Category Archives: Ballistics 101 Series

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.

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What is “caliber”? What is it a measure of?

“Whats a bigger caliber .40 or .380?” “Whats the difference between a 9mm and a .357?” “What does {caliber} mean?”

Caliber is basically the measure of the diameter of the projectile being fired. It is also a direct measurement of the diameter of the bore of a particular firearm. This measure can either be in fraction of an inch (i.e. .380) OR in millimeters (i.e. 9mm).

Common handgun calibers comparison

One common thing to remember in regards to caliber is that SOME calibers are not EXACT measurements. For instance, the .44 Remington magnum is NOT exactly .44 of an inch. It is closer to .429 of an inch than .44 of an inch. Another thing to remember about calibers is that we commonly see SAME caliber bullets stuffed in different size casings. For example, take a look at the figure above. If you did a little math, you will see that the .357 and the 9mm are the same diameter. The .40 S&W and the 10mm are also the same diameter. Let’s observe how this looks in a rifle example.

From left to right .308 Winchester, 30-06 Springfield, .300 Winchester Magnum (Missing is the Winchester 30-30, and the 300 Remington Ultra magnum)

These 5 cartridges are all in the “30 caliber family”. The projectile of ALL 5 of these cartridges measure’s .308 of an inch. These are essentially THE same SLUG stuffed in a different casing. “So which one is more powerful?” Take a wild guess between the 3 in the photo as to which one is more powerful. If you picked the one on the far right, you are correct. GENERAL RULE OF THUMB. Look at the size of the casing. The LARGER the casing, THE MORE gunpowder its going to hold. The MORE GUN POWDER the casing holds the faster the bullet is going to travel. The faster that bullet travels the more kinetic energy its going to have etc..

GRAIN-The STANDARD unit of Bullet weight measurement

You may hear or read of different bullets being 200 grains (often abbreviated “gr”), or 180 gr. This is the WEIGHT of the bullet/slug/projectile. For example, The .40 S&W is available in 135 gr, 155gr, 165 gr and 180 gr. Lets ask ourselves a few common sense questions and establish a few GENERAL ground rules (there are a few exceptions with high performance ammo manufacturers) 1. The LIGHTER the projectile, the higher the velocity (bullet will move faster through the air) but will not penetrate as deeply as a heavier projectile. 2. The HEAVIER the projectile the slower it will travel, but will work wonders when it comes to penetrating surfaces and retaining momentum. SOO..if you had a .40 S&W pistol with FMJ’s and you wanted to PUNCH THROUGH A WINDSHIELD (or sheet rock, or sheet metal, or plywood) and knock out a target in the front seat, which weight would you use? 135 gr or 180 gr? The 180 gr choice would be more practical. The slower moving 180 gr will retain MUCH more of its kinetic energy than the much FASTER moving 165 gr.

“Sooo…since a 230 gr .45ACP is a bigger bullet than the .357 Magnum which weighs 158 gr, is it more powerful?” The Answer is NO. Take a look at the figure below. 

.357 S&W Magnum (158 gr) on left .380 ACP (95 gr) in middle and .45 ACP (230gr) on right.

Obviously the .45ACP bullet diameter is wider than the .357 magnum. The .45 ACP also weighs more. SO…which one generates more power? To answer this question, Remember the GENERAL rule of thumb we previously discussed. That .357 magnum has a LOT more powder in its casing. This allows the .357’s 158 gr projectile to travel a LOT faster than the 230 gr .45 ACP. This considerable advantage in velocity allows the .357 to generate over TWICE the energy of the LARGER .45 ACP. GENERAL RULE OF THUMB…A LARGER DIAMETER CALIBER IS [NOT] ALWAYS MORE POWERFUL.