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Feb 07 2011

Pique the Geek 20110206: Firearms 101

For good, for ill, or for neither, firearms are an integral part of American life.  Everyone knows in a general sense what guns are, but not so many know much more than that.  The conventional wisdom is that those of us on the left are less familiar with firearms than those on the right (a premise with which I do not agree), but the fact is that it important to have a basic understanding of how firearms work.

At the most basic, a firearm is a device used to deliver a projectile, usually at a high rate of speed, towards some sort of target using chemical propellants that are NOT carried onboard the projectile.  Firearms have evolved over the centuries from quite crude affairs to the highly sophisticated devices that are available currently.

Before we start, please allow me to apologize for the trouble that I had with posting and with comments on Popular Culture Friday evening.  I had multiple freeze ups and extremely slow computer problems overall.  I spent most of yesterday running an arsenal of anti malware tools and system performance enhancers, and it looks like I am back in good shape now.

We shall limit our discussion to modern firearms, except to illustrate particular points.  In my definition, a modern firearm is one that utilizes a series of springs and levers to cause a cartridge to activate, and that has some method of accurately, more of less, directing the projectile of the cartridge towards the intended target.  Most all modern firearms are breech loaders, meaning that the cartridges are introduced from the rear of the barrel.  This is direct opposition to muzzle loaders, where the cartridge (if one is even used) is introduced into the front of the barrel.

In a modern firearm, the cartridge is introduced into the receiver, either by hand, one at a time, or from a magazine (sometimes called a clip, if is a removable magazine) that bypasses the manual operation, allowing much more rapid rates of fire.  Breech loading also allows for much more rapid rates of fire, because to load from the muzzle it is necessary to load the firearm through the path that the projectile has to take when it is fired.  The receiver in modern firearms is designed to withstand the extreme pressures exerted when the cartridge is activated.

In modern firearms, except for some exotic military types, a firing pin is used to activate the propellant in the cartridge.  The firing pin is a piece of metal, often a rather blunt point (usually a flat piece for rimfire ammunition) that causes an impact-sensitive chemical composition to ignite.  This material is contained in the primer, a removable, thin metallic case (for centerfire ammunition) with a thin, burnable membrane on the interior side.  For rimfire ammunition, the priming composition is contained in the rear of the cartridge itself, and since it is not removable, rimfire ammunition can not be reloaded.

This priming composition, when ignited, in turn ignites the main propellant charge.  The extreme pressure developed by the propellant creates a force on the projectile (also called a bullet, if it is a single, solid piece), forcing it down the barrel and out the muzzle.  By the way, NEVER call an entire cartridge a bullet.  Only the piece that flies out the muzzle is the bullet, and some firearms do not even fire bullets, but rather lots of small spheres, called shot, hence the term shotgun.

Except for shotguns and illicitly devised zip guns, the interior of the barrels are invariably rifled, hence the term rifle, although pistols also have rifling.  Rifling is a series of helical grooves (the part of the barrel cut away during rifling, and lands, the part of the barrel that is left in place.  Long guns that are not rifled, except for shotguns, are called muskets.  The reason to go to all of this trouble has to do with accuracy.  A projectile shot from a smoothbore exits the muzzle with very little spin.  Imparting spin on the projectile improves accuracy by a huge factor.

Here is a sports analogy that some might find useful.  In baseball, there is a pitch called a knucleball wherein the pitcher releases the ball in such a manner that little if any spin is imparted to the ball.  Because of atmospheric interactions, a knucleball does not travel in a straight line, but weaves left and right and to an extent up and down.  In contrast, when a football is passed, a nice spiral imparts stability to the ball in motion.  Not that in some football kicks the ball does not spin, and has an erratic pathway.  The same factors apply to bullets.  In a vacuum the spin is much less important, since there is no atmosphere with which to interact.

Shotguns are not rifled because of several reasons.  First, they are intended for much shorter ranges than are rifles (ranges of over 100 yards are just about unheard of for shotgun targets, but depending on the specifics, rifles are good for up thousands of yards).  Second, except for rifled slugs, shotgun ammunition consists of the casing, primer, and propellant, but instead of a single projectile there are from a few to hundreds of individual pellets, and these spread out with distance.  Thus, it is possible to hit a target with at least a few pellets even if the shooter’s aim is not perfect, while a single bullet would miss.  By the way, rifled slugs are single projectiles with the rifling molded into the projectile itself, so it gets some spin stabilization even though the bore is smooth.  They are used for larger game, while the smaller pellets are used for small game and birds.

Let us look at some elementary ballistics.  Neglecting atmospheric interactions, all objects fall at the same rate.  There is a school demonstration where you put a coin and a feather in a chamber and release them with a remote catch.  The coin falls rapidly, while the feather sort of floats down.  After resetting the coin and the feather, you use a vacuum pump to remove the air from the system.  When the catch is released, the coin and the feather hit the bottom at the same time.  Bullets are dense enough so that ate atmosphere does not significantly affect the rate of their fall, 9.8 meters per second per second, or the acceleration due to gravity.  Keep this in mind for just a bit later.

All objects that do not have internal means of locomotion will, when ejected, travel in a parabolic path.  This is true for rocks, cats, bullets, birds (if they are quite dead), and anything that does not have a huge interaction with the atmosphere, like a sheet of paper or a feather.  This path does not hold for birds (if they are not dead), bats (unless they are the baseball kind), aeroplanes, and rockets.  Since the acceleration due to gravity is the same regardless of mass, all bullets, if fired exactly horizontally every time, hit the ground after the same amount of time.  As a matter of fact, if you could somehow devise a method to drop a bullet horizontally at the exact instant a bullet fired from a rifle exited the muzzle, both bullets would hit the ground at the same time, assuming the ground is completely level.  At first that does not seem to make sense, but it is exactly right.

Let us imagine that we are firing a rifle that is in a fixture to keep it exactly level every time.  We have three dimensions, and let us define the x-axis as the direction of the rifle barrel, the y-axis as left and right, and the z-axis as vertical.  Since we have spin stabilization, the y-axis is not important (unless there is a significant wind).  Let us also say that it takes 2.00 seconds for a bullet dropped vertically at muzzle height to reach the ground.  Since in the vector analysis the x component has nothing to do with the z component, the bullet from the rifle also takes 2.00 seconds to reach the ground.  Neglecting air resistance, the only factor that determines the maximum range of the bullet is the muzzle velocity.  In fact air resistance is not vanishingly small, and reduces the actual range of the bullet fired because it continuously travels more and more slowly in the x direction, but still falling in the z direction with an acceleration of 9.8 m/s/s, since air resistance is negligible in the slow z direction.  Thus, the parabolic track of the bullet determines at what range it hits the ground.

If you think of it for a minute, the faster that the bullet exits the muzzle, the further it will travel before it hits the ground.  The curvature of this path is called the trajectory of the bullet, and is a function for mostly the muzzle velocity and to a smaller degree the shape of the bullet.  Bullets with a more aerodynamically favorable shape will travel further, since they do not have a much drag as, say, a round ball.

There is another way to increase range, and that is to set the rifle at an angle so that some of the energy of the propellant is used to increase the maximum elevation of the bullet, so that it has further to fall than if fired exactly horizontally.  The time required to reach maximum elevation and the longer time to reach the ground from that elevation makes the bullet carry further.  Neglecting atmospheric interactions, a 45 degree angle gives the maximum range.  Now, it is really hard to hit a target if you are aiming at a 45 degree angle, so small arms do not often use such radical elevations, but military artillery certainly does.

When a shooter sights in a rifle, a specific range is chosen, say 200 yards and the sight adjusted such that the bullet hits the bull’s eye.  Actually, what is happening is that the sights are set so that at that range, for that particular combination of rifle, cartridge configuration, and shooter it appears to the shooter that the trajectory is “flat”.  In reality, the sights are set so that the muzzle is pointed up just a little to compensate for the z direction falling of the bullet.  When sighted in for 200 yards, closer targets will have hits that are high, and further ones hits that are low.  Good shots compensate for that with a little practice, and some sights have adjustments that can be used to assist.

For big game hunting (deer and larger), it is helpful to have a rifle with a relatively “flat” trajectory, because in open country a wide diversity of ranges are apt to be encountered.  That usually means a relatively small bullet with a very high muzzle velocity, so that it travels further before the bullet falls so much.  For heavily wooded areas, a heavy, slow bullet is ofter preferred because the range is not apt to be too far and the heavier, slower bullets are affected less by twigs and leaves than are the lighter, faster ones.  Next week we shall get into the physics of different kinds of loads.

Rifles can be single shot, where the shooter has to load a new cartridge manually after each shot, repeating rifles where a lever is used to eject the spent round from the receiver and insert a new one from either an external or internal magazine, bolt action where a different configuration is to eject and load, or semiautomatic, where either energy from the recoil of the rifle or gas pressure from combustion of the propellant causes the spent round to be ejected and a new one loaded without human intervention.  All that the shooter has to do is pull the trigger and the weapon fires again, and as long as there is ammunition in the magazine will continue to do so.

Fully automatic weapons are like semiautomatic ones except that a new pull of the trigger is not needed to keep firing.  As long as the trigger is kept in the fire position, the rifle reloads and shoots until either the trigger is released or the magazine is depleted.  By the way, it is NOT illegal under Federal law to own fully automatic rifles if certain requirements are met.  Obviously there are legal issues, just like in all weapons, so felons, the mentally ill, and other disqualifying factors are involved.  In addition, the buyer has to pay Treasury a very high transfer fee for the rifle to change hands.  These weapons require special licenses for both the owner and the weapon itself, and if you get caught without the paperwork for either yourself or the particular weapon you have a LOT of explaining to do.  There are some commercial outfits that offer to the public on a fee basis the chance to shoot fully automatic weapons, because there are not any restrictions on shooting the weapons (felons and the otherwise disqualified being exceptions), but on owning them.

In interesting factor in the law that makes it legal to own fully automatic weapons is that they and any spare parts have to have been manufactured before whatever date the law restricting ownership came into effect.  Thus, all legal (for individuals, police and certain security outfits have different requirements) fully automatic rifles were manufactured before sometime in the early 1930s.  If you break a spring in a magazine, you are out of luck unless you can find another old magazine that is being “parted out” or a working old one.  I believe that the logic for this clause has to do with depriving people of property without due process.  Thus, if you had a machine gun that was legal before the law took effect, you could register it with Treasury and still be OK.  I believe, but am not positive, that there is an annual fee in addition to the transfer fee.  If anyone knows for sure please post a comment.

Next week we shall get into some of the physics and a little of the chemistry behind firearms, and after that we shall find a new topic.  Suggestions are always welcome.

Well, you have done it again!  You have wasted many more einsteins of perfectly good photons reading this piece that is not worth shooting.  Usually I make a joke about some contemporary right wing figure, but, seeing how this the centennial of Ronald Wilson Reagan’s birth, decided to say something nice about him.  As far as I can tell, he was at least as good an actor as Bonzo was.  I do, however, always learn much more than I could possibly hope to teach by writing this series, so please keep those comments, questions, corrections, and other feedback coming.  I shall stick around as long as comments are coming or until I wear out, and shall return tomorrow evening at 9:00 PM Easter, give or take, for Review Time.

Warmest regards,

Doc

Crossposted at Antemedius.com, DAilykos.com, and at Docudharma.com

11 comments

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  1. Translator, aka Dr. David W. Smith

    rying to stay on target?

    Warmest regards,

    Doc

  2. BobbyK

    I’ve learned quite a bit from your post.  

    My experience with guns begins and ends with a 1938 .177 caliber Daisy Red Ryder Carbine that’s been in the family since… I guess 1938 although that would have made my father 3 years old when he got it.  I’ll have to ask him about that.  

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