Tuesday, November 23, 2010

Pistols: Basics

While we've discussed several firearm topics in this blog, one major omission so far has been on the topic of pistols. So we will study these in the following posts.

A pistol is a class of firearm that falls under the category of "handgun" (i.e.) weapons that are small enough to be fired with one hand. While revolvers also fall under the category of "handgun", the main difference between pistols and revolvers is that pistols have a chamber that is part of the barrel, whereas revolvers have multiple chambers that rotate about an axis. Pistols are actually an older class of weapon than revolvers, in fact, the first pistols were made in the 1500s, whereas revolver designs didn't appear until the 1800s. In fact, the early revolver class weapons, such as the pepperbox were originally called "pepperbox pistols" and it was only in the mid 1800s that the term "revolver" came into use, to distinguish it from "pistol".

The earliest pistols were developed in the 1500s, for use at close ranges and by mounted horsemen. The term is believed to be from the Czech word "pistole" which refers to a small flute or pipe, or from Pistoia, a town close to Florence, Italy, where some of the early pistols were made. Allegedly, the first inventor was a citizen of this town, one Caminellio Vitelli, who made several pistolese (Italian for "from Pistoia"). In those early days, the term pistolese was interchangeably used for both firearms and small daggers.

The first pistols were single-shot weapons. In effect, the user simply held a burning match cord to the touch hole of firearm to set it off. In other words, they were merely portable cannons.

Later pistols used a variety of firing mechanisms: matchlock, wheel-lock, snaphaunce, flintlock, percussion caps and finally, the modern cartridge. The example in the image above is an early German made pistol from about 1515 or so. It has a file lock, where a rough piece of serrated steel is dragged over a flint, which drops sparks into the firing pan, which then lights and discharges the weapon.

In the following posts, we will study pistols throughout history.

Thursday, November 18, 2010

What is the difference between a rifle, SLR, submachine gun, carbine etc.?

A very common question among newbies to firearms history is "What is the difference between a rifle, a sub machine gun, a machine gun, a carbine, SLR, assault rifle etc." This post attempts to point out the differences and name famous weapons of each type.

Rifle: The name "rifle" originally comes from the fact that the barrel of such weapons is "rifled". This means that the barrel has grooves in it to impart spin to the bullet as it comes out of the barrel. This spin helps to stabilize the bullet as it travels through the air and gives it a predictable drift (e.g.) a particular rifle may fire bullets that travel 1-2 cm. to the right every 100 meters on a windless day. This feature allows the user to reasonably predict where a bullet will hit and gives the rifle its accuracy. Earlier firearms, such as muskets, had smooth barrels. Smooth bore weapons were much easier to manufacture than rifles, but lacked in accuracy, as the bullets didn't have stability in the air and deviated in a random direction from the intended target. Therefore, the standard strategy for European armies of that period was to line up men in parallel lines and tell them to all simultaneously open fire at the enemy, because almost no one could reliably hit the enemy that he was actually aiming for. This massed fire strategy worked because some enemy would be hit, even if they weren't the ones that were originally targeted. These days, most modern firearms, even small ones, such as revolvers and pistols, have rifled barrels. Therefore, in modern times, the word "rifle" by itself, implies a firearm that has a rifled barrel, is designed to be fired from the shoulder, is manually fed (i.e. after each shot fired, the user has to manually operate a lever to feed a new cartridge into the weapon) and carries a small number of cartridges internally (say 1 to 5 cartridges). Examples of modern rifles from the early 20th century would be the famous American .30-06 M1903 rifle, the British 0.303 Lee-Enfield, the Mauser M98 etc.

Assault Rifle: In the early part of the 20th century, it was realized by some military forces that most conscripted troops, who were hastily trained in wartime conditions, had less than a 50% chance of hitting a target beyond 300 meters. It was also realized that most infantry encounters occurred at less than 500 meters and rate of firepower was also an important factor in these encounters. It was therefore reasoned that there was no need to give such soldiers a weapon and ammunition capable of hitting targets at 2000+ meter ranges, since most soldiers could not hope to hit a target that far away in the first place. Instead, it was reasoned that it was better to give troops lesser powered (and therefore, smaller and lighter) ammunition to suit the actual ranges that most infantry engagements occurred at and a correspondingly lighter weapon suited to fire this ammunition. With lighter ammunition and weapon, the soldier could carry more ammunition and therefore use a weapon with a higher rate of fire. While the concept was around before World War II, it was the German StG 44 (Sturmgewehr 44) that really popularized the concept. The word Sturmgewehr was coined by Adolf Hitler and literally translates to "Storm Rifle" (the word "storm" being used in the context of "storming a castle" or "assaulting a castle") and the term "assault rifle" is actually a translation of "Sturmgewehr". Even though there were earlier weapons that could be classified as assault rifles, many historians consider the StG 44 as the first to form the concept of modern assault rifles. In these times, an assault rifle is a weapon with the following characteristics:
  • Has a rifled barrel (as in the case of the rifle described in the previous section).
  • Has provision to be fired from the shoulder, just like a rifle.
  • Uses an intermediate powered cartridge. This means that the cartridges are smaller than those used by a regular rifle, but larger than the cartridges used by a pistol. This is one of the key differences between an assault rifle and a regular rifle.
  • Is capable of selective fire modes. This means it allows the user to select between firing different numbers of shots each time the trigger is pulled. In semi automatic mode, the weapon will shoot one bullet each time the trigger is pulled. The weapon automatically chambers the next cartridge to fire, but the user needs to let go of the trigger and pull it again to shoot it. In burst mode, the weapon will fire a preset number of cartridges (say 2 or 3) with each trigger pull. In fully automatic mode, the weapon will continue to keep firing as long as the trigger is pulled and there is ammunition. The ability to switch between various modes of fire is a key feature that distinguishes an assault rifle from other types.
  • Has a detachable magazine. Most modern assault rifle magazines carry 20 to 30 cartridges or so.
Examples of assault rifles include the AK-47 family, the M16 family etc.

SLR: This is an acronym for "Self Loading Rifle". The term "SLR" is usually used in commonwealth countries. This has some common features with the assault rifle described above. Like the assault rifle, this is also a weapon that has a rifled barrel and is designed to be fired from the shoulder. It also uses an intermediate powered cartridge and has a detachable magazine like the assault rifle concept. The one key difference between assault rifles and SLRs is that SLRs have only one firing mode, the "semi-automatic mode". This means that each time the user pulls the trigger, the weapon will fire only one cartridge. It will automatically eject the fired cartridge, load the next cartridge and prepare the weapon to fire, but the user has to let go of the trigger and then pull it again to fire the next cartridge. This is unlike an assault rifle, which has multiple firing modes and allows the user to switch between them. Examples of SLRs would be weapons like the American AR-15 and the Indian Ishapore 1A1 SLR. The AR-15 is a semi-automatic version of the M16 rifle and the 1A1 is a semi-automatic version of the Belgian FN FAL assault rifle.

Carbine: This is a term used for weapons that are versions of rifles or assault rifles, but with a shorter barrel and lighter weight. Carbines are bigger than pistols, but smaller versions of rifles. In the days of the Wild West, mounted riders preferred a shorter and lighter firearm because these were easier to operate than full sized firearms, when riding. In more modern times, people inside moving vehicles or in close quarter jungle combat, preferred shorter weapons for the same reason. Since carbines have shorter barrels, they lack in accuracy compared to full sized rifles or assault rifles. While they use the same cartridge as their full sized cousins, the shorter barrel also means reduced velocity bullets. Many assault rifles also come in a carbine version. For example, the American M4 (a carbine version of the M16 assault rifle), the Israeli Galil SAR (a carbine version of the Galil assault rifle), Steyr AUG carbine ( based on Steyr AUG assault rifle. The carbine form uses a 16 inch barrel, whereas the assault rifle uses a 20 inch barrel) etc.

Submachine Gun: This is a weapon that shares some similarities with assault rifles, but one key difference is that submachine guns are designed to fire pistol cartridges instead of intermediate cartridges. As a result of this, submachine guns are generally lighter and smaller than assault rifles and are about the same dimensions or smaller than carbines. Since they use pistol ammunition, they also have less recoil and therefore can be fired from either the shoulder, the hip, or even holding it like a pistol. The first weapon to use the term "submachine gun" was the famous Tommy Gun that we studied about earlier. This is a fully automatic weapon that fires .45 ACP cartridges, the same cartridge used by the Colt M1911 pistol. Another famous submachine gun from the World War II era is the British Sten gun, which is also a fully automatic weapon. Modern submachine guns such as the Heckler and Koch MP-5 are capable of selecting multiple firing modes. Submachine guns are more preferred for close-range combat in urban environments because, with lower powered pistol cartridges, there is less risk of bullets penetrating through walls and hitting innocents on the other side

Machine Gun: This generally denotes a weapon that is capable of rapid, fully automatic fire and carries a large supply of ammunition. Fully automatic fire means that the weapon will keep firing as long as the trigger is pulled and there is a supply of ammunition available to it. Most machine guns fire either full sized or intermediate sized ammunition, similar to rifles and assault rifles. Machine guns generally carry a large supply of ammunition in ammunition belts, drum magazines or box magazines. This means that they generally have hundreds of cartridges available to them, unlike the 20-30 cartridge magazines used by assault rifles. They are also generally heavier than rifles and assault rifles. Examples of machine guns would be the Gatling Gun, the Gardner Gun, the Bira gun etc. Modern machine guns include the Browning Automatic Rifle (BAR), the British Bren gun, the American Stoner 63, the Belgian FN Minimi etc.

Tuesday, November 16, 2010

Shooting: Compensators and Muzzle Brakes

When shooting a firearm, one may notice that there is a tendency for the muzzle to rise up in the air after the shot is fired. This effect is called muzzle climb or muzzle rise. The cause of this is basic physics. Look at the two images below:

When a firearm is discharged, there are multiple forces acting upon it. The gases generated by the burning propellant of the cartridge, pushes the bullet out the barrel and also pushes back on the firearm. This force acts on the centerline axis of the barrel. Let this force be represented by A in the two diagrams above. Now, the user of the firearm is also resisting the kick, by holding the firearm with his hands. Let these forces be represented by B in the diagrams above. Note that for the assault rifle, there are two points where force B acts upon (i.e.) at the stock and at the grip. Also note that in both diagrams, force A is acting at a higher point than force B. This causes the rotational torque C, which causes the front of the firearm to rise.

This effect is more visible for heavier caliber weapons or when multiple shots are fired rapidly. There must be some way to prevent this muzzle climb for happening, because no one wants their weapon to act as though it is on anti-aircraft duty, when they're trying to shoot at a target on the ground!

One way to reduce this effect is if A and B are in the same axis (or fairly close to the same height), then the torque C is minimized. Another way to reduce this is to use devices such as a compensator or a muzzle brake.

Public domain image. Click on image to enlarge

In the above picture, we observe that the gentleman in the front of the picture is firing an AKM assault rifle. Notice that the tip of the barrel has a slanted tip and is slightly tilted to the right as well (it is more visible in the enlarged image). This slanted tip is not due to wear and tear or poor maintenance of the weapon -- it is actually a feature. That device is called a slant compensator. What it does is direct some of the escaping gases upwards, thereby pushing the muzzle down. This counteracts the torque trying to push the muzzle up and thereby makes it easier to keep the weapon pointed at the target. The AKM also has a tendency to move to the right, which is why the compensator is also slightly tilted that way, so that it pushes the muzzle to the left to counteract that movement as well. When the Russians decided to make an improved AK-47 version (the AKM), this was one of the standard features added to the AKM model. This simple device could also be retrofitted to older AK-47 models, simply by screwing on this device to the tip of the barrel.

Another device that is similar is called a muzzle brake. Basically, this consists of a small tube that has a number of perforations along its sides, which is attached to the end of the muzzle. These perforations allow the gases to escape at an angle to the muzzle, which not only helps reduce the muzzle climb, but also reduces the recoil felt at the back of the weapon.

Muzzle brake at the tip of an M16 assault rifle.

Yet another way to reduce recoil is called porting. Basically, this involves drilling precise holes near the end of the barrel, which allows some of the gases behind the bullet to escape upwards as the bullet is exiting the barrel, thereby pushing the barrel down.

Public domain image. Springfield Armory XD-40 pistol with ported barrel.

The advantage of such devices is that they reduce muzzle climb as well as felt recoil. This improves the accuracy of the user. It also reduces the load felt by the user during long shooting sessions.

There are also a few disadvantages of such devices. One is that the noise level of the weapon increases by a few decibels. They also increase the flash seen at the end of the barrel. Some muzzle brakes redirect some of the gases towards the user to reduce recoil, but this could cause some of the pressure wave to be redirected to the user as well as extra noise and flash, thereby causing some discomfort. Additionally, if the shooter is firing from a prone position, the redirected gases could throw up some extra dust towards the shooter, which could impair visibility and give away the user's position. Finally, the extra weight at the tip could affect the overall balance and handling of the weapon.

Saturday, November 13, 2010

Sights: Zeroing a sight

In the last few posts, we've studied various types of sights. Irrespective of the type of sight used, it must be adjusted so that it points to the spot where the bullet will impact when the trigger is pulled. Such an operation is called "zeroing". We will now study how to zero a weapon.

There are quite a few issues to consider when zeroing a weapon. We will study these first.

The first issue that must be realized is that a bullet fired from a firearm doesn't travel in a straight line. Instead, it travels in an arc and also drifts to one side. We discussed why this happens and also defined two terms called windage and elevation during our study of sight basics. Therefore, if a bullet strikes exactly the point we're aiming through the sights, from a distance of (say) 50 meters, it will definitely not strike the point that we're aiming at, from a distance of 100 meters (assuming the sights aren't adjusted for elevation and windage) because of the way the bullet moves. Hence, when we say that a firearm is zeroed, there must be a reference distance to the target, at which the sights are zeroed. Since different weapons have different shooting ranges, the reference zeroing distance depends on the type of weapon and the ranges it is typically expected to be used. For instance, pistols may be zeroed at 15 meters or 25 meter range, but an M16 rifle is typically zeroed at 200 or 300 meter range. Even though most pistols can be fired beyond 25 meters and the M16 can shoot well beyond 300 meters, the reference zeroing distance is the distance at which it is typically expected to be used under most conditions.

The second issue is to note is that different manufacturers of cartridges may make propellants which produce different amounts of energy and the profiles and weights of the bullets may be slightly different from manufacturer to manufacturer. These could also affect the path of travel of the bullet. Hence, when the firearm is zeroed, it is normally zeroed with the type and brand of ammunition that it is most expected to be used with.

The third issue that affects where the bullet strikes is based on the individual and the angle that he/she holds their head and peers through the sights, when aiming the weapon. For instance, many rifle shooters place their head so that the tip of their nose barely touches the rifle stock. Since different individuals have different shaped heads, therefore a weapon that has been zeroed for one individual will not necessarily strike the same point if another person is aiming the weapon.

The fourth issue is that as there is wear and tear in the firearm, it may shoot differently after some use, due to wear of the rifling, chamber etc. Rough usage may also misalign the sights. Hence, all weapons will need to reset their zero after some use.

With that said, we will discuss a procedure to zero the iron sights of an M16 rifle (or its civilian variant, the AR-15). The same basic principles can be used for zeroing any type of pistol or rifle for any type of sight.

For an M16 or AR-15, the US Army and US Marine Corps advocate the reference distance for zeroing the rifle to be 300 meters. The actual procedure is done at 25 meters though, using a target that has everything scaled by 1/12th actual size.

The M16 has aperture type iron sights, which we studied about previously. Both the front and rear sights are adjusted in discrete incremental amounts. Each time they are adjusted by one increment, a click sound is heard. Hence, adjustments are specified in number of click steps.

Initially, the user adjusts the sights so that the rear sight is using the larger aperture hole (the 0-2 aperture) and turns the windage knob so that the windage indicator is centered about the windage scale, as shown in the image below. The elevation knob in the rear sight is then set to the 8/3 setting (300 meter setting mark. We will discuss why this setting is labelled "8/3" at the end of this article.) and then clicked one click clockwise past it initially. This rear elevation knob will not be touched again until the adjustments are completed.

Next, the front sight post is adjusted. Note that the front sight is mounted on a flat disc with four notches cut on its edge. There is a spring loaded detent that enters one of these notches and locks the sight in place. To lower or raise the front sight post, one must depress the detent with a special tool (or a sharp object, such as a nail or a bullet tip) and then rotate the sight post clockwise or counterclockwise as needed. Each rotation of 90 degrees produces one click. The front sight is raised or lowered until the base of the front sight post is flush with the front sight well.

At this point, the rifle is said to be set at "mechanical zero" initially.

Next, the weapon is taken to the range and placed on a firm base, such as a bench rest. In the case of an M16, there is a special zeroing target sheet that can be placed at 25 meter distance away from the rifle. The target sheet is appropriately scaled to simulate a target at 300 meter range. The zeroing target sheet is shown below:

The target sheet has a black silhouette with a circle in it. This is the part that the user is supposed to shoot at. There are also eight circles around the black silhouette, each one topped with an arc with an arrow head on one side of the arc. These eight circles indicate which sight to adjust (front elevation or rear windage knob) and the arrows indicate the direction to turn the sight adjustment (clockwise or anticlockwise) to adjust the shot towards the center of the target. Notice that there is also a grid in the target sheet and there are numbers that are on the edge of the grid. These numbers tell the user how many clicks to turn the front sight elevation or rear sight windage knobs. The numbers on the X axis are for how many clicks to turn the rear sight windage knob and on the Y axis are for how many clicks to turn the front sight. On an M16, turning the front elevation sight by one click moves the impact point of the bullet up or down by one grid square. Turning the rear windage knob by three clicks moves the impact point of the bullet by one grid square left or right.

The user initially mounts the rifle on a bench rest (or tries to get as stable a shooting position as possible, using a prone shooting position, sandbags for support etc.) and aims for the center of the black silhouette and fires 3 shots. The user then walks up to the target and examines it and sees where the three bullet holes are and determines their average center. The user then looks at the grid and determines which sights to adjust and how many clicks to adjust them by. Let's say the bullets impacted 5 squares to the right and 2 squares down from the center of the target. Then the user knows from the grid markings that he has to adjust the front elevation sight by 2 clicks clockwise and rear windage knob by 15 clicks anticlockwise. Then the user walks back to the bench rest, turns the sight adjustment knobs appropriately and then shoots 3 more times. Then the user walks back and examines the three new holes and sees if they are hitting the center of the silhouette now. If not, the user again looks at the edge of the grid and determines which sights to adjust and by how much and repeats the procedure until the center of the silhouette is hit to the user's satisfaction.

Now the user turns the rear elevation knob in the rear sight one click counterclockwise, back to the 8/3 setting (the 300 meter setting mark. Remember that it was turned one click clockwise past the 8/3 setting initially). At this point, the rifle is fully zeroed at 300 meter range. To shoot at different ranges, the user now merely needs to turn the rear elevation knob to the appropriate range setting.

The following video shows how the procedure is done:

Of course, this procedure simulates the 300 meter range by using a scaled target at 25 meters. Hence, any small deviation at 25 meters may become more prominent at 300 meters. Therefore, some precision shooters adjust their sights as above, but then take their weapon out to an actual 300 meter range and test to make sure it shoots correctly there also and make minute adjustment changes as needed. Then they set the rear elevation knob to different range settings, such as 400 meters, 500 meters etc. and fine tune the settings appropriately. This way, any small errors will be minimized at longer ranges and negligible at shorter ranges.

Incidentally, this might be a good place to explain why the M16 rear elevation control says "8/3" for the 300 meter setting. If you look at that knob, its minimum setting corresponds to the "8/3" mark. The 3 means the setting for shooting at 0-300 meter range. Now, if the knob is turned 3 clicks, the next visible digit is 4, which is for shooting at approx. 400 meter range. Three more clicks brings the next digit 5 for shooting at approx. 500 meter ranges, the next digit is 6 for 600 meters, the next is 7 for 700 meters and then when the knob is turned further, it completes one full rotation and comes back to the "8/3" setting, which is now the setting for the 800 meter mark, the max. elevation setting on the M16A2. This explains why that mark is labelled "8/3". On M4 rifles, the corresponding knob is labelled "6/3" because the max. elevation setting on an M4 is for 600 meter range.

Since accuracy is affected by wear and tear, temperature, vibration and shock, rough usage (i.e. the sights get knocked out of alignment) etc., it is necessary to re-zero the weapon periodically. How often this is done depends on the user, or organization procedures. For example, different branches of military forces have different requirements on how often to zero weapons.

Friday, November 12, 2010

Sights: Reflex Sight

In the last post, we studied some details about laser sights. The next type of sight that we will study in this post is called the reflex sight.

When we studied telescopic sights, we noted that scopes have reticles (crosshairs) etched inside to indicate where the barrel is pointing to. Similarly, one of the key features of all laser sights is that they project light towards the target to show where the weapon's barrel is pointing to. Reflex sights also have reticles, like telescopic sights, but there is one important difference in how the reticle is displayed. Reflex sights feature a beam splitter or a dichroic mirror. The image of the target is combined with a reflected image of a reticle and projects the reticle image on top of the target image. The reflected reticle image can be illuminated if needed, thereby providing a clearer image of the reticle.

Image licensed under the GNU Free Documentation License version 1.2 or later. Original image by user Falcorian at en.wikipedia.org

In the above image, we see a reflex sight with a bright red dot projected on the image. A sight like this uses a small battery to produce the bright red spot and then projects it on to the image. There are several reflex sights like this, such as the Aimpoint series, EOTech etc. The brightness of the red dot can be increased or decreased to match the surrounding light.

One of the more common reflex sights being used these days is the ACOG (Advanced Combat Optical Gunsight) that is used by the US Army and the US Marine Corps. This type of sight is manufactured by Trijicon and comes in a variety of configurations.

Click image to enlarge. Public domain image

Different ACOG models have different magnification powers, different colors and shapes of reticles and some have features to allow for elevation. All ACOG models have an unusual feature for reflex sights in that they don't use batteries for the reticles. Instead, they use fiber optic cords for daytime and tritium lamps for night time conditions. We studied these two devices earlier when we studied how to make iron sights more visible.

Reflex sights can be used under a variety of light situations and allow quick target acquisition. The user can use both eyes to aim, when using a reflex sight. On the other hand, reflex sights add a bit of bulk to the weapon and affect its balance.

Wednesday, November 10, 2010

Sights: Laser Sight

We've spent the last few posts discussing iron sights and telescopic sights. In this post, we will study a new type of sight that is mainly seen with handguns and rifles, the laser sight.

A laser is merely a light source which has the property that the light emitted is focussed as a narrow beam with very little divergence. This is unlike a regular light bulb that emits light in many directions in a variety of frequencies. Due to the property of low divergence of the beam, lasers can be used to indicate the aimed point on a target.

The original laser devices were extremely large and bulky, but due to advancement of semiconductor technology, they can be made much smaller these days. The typical laser sight today is small enough to be mounted to the underside or top of a pistol.

The laser sight is attached so that it is parallel to the barrel. Since a laser beam does not diverge much, the user can move the barrel until the light spot from the laser hits the desired target. The spot indicates the area where the barrel is pointing to. It must be remembered though, that the light travels in a straight line, but real bullets travel in an arc, due to forces of gravity, wind etc. The user may therefore need to allow for windage and elevation depending on the distance between the weapon and the target.

Most laser sights utilize red laser diodes. In the late 1990s, green laser diodes were invented, but it wasn't until 2007 that the first mass produced green laser sight was invented. Green laser sights are a bit more expensive than red laser sights and consume more battery power. However, green laser light is much more visible to human eyes than red laser light, especially in bright daylight conditions.

The two pictures above show a red laser and a green laser during day time and night time. In the bright day time shot, the red laser dot is barely visible in the picture, whereas the green dot is easily seen. The green dot is also seen much more clearly at night time, where the entire beam is clearly visible, not just the dot. With red lasers, only the dot is visible normally and the beam is usually only discernible when the surroundings have smoke or dust. This makes weapons using green lasers much more easier to aim than red laser sights.

One of the disadvantages of red and green laser systems is that the target (and other people surrounding the target) can also see the dot and be aware that he or she is being targeted. Also, the visible beam gives away the position of the person pointing the weapon. Therefore, some systems use an infrared laser that is only visible to people wearing night vision devices. Unless the target is also wearing a night vision device, he or she is not aware of being targeted and doesn't know where the person aiming the weapon is either.

Laser sights allow the user to quickly acquire a target. With other types of sights, the user needs to concentrate on pointing the sights to the target and therefore loses focus of things that are surrounding the target. Laser sights allow the user to not lose details of the target's surroundings. It also allows one to aim the weapon without physically staring down the barrel, which allows for greater concealment.

On the other hand, laser sights need batteries and there is the chance of the batteries running out when they are needed. Red laser beams are hard to see in daylight or in clean surroundings. Green lasers are more visible in bright or clear conditions, but they chew through batteries much more quickly than red lasers and are also more expensive than red lasers. Laser sights also alter the balance of the weapon somewhat and rough usage can change the spot where the laser is pointing, which means it no longer points to where the barrel is pointing.

Tuesday, November 9, 2010

Sights: Telescopic Sight - II

In our previous post, we started our study of telescopic sights. We will continue our discussion of such sights in this post.

In our previous post, we saw how an user can use the scope to estimate the range to a target. Once the range is estimated, the user can adjust for windage and elevation. As a matter of fact, most telescopic sights have controls to adjust for these parameters. Since some scopes have variable magnification, these may have additional controls to zoom the view and adjust for parallax error. Some scopes may offer an illuminated reticle for low light conditions and have an additional knob to adjust the brightness. Some very high end models even come with built in laser range-finders for better accuracy.

Since very few weapons are designed with built-in telescopic sights, most of these are mounted separately. Most western military rifles are designed with a standard picatinny rail on them, to which various accessories (including a telescope) may be mounted.

M4 carbine with scope mounted on picatinny rail on top of the weapon. Click on image to enlarge.

In other weapons, people usually attach a scope base to the rifle and then add scope rings to hold the scope in place on top of the base.

There are some advantages to telescopic sights. In most iron sights (except aperture type iron sights), the user needs to focus on three points simultaneously, which is not easy to do. With a telescopic sight, all the user needs to do is focus the cross hairs of the reticle on to the target. With a magnified view, it allows for shooting at longer ranges. The shooting as well as target identification are more precise as well. They also provide much more accurate windage and elevation measurements than other systems we've studied so far. Most modern high quality scopes are also surprisingly durable and can take a fair bit of punishment.

There are also some disadvantages. The main one is cost. Telescopic sights are way more expensive than iron sights, though the cost has come down in recent years. These sights are also more bulkier than iron sights and definitely alter the balance of the weapon. Thirdly, they cannot withstand bad weather as easily as iron sights. Also, some weapons that eject cartridges from the top (such as lever action rifles) need to have the scope mounted slightly off center, so that it does not interfere with the ejected shells.

On heavy recoiling weapons, the scope rings need to be tightened very consistently, otherwise the scope will go out of alignment.

For a long time, most militaries would only equip snipers with telescopic sights, because of the high cost of a scope. However, as the cost of scopes has fallen in recent times, some militaries have started to equip some regular infantry with scopes as well.

Monday, November 8, 2010

Sights: Telescopic Sight - I





Public domain image. Click to enlarge.



Public domain image. Click image to enlarge.



Above image is licensed under GNU Free Documentation License 1.2 by Kosiarz-PL at wikipedia.org
Public domain image of Schmidt & Bender scope reticle





Public domain image


Public domain image




Saturday, November 6, 2010

Sights: Iron Sights: Improving Visibility of Iron Sights

In the last few posts, we've studied various kinds of iron sights. Now, one of the desired properties of any type of sight, not just an iron sight, is that they should be easy to see, but should not be bright enough to blind the shooter. There are a few ways that this can be ensured. We will study the methods here.

Since sights should not be very shiny and reflective, particularly the front sight, there are a few ways to reduce glare from the sights. First, there are metal treatments such as parkerizing and ferritic nitrocarburizing, which we studied about previously. These treatments not only apply a protective finish to the weapon, but also reduce the reflective glare. Another way to do this would be to simply apply some non-reflective matte finish paint on the sights. Yet another way is to bead blast the sights or cut serrations on the surface to make them less reflective. Finally, some sights have a hood around them to shade the sights and reduce the glare.

However, there is another problem to consider too. The sights should not be dark enough that they merge in with the background. There should be sufficient contrast between the sights and the background, so that they can be picked up much easier. There are several ways to do this as well.

The first method is very simple: the manufacturer simply paints a different color on the front and rear sights to make them stand out more.

In this case, the manufacturer has painted around the square channel of the rear sight with a white paint and painted a white dot on the face of the front sight as well. In other cases, it may just be two dots on the rear sights and one dot on the front sight. Another variant is to put one rear dot in the center of the rear sight and another dot on the front sight. When the sights are lined up correctly, the two dots are aligned vertically, like the digit "8". Another version of this is to have a white vertical line painted in the middle of the rear sight and a dot on the front sight. When the sights are aligned correctly, it looks like a lowercase letter 'i'. Some manufacturers use different colors for the front and rear sights. For example, some people prefer to have the front sight as red or gold colored and the rear sights with white colored paint. Regardless of the method used, these colors provide contrast with the background and therefore make the sights easier to pick up. The image below illustrates the different types of what was just discussed.

Image based off an original image uploaded by user Stannerd on wikipedia.org. The original image was licensed under the GNU Free Documentation license version 1.2 and permission is granted to copy, distribute and/or modify this image under the GNU Free Documentation licence version 1.2 or later.

Another way to make the sights more visible, especially in low light conditions, is to have the sights contain luminescent glass tubes. The most common way to do this is to fill the glass tubes with tritium, a mildly radioactive isotope of hydrogen. Tritium is also used in some luminescent watch dials. The glass tubes are also coated on the inside with a phosphorescent material. As the tritium decays, it emits beta particles that strike the phosphor coating and emit a glow in green, red, blue, yellow, orange, purple or white color, depending on the type of phosphor coating material used. Typically, green, yellow and orange are usually used with weapons. The glow from these tubes is not visible in bright light, so some manufacturers paint additional rings around the glass tubes so that they can be picked up easily during daytime as well.

There is no battery power involved here, as the glow is created by the beta particles emitted by the decaying tritium gas. Since tritium decays very slowly, such tubes have a fairly long lifespan. In fact, one well known manufacturer (Trijicon) offers 12 year warranties for their green and yellow sights. The downside to these are that the price of these is relatively higher than some of the alternatives.

Another method is to use photo-luminescent paint. Unlike the tritium filled sights, which glow at all times, the photo-luminescent paint needs to be exposed to a bright light source first, whereupon it absorbs some energy. When the light source is removed, the paint emits the stored energy out slowly and glows green in the dark. A few minutes exposure to bright sunlight or ultraviolet light is enough to keep it glowing for several hours afterwards.

The nice thing about this method is that it costs a lot less than tritium filled tubes. An existing sight can be easily converted to a photo-luminescent sight by any owner, simply by applying some adhesive strips. The downside is that it needs to be exposed to light first to work and it automatically gets discharged after a few hours and needs to be re-exposed to light again to work.

Another method that is recently gaining popularity is to use fiber optic elements. Short pieces of fiber optic cord are affixed to the iron sights. Any ambient light falling on the sides of the fiber optic cord is concentrated at the tip of the cord. Therefore, the tip of the cord glows brighter than the surroundings and makes it easier to pick up during daylight.
Typical fiber optic sights come in green and red colors. These sights are now seen on handguns, shotguns, rifles, air guns etc. Some manufacturers make sights that combine fiber optic cords with tritium filled tubes, so that the sights may be effectively used in both day and night time.

Thursday, November 4, 2010

Sights: Iron Sights: Adjustable Sights

We have recently discussed the basics of sights, as well as some history of iron sights and the two major types of iron sights, namely the open sight and the aperture sight. There are also other ways to classify iron sights. One would be fixed sights vs. adjustable sights. We discussed fixed sights in the previous post and discuss adjustable sights in this post.

The first sights that were invented were fixed sights and this was in an era where firearms did not really have as much range or accuracy. Once rifling started to become common and barrel making techniques began to improve, the range and accuracy of weapons started to increase. Hence, people found a need to have sights that could work on short ranges as well as longer ranges.

The main problem with fixed sights is that a bullet travels in an elliptical path, due to forces of gravitational pull and aerodynamics of the bullet with the wind rushing past it. Hence, for shooting at greater distances, it is necessary to point the barrel a bit upwards before pulling the trigger. Range is also affected by factors such as amount and quality of propellant in the cartridge, shape and weight of the bullet etc. Making appropriate adjustments for greater range is called elevation. With fixed sights, it is harder to decide how much to to tilt the barrel up by. With adjustable sights, this is less of a problem.

There is also movement in a horizontal direction to be considered. Due to rifling in barrels, the bullets generally tend to drift a bit from the center point. As we mentioned earlier, rifling does NOT make bullets travel in a straight line, but it gives them a predictable drift. What this means is that if you can predict for a given rifle that a bullet will drift horizontally, say, between 2-3 cm. to the right over every 100 meters distance traveled, you know that you need to compensate by the same amount to the left for every 100 meters distance to the target. There is also the need to compensate for wind blowing, which could cause horizontal deviation of the bullet. Other causes of deviation could be the profile of the bullet and its balance. Such a compensation is called windage. With adjustable sights, compensating for this becomes much easier.

The first type of sight we will look at is the leaf sight. The picture below shows a representative leaf sight.

This type of sight is fold-able for close range shooting. It also has screws for adjusting the sight in both the horizontal and vertical planes and has a number of holes in it for different ranges. This sight is mounted as the rear sight of the weapon and the front sight is fixed. To use this sight, the user estimates the distance to the target and lifts the sight. Then the user looks through the appropriate hole in the leaf sight and aligns it and the front sight to the target. The barrel of the weapon is therefore automatically tilted by the appropriate amount, as the illustration below shows:

For close range shooting, the user folds down the rear leaf sight and uses the top of the hinge as the rear sight. For longer range shooting, the user unfolds the sight and looks through the appropriate hole. There is also a windage screw to compensate for horizontal movement of the bullet.

On some weapons, e.g. the iron sights on some M-16 or AR-15 weapons, both the front sight and rear sight are adjustable. The front sight is used for fine tuning the elevation when zeroing the rifle (we will discuss zeroing sights in a future post) and the rear sight is adjustable for both elevation and windage.

Click image to enlarge.

We discussed these sights in detail previously, during our study into aperture sights.

Another popular type of sight is the tangent sight, which has been used for a number of weapons such as Mausers, Browing Hi-Power pistols, some AK-47 models etc. The picture below shows an exploded view of the parts of this type of sight on a Mauser C-96.

The part to pay most attention to is the sight leaf, which is graduated and has a V-shaped notch on the plate in the rear of the sight leaf. This V-notch is the rear sight through which the user aims the weapon. Also pay attention to the ramp and the pivot ear in the diagram above. When assembled on the weapon, the rear sight looks something like this, from the top view:

The numbers 1-10 indicate the desired range in hundreds of meters. If the slider is set at 1, this is for ranges between 0-100 meters, if set at 10, this is for ranges between 900 and 1000 meters. We will see exactly how the sight works with the next two pictures.

The above image shows the rear sight as it is set for a range of less than 100 meters. Note that the sight leaf is nearly horizontal and the sight slider is at the very back of its travel. Now let us assume that the user pushes the sight slider button and moves the sight slider forward. This is what the sight will look like in that case.

As you can see, the sight slider pushes tangentially against the ramp and pushes the back of the sight leaf upwards. In this case, the sight is set for maximum range and the rear of the sight leaf is pushed fully upwards. In order to align the raised v-notch of the rear sight with the front sight, the user needs to tilt the barrel upwards, which correspondingly increases the range of the weapon.

The third type of adjustable sight we will study is the ladder sight. The ladder sight is usually foldable. It has a movable slider and a graduated scale on one side of it to adjust for range.

Notice the top surface of the slider has a V-notch. The numbers on the graduated scale are barely visible on the right side of the ladder. To aim this weapon, the user aligns the v-notch of the slider with the front sight post and the target. The user can adjust the range appropriately by moving the slider up and down the ladder. The ladder sight is mounted on the top of the barrel and can be folded when not in use.

Another adjustable sight is the tang sight. Unlike the ladder sight, which is mounted on the barrel, the tang sight is mounted behind the action. In fact, the tang sight gets its name from the fact that it is mounted on the action's tang (the tang is the back part of the plate on which the rifle's action is bolted on.)

Tang sights can generally be raised and lowered by means of a screw thread. The above example can also be moved horizontally to adjust for windage. The bolt heads on the tang sight have a graduated scale so that the user knows how much to lower it or raise it to adjust for various distances. Like the ladder sight, a tang sight can be folded when not in use.

The more top-of-the-line ladder sights and tang sights feature precision devices like vernier scales or micrometer gauges for more accurate aiming. The picture below shows one example of a ladder sight with a sliding vernier scale. The slide is moved by turning the knob on top of the sight, which drives a screw thread.

Savvy rifle owners in the wild west would often buy rifles from Winchester, Sharps, Remington etc., but replace their default sights with one of these precision sights made by third party manufacturers, such as Marble Arms Co. and Lyman Gun Sights Co.

Another type is an adjustable folding type sight. The example below is an Matech Buis sight which can be used as an aperture sight on several rifles, such as the M4, Sig etc.

This particular sight is mounted as a rear sight and can adjust for both elevation and windage using the two knobs.

With adjustable sights, it becomes much easier for the user to aim at targets at different ranges. This is why longer range weapons feature adjustable iron sights. While most longer range weapons these days usually feature telescope sights for accuracy, adjustable iron sights are often still present as backup sights.

Monday, November 1, 2010

Sights: Iron Sights: Fixed Sights

We have recently discussed the basics of sights, as well as some history of iron sights and the two major types of iron sights, namely the open sight and the aperture sight. There are also other ways to classify iron sights. One would be fixed sights vs. adjustable sights. We will discuss fixed sights in this post and discuss adjustable sights in the next post.

Fixed sights are the first types of sights ever invented. Back in the early days of firearms, the range of weapons wasn't as much and many weapons weren't rifled either. Hence, there was not as much reason for people to have adjustable sights to adjust for elevation or windage. If a person desired to shoot at a target at a greater range, he would merely aim a bit higher, based on personal experience with the weapon.

In the early days, machining and metallurgical techniques weren't as good as today. In many cases, people simply didn't trust adjustable sights for weapons intended for rough use, because they were thought too delicate and more expensive to produce. For instance, most revolvers from the wild west used fixed sights, whereas some rifles of the same period featured adjustable sights.

In some cases, the sights were actually part of the weapon, not separate pieces. For example, on many Colt and Smith & Wesson service revolvers, the front sight was machined from the barrel's original steel blank and the rear sight was merely a groove cut into the top strap of the pistol frame. In some weapons, such as the colt paterson revolver, there was no separate rear sight and instead, when the user pulled back the hammer, there was a notch cut into it which would serve as a rear sight. Hence, weapons like these had no way to adjust the sights at all.

While we say "fixed sight", it is not entirely true that these sights are fixed. Many an enterprising owner has adjusted such sights by using crude tools such as a hammer or a file. For instance, if a revolver shoots too much to the right, the user may choose to permanently bend the front sight a bit to the right using a hammer. If the weapon shoots a bit too low, the user may file off the top part of the front sight a bit. This is why some weapons may have slightly deformed sights. This is not always due to wear and tear, but may be in that state because the previous owner took some trouble to adjust the sights to his personal preferences.

These days, many short range weapons such as auto pistols or revolvers, still come with fixed sights. For example, many models of pistols from manufacturers such as Glock, Smith & Wesson, Ruger, Colt etc. feature fixed sights.

In some cases, the sights are not entirely fixed. For example, many modern pistols come with the sights fitted on to dovetail joints. Such sights may be adjusted with special tools. Once the sights are adjusted so that the weapon is satisfactorily zeroed in, they are then left alone and are not adjusted by the user again in the field. So these sights could be called "semi-fixed" sights.