a football). The ultimate goal for a bullet is to maintain as much of its muzzle velocity as possible throughout its flight path. Every caliber has a different ability to fight gravity and air friction and stay airborne. Ballistics Coefficient (abbreviated “BC”) is a bullet’s ability to resist air friction and stay airborne. A high number means the bullet is more efficient at resisting air friction (negative acceleration). A high number also means that the bullet will retain MORE velocity as it moves down range.  Basically, BC is a measure of how Aerodynamic a bullet is. It is important to note that BC is merely a measure of a bullet’s ability to resist air friction. A high BC is NOT an indicator of how “good”  a round is.

Figure B2

Bullet trajectory of a .223 Remington (AR-15 bullet) out to 200 yards. NOTE. Bullet DOES NOT travel in a straight line.

Figure B3

.40 S&W (180 gr) on Left and .50BMG (750 gr) on right. Can you guess which round has a higher BC? If you guessed the one on the right you are correct. Just look at the shapes. Which one looks more aerodynamic? The .40 S&W has a BC of .164. The .50 BMG has a BC of 1.050. According to these numbers the .50 BMG is nearly 10 times as efficient as resiting air friction than the .40 S&W. Source http://www.hornady.com/store/50-BMG-750-gr-A-MAX-Match/

Bullet Drop

An important subset of External ballistics measures bullet trajectory-Bullet Drop. Simply put, “Bullet Drop” is a set of figures, either expressed in a line graph or a numerical chart, that illustrates the effect that gravity has on a particular bullet at various ranges. You may hear an experienced shooter compliment a round a say it shoots “flat”.  “Flat” simply means that the bullet has an efficient trajectory and resists gravity and air effectively.  Bullet drop charts are especially important for hunters, competitive shooters, and police/military snipers. For instance, a .300 Winchester Magnum may shoot “flat” out to 320 yards. This 320 yard distance is called “Point Blank Range”. Point blank range is the MAXIMUM “can’t miss distance” for a particular round. Beyond 320 yards, this round may start to “drop” (For instance the drop rate may be -6 inches at 600 yards). To compensate for this, an experienced shooter will have to aim HIGHER than the intended impact point in order for the bullet to hit on the desired location. Every bullet has its own unique drop rate. These unique drop rates are also influenced by humidity, wind, elevation, barrel length, bullet weight and bullet composition.

Fig B4

Bullet drop chart for common large game hunting cartridges. “300”, “600” etc indicate distance. -1.1, -7.5 etc indicate bullet drop rate at a particular distance. Question. What is the bullet drop rate for the 338 Lapua at 900 yards? The correct answer is -20.8 inches. This means in order to hit the desired target, the shooter needs to aim at least 20.8 inches HIGH. If the shooter doesn’t aim high enough, the round will simply bury itself in the dirt. (Just like a quarterback needing to LOB a football 60 yrds instead of throwing it straight).

Terminal Ballistics

Terminal ballistics is the study of how a bullet behaves when it impacts its target. Velocity, bullet type (soft point, hollow point, rifle, flat point, round nose), and target type all play important factors in terminal ballistics of a round. This is an EXTREMELY broad subject. For our purposes we will focus on basic characteristics of common rounds and how they behave. Panthera Armory believes in the utilization of visual observation as a learning tool. Ever heard of “ballistics gel tests”? These tests, even though they can be flawed, vividly illustrate how rounds behave when they hit soft tissue.

Video B1

This is how an Full Metal Jacket .45ACP behaves. The blunt shape of this round makes it go “through and through”.

Video B2

This is how the AR-15 bullet behaves. Notice how the round tumbles. This is called the “Yaw” effect. Other experts call it the “boomerang effect”. This is common among rifle rounds because of their high velocity. The yaw effect is responsible for causing massive trauma to surrounding tissues. This is how such a small rifle round such as the 5.56 can cause impressive terminal ballistics.

If you need further research on TERMINAL Ballistics Check out Brass Fetcher on youtube. By far the BEST slow motion close up Ballistic gelatin tests on youtube. You see the bullets deform and the gel oscillate from the kinetic energy transfer.