A Primer on Modern Personal Firearms: from Shotgun to Sub-Machine Gun, and more from WW1 to Modern Times
Personal firearms are generally defined as projectile weapons shooting bullets powered by gunpowder or smokeless powder, that can be operated by a single person. We know them as pistols, revolvers, submachine guns, assault rifles, rifles, machine guns, shotguns, and so on. They each evolved out of different needs and compromises, based on the technology available, coupled with hard-fought battlefield experience. Their purpose is still best summed up by General George S. Patton: "You don't serve your country by dying for your country. You serve your country by making the other poor sap die for HIS country." (slightly paraphrased).
A personal firearm is a lethal instrument. It is meant to cause death and destruction. Thus, any firearm discussion must be related to its capability for that.
This is NOT a game guide. This is about real weapons and how they evolved as weapons. This is about reality, not the fantasy world of games.
Following factors must be considered for all weapons: range, accuracy, volume of fire (firing speed AND time to reload), overall size and weight of weapon (with normal "combat load" of ammo), and later, lethality of the round (muzzle velocity, kinetic energy, and so on). Actually, there is another factor: ease of use, but that can be overcome by training. Let's start with the venerable "rifle".
NOTE: the bullet, is what comes out the gun barrel. Cartridge (also known as "casing"), is where the propellant is stored, and together they are called a "round".
American Army in WW1 deployed the very secretive "Pedersen device", which is a special modification to their M1903 Springfield bolt-action rifle. When installed, it allow the rifle to fire from a 40-round box magazine semi-auto. It was never actually sent into combat, and WW1 ended without it seeing any actual action, and all the devices were scrapped after the war. The device was an inspiration to Garand for the M1 rifle.
Barrett M82 .50 caliber rifle
The Barrett .50 cal is NOT really meant to shoot people. It is considered an anti-material rifle, in that it is meant for a shot into the engine block of a car or truck, or into the engine of an airplane, and so on. One bullet is enough to disable a plane or a truck. While it works great on people, keep in mind that a kill shot is much harder to arrange than a shot against an inanimate object.
The Largest Sniper Rifle?
In World War II, some "anti-tank rifles" are literally large rifles, and they were able to punch through light tank armor at the beginning of the war. The Finns were famous for their Lahti M39 which held off the Soviet invasion in 1937, and the Japanese fielded a Kawamura Type 97, both of which are chambered for 20mm rounds.
The 20mm round super rifle is enjoying a revival with the launch of Anzio Ironwork's Ultra-Long-Range Sniper System, that will go BEYOND 3000 yar ds, perhaps as far as 3500 yards, with a modern 20mm sniper rifle, that reaches beyond even the vaunted Barrett .50 cal sniper rifle.
Rifle and its cousins
A military rifle is not that different from a civilian hunting rifle. What is different is the caliber, ammo, and design tolerances. What is common for all rifles is they are two-handed weapons, and require shoulder-stock to absorb the recoil. This is due to the power of the rifle round. Most modern rifles can propel a projectile with muzzle velocity of 2500-3000 ft per second, and the round will remain stable out to several KILOMETERS. In the present-day military, a rifle is relegated to the exclusive realm of specialist snipers, and known as "sniper rifle". This is due to several reason: very long range (the world record is 2.43 kilometers confirmed kill), and very slow rate of fire (even with a trained operator, you're talking maybe one round every few seconds). Keep in mind that during the American Revolutionary War, and a little later, they were using muzzle-loading muskets that takes 30-seconds to a minute to load one shot!
In World War I, all armies were using one type or another of "bolt-action" rifle, which must be manually cycled to load the next round. If you remember "Saving Private Ryan", the American sniper was using a Springfield bolt-action rifle outfitted with a telescopic sight. Yes, I know that's World War II. Bolt action rifles don't have anything moving except the firing pin while shooting, so the whole thing is stable, increasing accuracy. The trade-off is very slow rate of fire. Most use some sort of a "loading clip" so you can load 5 or so rounds at a time, but cycling is still manual.
Pros: very long range, very high accuracy
Cons: very low volume of fire, heavy weight and relatively few rounds carried
Almost all armies entered WW2 with same bolt-action rifles from WW1, except the Americans, who deployed the M1 Garand, which is semi-automatic. That means you don't need to recycle the bolt to fire the next round! Just keep pulling the trigger and you'll keep shooting until you run out of ammo in the clip (8 rounds for the Garand). Semi-automatic weapons tap some of the exhaust gas in the chamber to extract the spent shell, which allows the new round to be pushed into the chamber and locked. There are variations, such as direct impingement, piston push, and so on, but they operate by the same general principles.
Pros: long range, high accuracy
Cons: low volume of fire (but much higher than bolt-action), heavy weight and relatively few rounds carried
The semi-auto rifle have a problem gaining acceptance, due to two factors: logistics, and tradition. It was feared that any attempt to increase the rate of fire would increase the load on the logistics system, as the soldiers will not have to aim as carefully, but just shoot randomly into the area. Also, tradition dictates that the soldier should not waste ammo, "one shot one kill" was the motto. It took many years to get the M1 Garand fully accepted. And even then the M1903 Springfield bolt-action never left the inventory.However, Garand became a legend, and was one of the best instruments of war according to General George S. Patton.
Modern sniper rifles can be either bolt-action or semi-automatic. Both have their proponents and opponents. There are many variations. The M40 is bolt-action, and its European counterpart, the Accuracy International AW (Arctic Warfare) rifle. A semi-auto sniper rifle would be the the Soviet Dragunov, the M14/M21, Barrett M82 .50 caliber rifle, and the SR-25. Modern technology have improved the accuracy of semi-auto snipers rifles so that they can offer the same accuracy but much higher firing rate. Some Russian special forces operators have remarked that they believe the semi-auto nature of Dragunov sniper rifle allowed them to save more lives during the Beslan School Siege when they need to engage more targets faster.
Browning Automatic Rifle (BAR)
US Army deployed the BAR (Browning Automatic Rifle) during WW1 and WW2. It fires from a 20-round box magazine, but it is quite unwieldy, being even LONGER than a normal rifle, and is really meant to be fired from the bipod while prone. It can be fired by a single person like an oversized rifle from the shoulder, but the limited magazine capacity makes it somewhat less than a true machine gun.
The "Stinger" Improved LMG
US Marines during WW2, actually improvised a LMG by taking the rear pintle-mounted machine gun out of an Avenger dive bomber, adding a rear stock and improvised trigger, and a mid-mounted handle, and a bipod, and turned this mounted weapon into a one-man portable LMG. They named it "Stinger". It is still fired from the hip, but deadly in close range.
It is possible to make rifles into fully automatic weapons, but they became very unwieldy as you need a heavily weighted tripod base to provide a platform to act against the recoil.
One of the first successful attempt to make a fully automatic rifle is known as the Gatling gun. Invented by Dr. Gatling in 1861, it basically combines multiple barrels with mechanical synchronization of feeding the round, trigger the round, and ejecting the spent casing, to achieve continuous fire. It technically is not a "machine gun" as someone must continue to power mechanism to continue feeding / trigger / eject sequences, but it is a tremendous leap forward in terms of weapons technology.
Pros: HUGE volume of fire, decent range, reliable, almost jam-proof
Cons: VERY VERY heavy (considered a small artillery piece), consumes ammo very quickly, requires power source (manual crank or power)
A gatling gun is NOT a personal weapon. Even the smallest version, i.e. the "minigun", i.e. the weapon wielded by the Terminator in T2, or in Predator (the movie!), can only be wielded by the strongest men. It is basically a machine gun, with rotating barrels, so the high rate of fire doesn't heat up the same barrel, and the rotating motion also helps with the cooling. However, it requires a power source (to spin the barrels) and a HUGE supply of ammo.
Gatling gun initially were considered small artillery pieces (i.e. like a small cannon) and are deployed on small carriages as such. You can still see them in some Western movies. They are extremely heavy, and are almost always mounted on a carriage or a vehicle. They typically achieve over 1000 rounds per minute. General Electric tested one of the museum piece Model 1903 Gatling in 1946 powered by an electric motor. This piece momentarily achieved 5000 rounds per minute.
The problem with Gatling gun is they are not portable at all, and something smaller is needed. Hiram Maxim is the first. with the Maxim machine gun in 1882. John Moses Browning came along a little later with the M1895 Colt-Browning Machine gun.
A machine gun is not man-portable, at least in WW1's time. They are known as "heavy machine guns", and fire rifle-type bullets. The Vickers (British) and the Maxim (German) are both based on the American Hiram Maxim's design, but they ended up on opposite sides of WW1. Usually, one man carry the gun itself, one man carry the tripod, and one man carry the ammo belts.
Pros: high volume of fire, decent range
Cons: VERY VERY heavy (takes up to 3 people to move one), consumes ammo very quickly
There were attempts to make them lighter and more portable, but most of that didn't work too well until WW2, and by then it is STILL a 2-man weapon (gunner, and ammo/barrel carrier). That is the "light" machine-gun, and that's still in the 30-50 pounds without ammo! Another problem is so many rounds going through the barrel heats it up to dangerous levels. A lot of WW1 machine guns are water cooled, and generates steam when overheated (giving the enemy a great target for mortars or snipers). If you don't cool the barrel, the barrel will warp, which affects the accuracy, and can even cause a jam inside the barrel, and that's BAD, VERY bad, even exploding the barrel.
BY WW2 most machine guns are air-cooled, with additional tricks to help cooling. The German MG38/42 have quick-change barrels that you can just "snap out". (And American units have learned to draw fire, until the Germans overheat their barrels, THEN rush the MG position with grenades) Other guns have to artificially slow down the firing rate to increase barrel life, or introduce "radiating fins" and such for air cooling. However, they are still meant to be fired from a bipod, with an operator prone on the ground, firing short bursts.
In desperate times, the standard LMG *can* be fired by cradling the barrel in the crook of the elbow, essentially doing a "Rambo". However, firing from the hip is NOT good for accuracy.
Rifles are long-range weapons, and are unwieldy in urban environments. There are some attempts to make reduced length rifles, which are known as "carbines" (initially made for cavalry troops, as full-size rifles are unwieldy on a horse). However, those are still two-hand weapons.
Carbine: a short rifle, originally created to be used by cavalry on horses. Nowadays they refer to a shortened assault rifle.
Another variant is the "automatic rifle", basically rifle capable of firing on full auto. After WW2, US tried to make a rifle that is capable of automatic fire. However, the M14, which is basically a M-1 Garand modified to full-auto, and a 20-round magazine, was way too powerful to be controllable on full-auto without extensive training. Today, the M14 enjoyed a resurgence as a semi-auto "sniper" rifle.
There is always a need for a simple one-handed weapon, that is simpler to use and easier to move for shorter ranges, and that is where the pistols become very useful.
Bullpup is a configuration, not a specific model or type of gun. Normal gun configuration have the trigger very close to the chamber and the "action". By moving the trigger and handgrip forward, and making the "chamber" a part of the shoulder stock, even a long barrel weapon can be made "compact". On the other hand, reloading is slower due to the magazine now located behind the trigger group, and the gun's weight is shifted rearward. Ejecting the spent cartridge becomes a bit of a problem.
The most famous "Bullpup" design is probably the Steyr AUG, a very futuristic weapon first seen in the movie Die Hard (the original). Please note that a weapon in bullpup configuration is NOT necessarily considered a carbine. The Styer AUG itself can be had in carbine version, known as the Styer AUG Para (for paratroopers), with slightly shorter barrel (by several inches).
Pistols and variants
Pistols are defined as weapon that is held and fired by a single hand. Due to the short length of the barrel, and the limit of stability of a single hand, pistol rounds are generally much smaller than rifle rounds. The problem with pistol is limited range and accuracy due to short barrel. Pistols are not meant for targets at greater than 50 yards range. They are usually issued as "sidearms", or a "secondary weapon".
Keep in mind that pistol rounds are SMALLER and fire at slower velocity than rifle rounds. Most rifle rounds are well over 2000 ft/s (usually, 2500 to 2800 ft/s), while even the most powerful pistol rounds are only about 1500 ft/s.
Different countries developed different pistol rounds. The Americans originally liked the .38 for their revolvers, later changed to the .45 ACP (the "Colt .45") for superior stopping power. The Germans prefer their 9mm Luger "parabellum" ammo.
Pros: light weight, can carry many rounds,
Cons: very low range and accuracy, low volume of fire
There are pistols out there that are capable of 3-round bursts, or even full-auto fire, but they are not controllable without additional bracing, and their limited magazine capacity makes it unpractical. The Berreta 93R has a folding front-grip so it can be used as a two-hand weapon, and even has an attachable shoulder stock. The three-round burst is so fast, it is often thought of as a single shot, making it the ideal weapon for Robocop. Another full-automatic pistol, probably the Glock 18, was used by Morpheus in Matrix Reloaded.
Many researchers sought to bridge the two extremes of pistol and rifle. Those starting from the pistol created the submachine gun (and the machine pistol), and those that started from the rifle created the assault rifle. And then of course, there's the shotgun, normally a hunting weapon, but very lethal in close quarter combat.
Submachine gun is named because they are fully automatic like machine guns, but firing a smaller / weaker bullet than a "true" machine gun. As the bullets are smaller, and that's refer to as a "sub-caliber", thus, sub-machine gun.
Pros: good volume of fire
Cons: low range
The first submachine guns are robustly designed and actually quite hard to manufacture, as they are basically miniature machine guns shooting pistol rounds. It took a lot of research and industrial power to create easy-to-make submachine guns. The MP40, one of the iconic German weapons of WW2, was made mostly of stamped metal. The American Thompson SMG was so hard to make, that the US created the M3 SMG, often called the "grease gun", which is MUCH easier to manufacture (takes about 1/10th the time). The Brits started WW2 with no submachine gun, having regarded it as a weapon for criminals. The Brits had to copy the German MP18, a WW1 German design, for their "Sten" submachine gun.
The best known submachine guns today are the Israeli Uzi, and the H&K MP5 series. The Uzi looks like an over-sized pistol, and the magazine is fed through the handgrip (like a pistol). The basic shape is very iconic, and almost any submachine gun with that shape, such as the American Ingram 10 SMG, are often called an Uzi. And that is just wrong.
The H&K MP5, on the other hand, looks like a short assault rifle, sharing the basic shape with the StG.44, the first assault rifle. In fact, the MP5 was derived from StG.45 prototype, a proposed successor to the StG.44 but never fully developed during the final days of WW2. The basic MP5 design allowed itself to be adapted to various calibers. The base MP5 is 9mm, though it is also available as .40, .45 ACP, and so on.
Most submachine guns today are actually assault rifles redesigned to fire pistol ammo, instead of scaled up pistols. This gives them improved accuracy and more robust operation, and less prone to jamming.
In modern days, there is a distinction between the "machine pistol" and the submachine gun, but the line is a rather blurry one. A "machine pistol" usually is a pistol capable of automatic fire, with detachable shoulder stock, while a submachine gun is a carbine-style folding-stock or fixed-stock weapon that resembles a small assault rifle. The Uzi appear to be an exception, but most people don't see the forearm bracing detachable stock being used.
Alternate Shotgun Ammo
The large shell size and smoothbore nature of a shotgun makes it easy to adapt the shell to other uses. Solid slugs are great for door busting (ever seen the movie Equilibrium?). When loaded with reduced load shells firing "plastic" slugs or "beanbags", it became known as "less than lethal" weapons. Taser International is developing a self-contained Taser shotgun slug that can deliver a 10 second pulse jolt to a perp over distance of 50 yards, much better than current distance of 5 yards with the current Taser. Even the solid slugs can be made in "frangible" form, which means it is solid... but only until it hits something solid. After which it fragments into powder. It will penetrate whatever you're hitting, but it won't go beyond that. Which makes it ideal when shooting in delicate places, such as inside airplanes (don't want to punch holes in the fuselage), or inside factories (pipes and such), where ricochets and penetration can be a problem.
Shotgun fires a load of "shots" from a single large shell, spread out in a cone across the front, through a smoothbore barrel. It is devastating in close range. It was originally a hunting weapon (the historical name is "fowling piece", to shoot birds). American forces in WW1 brought 12-gauge shotguns with them for trench clearing. Seeing the shotgun's effectiveness in close quarters is reputedly one of the reasons why the Germans designed the submachine gun, to outdistance the shotgun user and still have a huge volume of fire.
While shotgun has a low rate of fire, the number of "shots" fired at once actually gives it a good volume of fire. The problem is lousy range, even LESS than that of a pistol, maybe 25 yards, if not less. However, it has a good engagement cone, allowing one to engage multiple enemies at the same time.
Most shotguns have a tubular magazine that can only be fed one shell at a time, so reload time is very long, until later advances fixed that.
Pros: great volume of fire, until the magazine runs out
Cons: VERY lousy range, long reload time (unless magazine-based)
Most shotgun requires manual loading. In Terminator 2, both T-800 and Sarah Connor were using manual shotguns (one's a lever action, and the other is a pump action). Later semi-automatic shotguns were created, and then even later, the automatic shotgun was created, and there are several... the Streetsweeper, the Neostead, the CAWS, the mostly experimental Pancor SledgeHammer, and the most recent and popular, the AA-20. Those offer absolutely DEVASTATING volume of fire up-close and personal. Eastern Europe also have their variants of automatic shotgun as well.
An assault rifle is an attempt to introduce a two-handed single-person "machine gun". It was recognized then that the rifle cartridge is too powerful, so a "reduced" version must be used, and the Germans in WW2 was the first to design such a cartridge and weapon. Germans recognized the need for a weapon that in semi-automatic fire, can still engage accurately targets out to 300 yards, but in close-quarters, capable of full automatic fire, and be carried and fired by a single person, preferably magazine-fed. Hitler almost single-handedly derailed the project. Only after enthusiastic reception by his forces, and misrepresentation by his weaponeers (as a machine pistol) that he eventually and reluctantly accepted the weapon. Even then, he renamed it "storm rifle" (sturmgewehr), though it's probably better translated as assault rifle, the StG-44.
The Soviet AK-47 was very much inspired by the German StG-44. It fires a bullet same caliber as their Moisin-Nagant rifle, but shorter.
The American gun designer Eugene Stoner decided to go at a different direction in the 1960s with his new invention, the AR-15. The AR-15 fires a 5.56mm bullet, which is essentially .223 caliber. While the bullet is small, the velocity of the bullet is much higher, up to 2800 ft/s. Also, the bullet is just stable enough via the rifling of the barrel to be accurate out of several hundred meters, yet bullet actually tumbles upon hitting anything solid, thus causing much bigger wounds than the small caliber bullet would suggest, making it just as lethal as a bigger bullet. The higher velocity bullet also makes the shots more accurate and less susceptible to wind and other environmental factors, while the lighter bullet makes the recoil much more manageable. The US military eventually adopted the AR-15 as M-16 in time for Vietnam War.
Pros: somewhat accurate in semi-auto out to medium-long range, still capable of full-auto close-in
Cons: neither as light as submachine gun, nor as powerful as battle rifle
The Soviet Union was so impressed with this smaller/faster bullet idea, they created the AK-74 (using a 5.45mm bullet) and completely replaced AK-47's in their army.
The cross-genre weapons
The PDW, or "Personal Defense Weapon" is a new genre recently coined as a super-compact submachine-gun, that offers better firepower and magazine capacity than just a pistol, but not too much larger than a pistol, so that no extensive training is needed for optimal use. It is meant to be a weapon of "desperation", as defined by NATO. Recognizing that pistols don't have enough firepower, PDWs are issued to people who don't normally carry assault rifles, such as specialists, drivers, pilots, and so on. Basically, it's a cross between a submachine gun and a pistol. In the movie Stealth, Jessica Biel's character was carrying a PDW during her escape and evade attempt.
TRIVIA: The assault rifle carried by the guy was the H&K G36.
Genres are never "set in stone". A gun company can always call their gun something when convention says it should be called something else. And recently there are a lot of genre-busters and genre-benders either by clean-slate rethinking or by creating yet another in-between category.
One example is the P90, which fires a new 5.7mm round. It is considered a submachine gun, mainly because there's also a pistol, known as the FiveSeven, that uses the same rounds. But these rounds are nothing like pistol ammo that came before. They are more related to 5.45mm assault rifle rounds.
Another is the 4.7mm PDW rounds. By shrinking the 5.45mm round in both caliber and length, the weapon can be made more compact, while the velocity of the bullet remain high. A burst can still penetrate body armor at respectable distances.
Another is the new 6.2mm Grendel round, and the .338 Spectre round, as a compromise between the small 5.56mm round and the big 7.62mm round. It offers better knockdown power than the lighter 5.56mm rounds while being not quite as unwieldy as the 7.62 rounds. Think of it as a cross between the large caliber assault rifle and the small caliber assault rifle, or a compromise between a battle rifle and an assault rifle.
Then there's the .50 action express rounds, for the Desert Eagle. These are NOT the 50 caliber bullets used by the big Barrett rifles. These are bullets that fit in a rather large pistol that is known to many Counterstrike gamers as the "Deagle", in order to scale up the bullets from one of the most powerful pistol ammo: .44 magnum.
For those who need heavy bullet, but still in assault rifle form, there is the .50 Beowolf rounds. With some matching parts, you can convert almost any AR-variant into a .50 caliber assault rifle. While the magazine capacity is reduced, the heavy punch makes it great for stopping cars, punching through doors and walls, or even just general CQB: Close Quarter Combat.
A total rewrite of rules is the MetalStorm system. Instead of using a single chamber to shoot and reload bullets into the chamber, it simply "stacks" multiple bullets in the barrel itself. In fact, it can use multiple barrels also. By using electronic trigger and ignition, a burst can be fired so fast, there is no TIME for recoil to act. It is still in prototype stage, but the system shows promise, as it loses some accuracy, but adds tremendous amount of firepower. It's almost like having a Gatling gun, in the size of an large assault rifle. To reload, you simply replace the whole barrel(s).
The Lethality Debate
There is always a debate on which is better, and the personal guns are no different.
In the early 1900s, when the US is trying to pacify the Philippines, their .38 revolvers are not taking down the rebels charging at them, often requiring multiple shots. They had to switch to "Colt .45" firing the .45 ACP to get reliable stopping power. That is when people discovered "stopping power", or "lethality". And there are a ton of factors affecting lethality.
How do you measure lethality? That is a very good question, and the jury is still out. As the .45 is found by combat experience to be superior to the .38, we know .45 is "more lethal". However, WHAT makes the .45 ACP more lethal? There are three factors to consider: weight of the bullet, velocity of the bullet, and finally, motion of bullet at and after impact. Other factors to consider would be bullet deformation and fragmentation, hydrostatic shock, and penetration.
The weight of the bullet is important, because it is the only part of the weapon that actually hits the target. The heavier the bullet, the more the target will feel it (assuming same muzzle velocity). That's the difference between getting hit by tennis ball (which is hollow), vs. a baseball (which is solid). However, the bigger the bullet, the harder the recoil, and harder it is to control.
TRIVIA: When you get hit by a bullet you don't fly back X number of feet. It looks good, but it's not real. Busted by Mythbusters already.
The velocity of the bullet, often known as "muzzle velocity", is also important. Faster the bullet, the more accurate it is, because the less you have to worry about wind, gravity, air density, and so on. However, higher velocity bullet means you need special aerodynamics design for the bullet, as well as tighter tolerances for the gun's internals.
(Together, the weight and the velocity gives you the momentum and/or the kinetic energy as the bullet leaves the muzzle)
And finally, the bullet does not necessarily go straight through. A bullet can "tumble" in mid-air, as it loses aerodynamic integrity (the spin stabilization slows to the point it is no longer flying straight) So it can actually hit a target sideways, backwards, or somewhere in between. Which means even a small bullet can actually cause a big hole. The more rifling spin you add, the more accurate the round, but the less likely to tumble. Conversely, the more the bullet tumble, the less accurate it is.
The issue gets even further complicated once the bullet hits the target. The bullet can fragment, or deform (bend into different shape) further complicating the damage it can cause to the target. The "hollowpoints" have the tip of the bullet scooped out. This cause the bullet to flatten upon impact, creating a much larger exit wound than entry wound. It supposedly was so horrific, it was outlawed by the Geneva Conventions. However, some modern military bullets are technically hollowpoints. They are "legal" because the hollowpoint is there for aerodynamics, not for target wound capability, but they are technically hollowpoints.
To further confuse the issue, there's the problem of "hydrostatic shock". The idea is the bullet actually cause shock damage to the body. Remember, human body is 70% fluid, so if a bullet can setup a hydrostatic shockwave, one can damage all the organs inside the chest cavity without actually hitting all of them. Some say this is actually a myth, while others say it's real, but not as strong as the proponents claim.
Then there's the problem of penetration. You don't want "over-penetration", because if the bullet punches THROUGH your target, you may do damage to stuff you did NOT target! On the other hand, many enemies now wear body armor, so you want your bullets to be able to punch through THAT. Confused yet? These are ALL factors affecting lethality.
The 5.56mm (.223 caliber) bullet used for the M-16/AR-15 series have gone under increasing criticism for "lack of lethality". However, the problem is not the bullet, but the gun. It has more to do with the deployment of the M-4 carbine, a short-barrel version of the M-16.
The M-16 have a pretty long barrel, and it has just enough spin to keep the bullet stable out fo about 300 meters, and the not so much spin so bullet will tumble upon hitting something. By comparison, the M-4's barrel is 25% shorter, which means you get 25% less spin on the bullet, and the muzzle velocity is significantly less, for the same bullet. In order to compensate for the decreased accuracy due to 25% less spin, the weapon maker increased the rifling spin rate. However, as a result the bullet no longer behaves the same way it does in a M-16. It no longer tumbles in the same range, and behaves differently when it hits the target. The Army judged that it's better to hit the target (i.e. have accuracy) with round that's less lethal, instead of inaccurate round that's more lethal.
M-4 is NOT a bad gun. For CQB it is more appropriate than the long-barrel M-16, and the system itself is combat proven. However, you can't just put out a new gun system and expect it to behave like the old one just because you kept the caliber and the moving parts the same. A barrel is a big part of the gun, and changing it will have a major effect on the way gun operates. M-4 is NOT the same gun as the M-16, and thus, trying to use M-4 like a M-16 will not yield the same results.
I hope this primer on personal firearms has been somewhat useful. If you have any questions of comments, feel free to post them in the comments, and I will try to answer them to the best of my knowledge.