Justin A. Parr - Technologist

Guns are a pure expression of physics.

In addition to bad gun physics, movies and TV tend to depict handling or firing techniques that wouldn’t work, wouldn’t be effective, or could even be dangerous.

 

How Guns Work

A “cartridge” or “round” consists of a brass casing, partially-filled with gun powder, topped by a solid projectile.  At the base of the cartridge, there is a small reservoir that contains a primer cap.

People tend to use “bullet” and “cartridge” interchangeably, but “bullet” refers to just the solid projectile at the top of the cartridge, where “cartridge” refers to the fully-assembled round of ammunition.

In addition to the barrel, most guns have a hammer, a firing pin, and a trigger.  When you pull the trigger (1), it releases the spring-loaded hammer (2), which strikes the firing pin (3).  The firing pin strikes the cartridge’s primer (4), which then ignites the powder in the cartridge (5).  The exploding gun powder builds pressure very rapidly, propelling the bullet through the barrel (6), and eventually through the air to its target.

When a bullet is fired, the propellant powder exerts force on the bullet over a very short period of time, accelerating it very quickly.  While in the barrel, the bullet continues to accelerate, until it either leaves the barrel, or until the powder burns completely, at which time, the bullet follows a “ballistic”, arcing trajectory, where only gravity and air (and wind) act on the bullet until it hits an object or the ground.

 

Automatic Action

In the movies, “automatic” usually refers to “fully-automatic”.

Many handguns are “semi-automatic”, but a semi-automatic still uses an “automatic” action.

“Automatic” refers to a gun that, when fired, “automatically” ejects the spent shell case, and chambers an un-fired cartridge, leaving the gun ready to fire again.  Un-fired cartridges are stored in a magazine, where a spring-loaded follower pushes the stack of remaining bullets up, one at a time, as each one is loaded and then fired.

Looking from the top, an automatic gun has a slide or bolt that moves in the direction of the barrel, each time the gun is fired.

 

When the trigger is pulled (1), the hammer slams forward in to the firing pin (2), which fires the cartridge, resulting in the bullet being fired (3).  The recoil force or gas pressure pushes the slide or barrel backward, where the extractor removes the now-empty casing from the barrel (4).  As the slide or bolt continues to travel backward, the rim of the casing comes in to contact with the ejector, which causes the casing to pivot toward the extractor (5), resulting in the empty casing being ejected from the gun (6), revealing the next cartridge in the magazine, directly below it (7).  A strong spring, called the recoil spring, causes the bolt to travel forward towards its original position.  As the slide or bolt passes the magazine, it grabs the next cartridge and begins to load it (8).  As the slide completes its forward travel, the next cartridge is fully loaded, and the hammer is cocked (9), ready for the next round to be fired “automatically”.

Automatic action depends on either the gas generated by the exploding propellant (“gas operated”), or the direct recoil ( “blow back” ), to eject the empty case, and subsequently, load the next cartridge.

“Fully-automatic” refers to a gun that continues to fire as long as the trigger is held.  “Semi-automatic” fires just one bullet each time the trigger is pulled.

Most handguns are semi-automatic, not fully-automatic.

 

Revolver vs. Automatic

A revolver has a cylinder, with a hole or “chamber” for each bullet.

At any given time, one chamber aligns with the barrel.

When the trigger is pulled (1), the hammer strikes the firing pin (2) firing the  current round (3).  Cocking the hammer (4) rotates the cylinder, aligning the next chamber so that it’s cartridge is ready to fire.

 

Reloading

 

To reload a revolver, the operator releases a latch and swings the cylinder out to the left of the frame (1,2), exposing all cylinders.  Next, the operator points the barrel upward, and pushes the ejector rod, causing all of the empty brass to be ejected from the cylinder (3).  Once the operator has loaded a new round in each chamber (4,5), the final step is to swing the cylinder to the right, back in to the frame, where it latches (6).  A slight clockwise rotation aligns the next chamber and “locks” the cylinder in place.

Some English revolvers “break”, where the barrel and cylinder fold downward, resulting in the empty brass being forcibly-ejected by a spring-loaded ejector – these have a reputation for being slightly faster to reload, but the weaker frame structure is only braced at the bottom, and isn’t suitable for high-power cartridges.

In contrast, automatic handguns store their bullets in a removable magazine, and each round is loaded automatically, when the previous round is fired.

When the last round is fired, the slide typically locks back automatically (1).

The operator presses a latch or button to release the magazine (2), removes the empty magazine, then replaces it with a new, loaded magazine (2,3).

At this point, the magazine is loaded, but the chamber is empty (4).

If the slide is locked back, the operator presses the slide release lever, causing the slide to spring forward, chambering the first round from the magazine as it passes (5), leaving the hammer cocked and the gun is now ready to fire.

If the slide is closed (in its normal position), the operator must “rack” the slide (pull it backward, then quickly release it) after inserting a new magazine, in order to chamber the first round (4,5) and make the gun ready to fire (5).

Reloading Speed

In addition to capacity, automatics are generally faster to reload than revolvers.  Because an automatic’s bullets are already loaded in to a magazine, replacing the magazine takes only a few seconds, even for an inexperienced shooter.  In contrast, a revolver could take an inexperienced shooter 30 or 40 seconds to reload.

There is a magazine-like device for revolvers, called a “speed loader” or “speed assist”.  Like an automatic’s magazine, the bullets are held captive in the speed assist device.  During a reload, the speed assist allows the shooter to reload all of the revolver’s chambers simultaneously, rather than loading one bullet at a time.  Even with a speed assist device, which are normally only used  by police, reloading takes 10 to 15 seconds.

 

Capacity

While revolvers typically hold 5 or 6 rounds, automatics typically hold 7 to 15 rounds, depending upon the frame size and caliber.  A compact, small-caliber automatic might hold 6 or 7 rounds, where a full-size, medium-caliber automatic might hold 15 rounds.  High-caliber, large-frame automatics typically hold 7 to 10 rounds.

 

Unlike a revolver, certain automatic handguns can be fitted with a high-capacity submachinegun magazine that holds 20, 30, or more rounds.  For example, the Glock 17 (semi-auto, 9mm) normally holds 17 rounds, but it can be fitted with a Glock 18 (full auto) 33 round mag, providing almost double the capacity.

Automatics can be slimmer and more compact than revolvers, or they can have a superior cartridge capacity, but not both.  Also, automatics have a faster rate of fire, and shorter reload times.

 

Myth: Revolver Fires Too Many Bullets

Myth:  The bad guy has a big, scary-looking revolver, and fires 8, 10, or even 12 rounds without reloading.

Revolvers typically hold 6 rounds, although more powerful revolvers might only hold 5 – fewer chambers allows the wall of each chamber to be thicker, and thus stronger.  Some “camp” or “scout” revolvers of smaller caliber might hold up to 8 rounds.

Many large-caliber, compact revolvers only hold 5 rounds.  Occasionally, you’ll see the hero somehow fire 6 rounds from a gun that only holds 5!

 

Myth:  Revolvers are Powerful and Accurate

Myth:  Revolvers are typically depicted as more accurate or powerful than automatics

In reality, automatics are just as powerful and accurate, but quality plays a significant factor in any gun.  Most cheap guns, whether revolver or automatic, are inaccurate.  Likewise, poor quality ammunition can affect the reliability of automatics and revolvers alike.

Meanwhile, there are some powerful cartridges that can be used in either a revolver or an automatic.  Also, there are “high-power” cartridges designed for automatics, and others designed for revolvers.

For example, the .357 magnum round is usually a revolver round, but there are automatics chambered in .357 magnum, such as the Desert Eagle, or the LAR Grizzly.

Likewise, the 10mm auto cartridge has about the same power and ballistics as a .357 magnum.  Despite being designed for automatics, there are revolvers such as the S&W 610 that chamber the 10mm auto cartridge.

 

Fact: Reliability

Where a revolver shines over an automatic is reliability.  Although unlikely for a high-end automatic, any automatic can jam – for example, if the fired cartridge fails to eject, or if the cartridge bounces off of a wall, back in to the ejection port, the result is that the next round won’t load properly.

• Failure to Fire:  You pull the trigger, the hammer drops, you hear a “click”, and nothing happens.  This can be caused by old or faulty ammunition, but it’s more likely that the firing pin is worn, broken, obstructed, or frozen because it’s dirty or rusted. Unfortunately, revolvers CAN suffer from this condition as well, but this is unlikely to occur in any well-maintained gun.
• Failure to Feed:  You pull the trigger, but the next round doesn’t chamber properly.  This can be caused by a bad or bent magazine, a worn feed ramp, or even by bad ammunition that doesn’t push the slide back far enough.  Revolvers are always chambered, so this can’t happen to a revolver.
• Stovepipe:  This can happen if the ejector is worn, or with weak ammunition.  It can also be caused by shooting too close to an obstacle, where the empty case is deflected back in to the gun as it cycles.  Since revolvers don’t eject after each shot, they are immune.
• General Failure to Extract or Eject:  This can be caused by a dirty gun, worn or broken extractor, or worn or broken ejector.  Revolvers don’t extract or eject after each round is fired, so they are immune.
• Incomplete Battery:  The slide doesn’t close properly.  This can be caused by a dirty gun, a weak recoil spring, or ammunition (such as reloads) that are slightly out of spec.  Revolvers are always chambered, so this can’t happen to a revolver.
• Mag not seated:  When performing a reload under tactical conditions, it’s easy to fail to seat the magazine properly.  This is why you’ll often see the shooter give the bottom of the handle an extra tap after a reload.  If the magazine isn’t seated, it could cause the next round not to feed, or it could even cause the magazine to drop out on the floor when fired.  In addition, some guns have a magazine safety, such that the gun won’t fire unless there is a magazine inserted in to the gun.  Revolvers don’t have magazines.

As opposed to the recoil and spring forces, and careful timing required for an automatic to function properly, revolvers use a lockwork that mechanically positions the next round, making it ready to fire.  Although it’s possible for a revolver to jam, this can only be caused by a failure of the cartridge, or a failure of the lockwork, and thus a “revolver jam” is extremely unlikely.

 

 

It’s Not a Clip, It’s a Magazine

The good guy is running low on ammunition.  He calls to his buddy, to “throw him a spare clip”.

A “clip” is a thin piece of folded metal, where multiple bullets are slid in to the clip and connected by the rim.  A clip is designed to quickly reload a fixed box magazine, where the box magazine is a permanent part of the gun.  For example, the M1 had a fixed box magazine, and reloading the gun was performed by pushing a “clip” of ammunition down in to the magazine from the top.

Conversely, a “mag” or “magazine” (detachable box magazine) is a fully-enclosed box with a spring-loaded follower.  Each round is loaded from the top, pushing the rounds below it, and the follower downward.  As each round is fired, the gun loads the next round from the top, and the follower pushes the remaining rounds upward.

 

Myth:  Inserting a Magazine Chambers a Round

Myth:  The hero runs out of bullets.  He quickly ejects the empty magazine, inserts a fresh one, and continues firing.

As we’ve seen, unless there is already a round in the chamber, the operator must “rack” the slide (pull the slide all the way back, then quickly release it) in order for the bolt to grab a round from the new magazine and load it in to the chamber.  Racking the slide also cocks the hammer, making the gun ready to fire.

Most automatics lock the slide back after the last round is fired.  If this happens, the operator must push the slide release to chamber a round.  We only occasionally see the slide locked back after the last shot fires.

 

Myth:  A Submachinegun is a Small Machinegun

In TV and movies, we often see the two terms, “machinegun” and “submachinegun” used incorrectly or interchangeably, or the hero refers to a small machinegun as a submachinegun.

Generally, the term “machinegun” refers to a fully-automatic gun that fires rifle cartridges, while the term “submachinegun” refers to a fully-automatic gun that fires handgun cartridges, regardless of how compact the size.

A rifle cartridge is usually smaller in caliber, and higher in velocity.  The necked casing allows the round to hold more powder without increasing length or diameter.  Handgun cartridges are typically larger in caliber, but much lower-velocity.

For example, a full-auto AR-15 in a pistol configuration fires 5.56 x 45 rifle rounds, so it’s categorized as a machinegun, despite the fact that it’s extremely compact.  Likewise, despite the fact that an H&K MP5A2 has a fixed, wooden stock, and is actually quite large, it is categorized as a submachinegun because it fires 9 x 19 pistol cartridges.

 

Myth:  Dual-wield Submachineguns

In the movies, we see our hero emerge triumphantly, wielding a compact submachinegun in each hand, and then he fires, swinging his arms around energetically, instantly mowing down the bad guys with a swath of gunfire.

Despite what you see in movies, it’s not safe to operate a fully-automatic gun with one hand, regardless of what cartridge it fires.  In addition to the fact that you will probably miss your target, you also risk losing control of the gun, and injuring yourself or others.

Where the operator has to contend with recoil and muzzle flip from a single bullet fired from a normal gun, any fully-automatic gun produces multiple recoils, and has the tendency for the point of aim to quickly climb upward.

What makes this worse is that compact submachineguns generally have a much higher rate of fire, and can completely empty a high-capacity magazine in just a couple of seconds, which means that muzzle flip is much stronger, and that if the operator does lose control of the gun, several more rounds could fire automatically, before his finger has time to come off the trigger.

With lots of practice, it’s possible to learn to safely fire ONE compact submachinegun single-handedly, in short, controlled bursts.  However, swinging TWO of them around wildly would most likely result only in self-injury.

 

Machine Pistols

In the movies, the hero pulls out what appears to be a pistol, but it fires “full auto”

There are a few factory-built fully-automatic handguns, known as “machine pistols”:

• Glock 18:  Full-auto version of the Glock 17, 9mm handgun.  Notably used by:
  • Morpheus, Matrix Reloaded, during the freeway shootout
• Beretta 93R:  Full-auto version of the Baretta 92F, 9mm handgun.  Notably used by:
  • Robocop 1 & 2 (1990’s), Robocop’s handgun is a heavily-modified Beretta 93R
  • Chris Redfield, Resident Evil: Afterlife
  • Deakins, Broken Arrow
• H&K VP70M:  Just like the VP70Z, 9mm, but is capable of firing a 3-round burst when the external stock is attached.  Notably used by:
  • Gorman, Aliens
  • Frost, Aliens

 

 

Myth:  Firing Single Action / Hammer Down, or Firing With the Safety Engaged

“Single Action” (SA) pistols require the shooter to pull the hammer back, “cocking” the hammer, and priming the trigger.  With the hammer down, the trigger does nothing.

Examples of single action pistols:

• Colt Single Action Army (SAA) Revolver.
• Colt 1911 Semi-Automatic.
• Browning Hi-Power Semi-Automatic.
• IMI Desert Eagle Semi-Automatic.

“Double Action” (DA) pistols automatically cock the hammer when the trigger is pulled.  Even with the hammer down, if a round is chambered, pulling the trigger fires the round.

Most DA pistols allow both SA and DA modes of firing, where you can pull the hammer back (SA) for a more accurate shot, or simply rely on DA mode, and pull the trigger.

A DA pistol typically has a much longer trigger pull, because the shooter is using the trigger to pull the hammer back.  Conversely, an SA pistol has a much shorter, crisper trigger pull, because the sole function of the trigger is simply to release the hammer.  If the hammer isn’t “cocked”, the trigger does nothing.

The purpose of a safety, usually a button or lever on the side of the gun, is to block the trigger and prevent the gun from being fired.

Scene:  The action hero pops off several rounds, and the camera cuts to a quick closeup of the hero holding the gun, only to reveal that it couldn’t have fired, either because the safety is on, or because it’s a single-action pistol, and the hammer is down.

When you see someone firing a semi-automatic pistol on TV or in a movie, look carefully at the hammer and safety.  If the hammer isn’t pulled back on a single action handgun, or the safety is engaged on any gun, then the gun isn’t really ready to fire, and could not have just been fired!

 

Cocking the Hammer or Racking the Slide for Dramatic Effect

Scene 1:  Our hero has his gun pointed at the bad guy.  The bad guy refuses to surrender, so our hero racks the slide on his semi-auto pistol, to demonstrate that he’s serious.

Just… no.

• If the gun WAS chambered, the hero just ejected an unfired round that he might need later.  The gun is now in the same state before he racked the slide – chambered and ready to fire, but now there is an unspent cartridge on the floor somewhere.
• If the gun was NOT chambered, then the gun could not possibly have been fired prior to chambering, and the threat of being shot was hollow to begin with.  The bad guy could have simply (at a leisurely pace) pulled his gun and shot the hero before he had time to rack the slide, aim, and fire.

Scene 2:  Our hero has his 1911 pistol pointed at the bad guy.  The bad guy refuses to surrender, so our hero cocks the hammer of his pistol, to demonstrate that he’s serious.

The Colt 1911, Browning Hi-Power, and Colt Single-Action Army are all examples of single-action pistols that will not fire unless the hammer is already cocked.

• IF the hero’s gun is double-action, then cocking the hammer means a more accurate shot.  That’s menacing.  That comes across as a threat.
• If the hero’s gun is single action, then it was never ready to fire in the first place!  A single action pistol requires that the shooter cock the hammer before firing.  Pointing an unready weapon at someone is not a threat.  There’s always the chance that the bad guy could pull a chambered Glock and kill the hero before he has time to cock the hammer, aim, and fire.

 

Incorrect Sound Effect

There are three basic gun sound effects, other than the actual gunfire:

• Racking the slide to load a round:  The shooter sharply pulls the slide back, with a mechanical “CHICK”, then releases it, allowing the slide to load a round and slide in to battery with another mechanical “CHICK”.  When racking the slide, you hear “CHICK CHICK” or sometimes “KA CHICK CHICK”.  If the slide is locked back after firing the last round, the hero loads a new magazine and presses the slide release, “CHICK”, bringing the gun in to battery.
• Reloading an automatic:  The magazine makes a mechanical “SHHH” sound as it slides against the magazine well.  If it hits the ground, you might hear “SHHH CLUNK”.  When the shooter loads a new magazine, you hear “SHHH CLICK” as the magazine locks in to place.  If he presses the slide release, you hear “CHICK” to bring the gun in to battery.
• Cocking the Hammer:  The shooter pulls the hammer back.  The gun’s lockwork normally has two hammer positions, so you hear “click CLICK”.  If the gun is already at half-cock (the hammer’s safe position), all you hear is “CLICK”.  If the gun is a revolver, you might hear the mechanical lockwork advancing the cylinder to align the next chamber, and you would hear “click click CLICK”.

Scene 1:  The hero menacingly points his gun at the bad guy.  We hear “CHICK CHICK”, as if the hero racked his slide.

No.

Scene 2:  The hero inserts a new magazine, and we hear “CHICK CHICK”.

You would hear “SHHH CLUNK…CHICK”

Scene 3:  The hero draws his weapon from its holster, and we hear “CHICK CHICK”.

You would hear nothing except a rubbing noise as the gun exits its holster.  If he happened to pull the hammer back, you might hear “click CLICK” or “CLICK”.

Scene 4:  The hero pulls the hammer back “click CLICK” on his Glock or other hammerless pistol.

Glocks don’t have a hammer.  There is nothing to “cock”.  If you dry fire (pull the trigger on an empty chamber) a Glock, you hear “BOING” because a Glock has a striker instead of a hammer and firing pin.

Scene 5:  The hero pulls the hammer back on his Baretta 92, and you hear “CHICK CHICK”.

The sound editor has confused the hammer cock “click CLICK” with a slide rack “CHICK CHICK”.

 

 

 

Myth:  Fired or Ejected Cartridges

As we’ve seen, a “cartridge” is the fully-assembled round, consisting of a bullet at the tip, which is actually the part that flies off to hit the target, while the empty cartridge case is ejected out the side or top of the gun, landing on the ground near the shooter.

I’ve seen a few movies or TV shows where the prop guys clearly don’t understand how guns work.

Scene 1:  The Action hero wildly fires round after round at the bad guys.  The camera pans to the ground, showing a few, scattered, un-fired cartridges!

Scene 2:  The crime scene technician surveys the scene, and pries a fired “bullet” out of the wall, or discovers a spent “shell case” behind some furniture, but somehow manages to hold up a whole cartridge for the camera!

Scene 3:  The killer shoots the victim twice with a revolver, and immediately leaves.  Somehow, the crime scene technician finds an empty case that should still be sitting inside the gun, because revolvers don’t automatically eject spent cartridges.

Fortunately, most movies or shows with decent production values have the budget to hire a firearms adviser, who can help filter out these bullet mistakes.  Even though they are rare, when these mistakes happen, it makes the credibility laughable.

 

Myth:  Firing a Handgun “Gangster” Style

This shooting style seems to have originated in the 1990’s, where the shooter rotates the gun rotated to the left, firing it oriented horizontally.

This shooting style has a number of problems:

• The weapon’s sights are useless!  Normally, the sights are on top of the gun, adjusted to a specific elevation.  Firing it sideways, if you use the sights, would tend to put  your shots below and to the left of the target.  Rather than compensating for bullet drop and parallax as they are supposed to do, the sights are now compensating for gravity that’s now acting in the wrong direction.
• Sighting along the side of the slide is pointless.  You can’t aim accurately across a flat piece of metal.  Worse, if the slide is tapered, this will tend to push your point of aim above the target, where you might miss completely.
• Recoil and muzzle flip.  Normally, recoil pushes the gun back slightly, along the line of the barrel.  Because the barrel is usually located above the wrist when firing, recoil can produce “muzzle flip”, where the gun rotates upward when fired.  With the gun oriented to the left, the barrel will tend to flip to the left when fired, making a second, accurate shot much harder.
• Ejected cases.  Normally, empty cases are ejected either to the right and slightly behind the shooter, or out of the top.  If you fire a weapon that ejects to the right, rotated to the left, the empty cases will now hit you in the face.

As far as anyone can tell, the “gangster” shooting style originated as a Movie and TV myth, because no one who has ever actually fired a gun would decide to start shooting that way.

 

Myth:  Firing Guns Under Water

Firing Completely Submerged

Scene 1: In many movies and TV shows, we see a climactic underwater struggle between good and evil, where the gun goes off under water, killing hero or villain.

When you pull pull the trigger of a handgun, the hammer is released, which then strikes the firing pin, which strikes the primer of the cartridge.

In air, the hammer falls instantly, imparting all of its kinetic force directly in to the firing pin.

Under water, when the hammer is released, it must push the water out of its path, tremendously slowing the velocity, and thus the momentum of the hammer as it falls.

With a rifle, the hammer is usually internal.  Some rifles are designed to fire under any conditions, such as the AK-47, which will definitely fire when completely submerged, while others are not.

Any gun that’s not designed for rugged conditions may or may not fire when submerged.

Because of the reduced momentum of the hammer, many guns won’t strike the firing pin hard enough to fire the primer.

 

Fact: Glock pistols CAN be fired underwater

Note:  Glock pistols actually CAN fire under water.  No myth.  Glocks use a striker firing mechanism, rather than a traditional firing pin, meaning that the striker doesn’t depend on an external hammer.  Even a Glock won’t cycle under water, meaning, only the first round would fire.  Again, due to the mass of the water surrounding the slide, the force of the gas pushing backward would bleed off too rapidly, as the slide moves backward (pushing water out of the way as it goes), resulting in a failure to eject the spent cartridge, and a failure to load the next round.

 

Fact:  AK-47 / 74 rifles CAN be fired underwater

Note:  The AK platform is extremely reliable, and can be fired under a variety of conditions, including fully-submerged.  Again, due to the mass of water that the action must displace while firing, the AK will NOT fire fully-automatic, and may not even chamber the next round.

 

Firing In to Water

The above might give you a hint about the other part of this myth:

Scene 2:  The hero dives in to the water, as bad guys shoot at him.  Cutting to a view of the hero, we see bullets whiz past him.  In some movies, the hero incurs a trivial bullet wound trying to escape under water.

Just as the gun might not fire because the hammer has to move water out of the way as it falls, a bullet fired in to the water has to move water out of its way,and therefore loses kinetic energy.

With a specific gravity of 0.0013, air is 770 times LESS DENSE than water.  Lead, the primary component in bullets, is 11 times MORE dense than water, making lead almost 8,500 times more dense than air!  This means that air resistance is almost insignificant, as the bullet pushes air out of the way, only having an aggregate effect over long distances (such as when sniping or hunting).

Being much more dense than air, shooting in to water has an immediate and dramatic effect.  A bullet fired in to water has to displace 1/11 of its weight, for each bullet length.  Over just a few inches, most of the velocity (and therefore, the kinetic energy) is reduced to the point that a bullet hit would be insignificant.  It would be like throwing a bullet at someone by hand.  After a couple of feet, the bullet would lose all of its velocity.

You might say, “what about .50 AE”, one of the most powerful mass-produced handgun cartridges?

At a bullet length of just over 1 inch, with an initial muzzle velocity of 1,550 fps (Feet per second) the bullet drops below 200 feet per second, fired in to water, after a mere 22 inches.  At 200 fps, a bullet won’t kill you, but will leave one heck of a bruise.

How about a hunting cartridge, like the .308 Winchester, or what some might refer to as a “high power rifle” round?  At about 1 inch in length, with a muzzle velocity of 2,733 fps, the velocity drops below 200 fps at a mere 28 inches – just over 2 feet.

“OK”, you might say, “let’s step up to the BIG BOY”, .50 BMG.  .50 Browning Machine Gun is a scaled-up version of the .30-06 Springfield cartridge that had been used in the M1 Garand and the M1919 machine gun.  Designed to punch through light-armored vehicles, the bullet itself is about 2″ long, and with an impressive weight of 750 grains (almost 49 grams, or 1 – 3/4 oz) and a muzzle velocity of 2,820 fps.  Even the mighty 50 Browning would fall below 200 fps at a mere 56 inches (4.67 feet), fired in to water.

As long as the hero can swim more than three feet under water, and as long as the bad guys don’t have a .50 Browning machine gun, the hero is probably safe!

 

Firing From Under Water

The final part of this myth is firing FROM under water, with the barrel of the gun sticking out of the water, aimed at a target above water.

A gun’s barrel and action are designed to withstand immense pressure, as the bullet is fired, for fractions of a second.  Sustained pressure can cause the barrel to explode, or the action to split apart, which is why having any kind of obstruction in the barrel is basically the most dangerous situation you can face with a firearm (other than having someone shoot at you).

Firing a gun with an obstructed barrel can cause it to explode.

If you fire with the gun submerged, but the barrel above water, if there is water inside the barrel, the gun could explode.  By design, there is a tight fit between the chambered round and the barrel / chamber.  If there was a gap, it would allow gas to escape, thus reducing the energy imparted to the bullet, and severely reducing muzzle velocity.

The correct procedure is to tip the barrel downward to drain it.

If you suspect that there is mud in the barrel, the same situation can happen with any barrel obstruction, and the proper procedure is to disassemble the weapon to remove the obstruction.

If you fire a gun without draining the barrel, you won’t hit your target, and you might end up with a literal backfire!

 

Gun Designed to Fire Under Water

Trivia:  There is a firearm designed to fire under water.  The H&K P11 fires a 30 caliber, rocket-propelled steel dart, and is electrically-actuated (no hammer).  Unlike a ballistic cartridge, which receives force from the burning propellant only while the projectile is in the barrel, a rocket continues to provide force throughout the entire flight duration of the projectile.  Rather than losing momentum, a rocket-bullet can continue at a constant speed, or even accelerate despite the tremendous force exerted by the water (see Gyrojet).

 

Myth:  Bullet Impact Throws The Bad Guy Backward

Myth:  The good guy literally “blows the bad guy away”.  When hit with the fatal shot, the bad guy flies across the room.

A bullet weighs very little.  Bullet weight is typically measured in “grains”, and there are 7,000 grains per pound.  A lighter bullet, weighing 120 grains, weighs about 0.017 pounds (a mere 0.27 ounces), while a heavier 300 grain bullet weighs about 0.043 pounds (about 0.69 ounces).

On the other hand, bullets travel very fast.  The speed of a bullet, also known as the muzzle velocity, fired from a typical handgun ranges from 1,200 feet per second up to 2,500 feet per second, depending on bullet weight, load (amount of powder), and barrel length.

When a bullet strikes a target, we can describe the interaction with an array of formulas about force and acceleration, but the easiest is to use the law of conservation of momentum.  The combined momentum, which is mass times velocity, is same before and after the bullet strikes the target, because momentum is always conserved.

The law of conservation of momentum states that momentum before an event (p) is conserved after the event (p’):

p = p’

Before the event:

p = m * v

• p = momentum
• m = mass
• v = velocity

After the event:

p’ = m’ * v’

This gives us the equation:

m * v = m’ * v’

When we talk about two objects colliding (m1 and m2), we simply add up all of the individual components of momentum before the event (1, 2), which should equal the sum of all of the components of momentum after the event (3, 4):

m1 * v1 + m2 * v2 = m1 * v3 + m2 * v4

Assuming the mass stays relatively the same before and after the collision:

• m1 has velocity v1 before the collision, and v3 after the collision
• m2 has velocity v2 before the collision, and v4 after the collision
• To compute this, we have to convert everything in to slugs.  “Slug” is the unit of mass in the imperial system.  1 slug accelerated by gravity at 32 feet / s^2 results in a weight of 32 pounds.  Therefore, to find the mass of an object in slugs, take the weight in pounds, and divide by 32 feet / s^2
• m1 is the mass of the bullet.  Bullet weight is measured in grains, where there are 7,000 grains per pound.  Therefore a typical bullet weighing 150 grains is a weight of .021 pounds, or a mere 1/3 ounce.  Weight is not mass.  We then have to divide by 32 feet / s^2, the acceleration due to gravity, in order to find the mass in slugs.  A bullet weighing .021 pounds has a mass of 0.00066 slugs.
• m2 is the mass of the target.  Let’s say the bad guy weighs 160 pounds.  Dividing by 32 feet / s^2, a 160 pound man has the mass of 5 slugs.

As you can see, the bullet’s mass is tiny compared to its target, but bullets have a tremendous amount of energy due to their high velocity:

• v1 is the initial velocity of the bullet, which based on what we know about bullet velocities, we can set at a nominal value of 1,500 feet per second.
• v2 is the initial velocity of the target.  For simplicity, let’s say the bad guy is standing still, meaning the velocity (and therefore momentum) is 0.  Even if the bad guy is charging the hero at the time of the bullet impact (negative velocity), we can side step all of those messy mechanics by interpreting the result as a net change in velocity.  So, even though the bad guy has mass, we set his initial velocity is 0, and therefore his momentum is 0:
  v2 = 0
  m2 * v2 = 0
• v3 and v4 are the velocity of the bullet and target (respectively), after the impact.  Assuming that the bullet lodges inside the bad guy, their velocities are the same, therefore:
  v3 = v4

Simplifying the equation based on our assumptions, we have the following:

m1 * v1 = (m1 + m2) * v3

Because the bullet’s mass is insignificant compared to the target, we can further simplify by “zeroing” it out, after the collision:

m1 * v1 = m2 * v3

Because the bad guy isn’t moving before the collision, our only input is the bullet’s momentum, and the bad guy’s mass.

Because the bullet mass is insignificant compared to the target, our only output is the bad guy’s momentum.

We can then solve for the bad guy’s final velocity v3:

v3 = (m1 * v1) / m2

The initial momentum, based on a muzzle velocity of 1,500 feet per second, and a bullet mass of 0.00066 slugs has the momentum of 0.99 slug-feet per second.

After the bullet strikes its target, the momentum remains the same – we simply divide the initial momentum by the mass of the target, yielding a resulting velocity of about 0.2 feet per second ( about 2.2 inches per second ).

We can see that a typical bullet just doesn’t have enough energy to “throw someone backward”.

Let’s compare to a large bullet, like the .50 AE, with a bullet weight of 300 grains and a muzzle velocity of 1,550 fps.  The momentum is 2 slug-feet per second, resulting in a change in velocity for the target of 0.41 feet per second ( about 5 inches per second ).  Although this much heavier bullet will hit the villain much harder, and maybe knock him back a little, he’s not going to “fly across the room”.

The 12 gauge .00 (“double aught”) buckshot round is about the most powerful civilian-available cartridge.  In a standard load, eight .33 caliber pellets, each weigh about 54 grains, for a total shot load of about 430 grains, with a muzzle velocity of about 1,300 fps, for a total momentum of about 2.5 slug-feet per second, resulting in a change to the target’s velocity of about 0.5 fps (about 6 inches per second).  Although this is definitely a hard hit, and will definitely push someone backward, even a 12 gauge shell won’t cause them to fly across the room.

 

Myth:  Glock Pistols are Porcelain or Plastic

In Die Hard 2, John Mclain claims that the terrorist was armed with a fictional gun capable of being passed through security, undetected:

John McClane: That punk pulled a Glock 7 on me. You know what that is? It’s a porcelain gun made in Germany. Dosen’t show up on your airport X-ray machines, here, and it cost more than you make in a month.

There are some problems with these statements:

• There is no “Glock 7”.  At the time, Glock pistols were brand-new to the US market, but the first production Glock pistol was the Glock 17.
• Glocks are not porcelain nor plastic.  Glocks have a special reinforced polymer frame, and was one of the first pistols on the US market to have one.  However, the barrel, slide, recoil spring, and trigger assembly are all made of steel.
• Glock headquarters is in Austria, not Germany.  The Austrians are the same folks who brought us the Steyr Aug, another innovative gun, which was used prominently by the terrorists in Die Hard 1.
• Having a porcelain gun wouldn’t help you get through an X-ray machine.  It would help you get through a metal detector.  Even a plastic or polymer gun would show up on an X-ray.
• You can’t sneak a Glock through a metal detector.  Even disassembled, the polymer frame of a Glock, per US law, has a steel frame insert that’s guaranteed to trigger a metal detector.  As stated, the barrel, slide, recoil spring, and trigger assembly are all steel.  Even the plastic magazines have a steel liner.
• Although new to the market at the time of the movie, the Glock 17 wasn’t that expensive.  As a matter of fact, just the opposite:  If you could find one, you could be the proud owner of a brand-new Glock 17 for about $400, compared to $500 commanded by Beretta or Smith & Wesson, or $600 for a similar Colt pistol.

 

Polymer Composite, not Plastic

We are quick to point out that the Glock’s frame is NOT plastic.  Rather, it’s a polymer composite.

What’s the difference?

Plastic is one type of polymer.  Although some plastics can be durable or rigid, they can’t stand up to the heat and forces involved in repeatedly firing a gun, without rapidly deforming, melting, or simply shattering.

Although NOT used by Glock, DuPont’s Zytel is an example of a polymer composite, made from Nylon (a type of plastic), resin (a very strong glue), and fiberglass strands.

Zytel is often used for gun parts, such as magazines, handles, pistol grips, hand guards, and parts of the stock, because it’s waterproof, abrasion-resistant, wear-resistant, heat-resistant, structurally very strong, yet it flexes instead of shattering under extreme force.

The formulation of Glock’s polymer frame is proprietary, but it’s clearly much more than a simple plastic.

 

Glock:  The Safest Gun

When they were first made available to the American market, Glocks were highly-criticized for three things:

• Glocks don’t have an external, manual safety.  Many gun pundits claimed that this somehow made the Glock “unsafe to carry”.  This is patently untrue.
• Glocks don’t employ a hammer, and many gun pundits criticized the Glock for being “Double Action Only” (DAO), and therefore inaccurate.  This, also, is patently untrue.
• Glocks have a “plastic” frame, and are therefore not durable nor reliable.  This, too, is patently untrue (as we’ve already seen)

Here is the firing sequence of a Glock pistol:

1. The shooter aims the gun, and inserts his finger in to the trigger guard.
2. The shooter pulls back on a tiny lever at the tip of the trigger, called the “trigger safety”, releasing the trigger, which is normally locked in place.
3. Glocks don’t employ a firing pin, they employ a striker, which is a thicker, heavier piece of metal designed to fire a cartridge without the use of a hammer.
4. As the trigger is pulled backward, the striker safety is disengaged, freeing the striker to move within its channel.
5. At the end of its travel, the trigger bar releases the spring-loaded striker, firing a round.
6. As the slide cycles, the striker is charged and blocked by the trigger bar, and the striker block reengages.

Glock calls this system “Safe Action”:

• The trigger safety prevents the trigger from being actuated accidentally.  Glock recommends a holster that completely blocks the trigger, so that the gun can be safely carried while chambered.
• Both the trigger safety and the trigger must be pulled in order to disengage the striker block.
• The striker can not be released, except by the trigger bar, which only releases the striker when the trigger is pulled completely rearward.

 

Glock: Superior in Torture Tests

When first released to the American market, skeptical gun writers proceeded to put the Glock 17 through a series of durability and reliability tests, unlike anything performed on any other handgun in history.

Here are some of the torture tests:

• Using a fully-loaded, chambered Glock as a hammer, to hammer a nail in to wood.  NOT RECOMMENDED.  But, the nail went in, the Glock didn’t go off.
• Run over multiple times by a sport-utility vehicle.  The writer in question picked up the fully-loaded Glock, chambered it, and fired every round in the magazine, without a misfire.
• Buried in sand and water for up to two months.  The Glock in question was chambered and fully-loaded.  When the writer unburied it, he was able to pop off all 17 shots without a jam, and without even a courtesy rinse-off beforehand.
• Cheap ammo.  All cartridges have a specification, and all guns are designed around their cartridge specification.  That said, many automatic guns are known to have a preference for a certain type or brand of ammunition, that cycles more reliably.  Gun pundits put all sorts of crappy ammunition through the Glock, and it chambered and fired more reliably than its competitors.

I’m fond of saying:  If you have to bet your life on ONE GUN, make it a Glock.

 

Conclusion

Movies and television are a great source of gun myths.  Guns are a pure expression of physics, often referred to as a “remote controlled drill”.  Guns have limitations, just like all machines.  Hopefully, this article has provided clarification about what is or is not realistic.

Thanks for reading, and please look for part 2, which will be published shortly.