Sunday, 10 June 2012

The ultimate assault rifle: Firepower

The problem with most 21st century assault rifles lies in their small caliber projectiles, which sharply limit the damage they can inflict upon the enemy. Theres been no end of complaints over the lack of wounding potential from the M-16 series rifle, in each and every single conflict that the US military has sent ground troops into. In an attempt to justify this 5.56mm varmint rifle, military apologists will cite the high recoil and heavy ammo weight that are inherent to larger calibers. In their zest to cover up for the establishments failures, some will even place the blame for substandard performance on the soldiers themselves, spewing useless tautologys like 'its not the caliber of the shot, but the caliber of the shooter that counts.' But the fact is, shot placement has nothing to do with wounding potential. It doesn't matter how well placed the shot is if the shot doesn't do the job. If shot placement really was what it was all about, we would all CCW 22 rimfire target pistols, and the armor branch would use 25mm chain guns instead of 120mm cannons on their tanks... In a firefight, your best shot placement may often not be good enough by itself, so you stack the deck with a larger caliber. In this post, we will go over one of the most important categorys determining a battle rifles effectiveness, its firepower. This is a rigorous category which includes barrier penetration, wounding profile, and suppressive effect. When the conclusions below are taken into consideration, it can be determined that in order for any new service rifles to significantly surpass their predecessors in performance, they need to be of 7.62mm caliber.
They MUST NOT be chambered for the useless 5.56x45mm round, or an intermediate compromise cartridge like the Grendel or SPC. New recoil reduction technologys have become available which completely obviate the need for pea shooters like the M-16 or AK-74. There is no excuse not to take advantage of full power rifle ammunition. Heres an excellent quote from on the m1 garand: ''The U.S. military rifle must be powerful. That means it must be able to kill an enemy soldier as far away as the rifleman can surely hit him. It must penetrate enemy helmets and body armor easily up to the same range. It should have enough punch to tear through the side of enemy trucks and kill personnel riding within, or to destroy the engine block. The bullets of the calibre .30 rifle are relatively small and light - fine for high speed, yet heavy enough and large enough in diameter to deliver a killing blow when they get to where they are going.'' The most common 7.62mm rounds in service today (the 7.62x39mm used by russia, and the 7.62x51mm used by NATO) are not as powerful as the 30-06 rounds slung from a full 24 inch barrel. Luckily, this can be more than made up for by the ultra tight grouping that comes courtesy of a nikonov mechanism, which fires a 3 round burst at a speed of 1800 rpm. According to one source, the bullets emerge so quickly that the third bullet is out of the barrel before the recoil from the first shot throws the gun noticeably off-axis, so the net effect is that all three shots hit in a very small group, thus increasing their chances of penetration.

Hard barrier penetration
-Going by chapter 8 of the US armys FM 90-10-1, objects which provide protection from single shots of 5.56mm at distances less than 50 meters are; One thickness of sandbags, 2" unreinforced concrete wall, 55 gallon drum with water or sand, small ammo can filled with sand, a plate glass windowpane at a 45° angle (glass fragments may be thrown behind the glass), and a car body (round will penetrate but normally not exit).
-Meanwhile, single shots from 7.62mm rounds at similiar distances (relevant because the 7.62mm's optimal penetration also occurs at 200 meters) can pierce all of the materials previously mentioned, except for the 55 gallon drum. It is also unable to pierce 8" of Cinder Block, 5" of dry sand, or a 13" pine board.
-So with ONE exception (the 55 gallon drum filled with water or sand), the M80 7.62mm ball round can pierce all of the barriers that will stop the M885 5.56mm AP round. The 7.62mm rounds penetration was also less affected by short ranges to the target (5.56mm rounds need time to stabilise their flight path: If they don't get that time, their barrier penetration is heavily compromised), and the penetration increase that came from using AP rounds was greater with the 7.62mm than the 5.56mm. Note this is for a single rounds: A full auto weapon of any caliber is like a jack hammer, in that the burst will wear away at walls. With enough time and ammo, a 7.62mm or even a 5.56mm will eat through most any amount of concrete. AP bullets are supposed to do a little better but more likely to ricochet. Rebar will help a lot against any caliber because they have to break concrete and then cut rebar.
Suppressive effect
-According to the royal united services institute, suppression is the effect of small arms and other weapons systems which temporarily prevent the enemy firing its weapons or moving in the open. In simple terms, it makes them keep their heads down, and loose fire superiority. Suppression is critically important in a fire fight. In the offence it allows the attacker to move forward, to find gaps and weak points, and exploit them. In the defence it prevents the enemy moving forward and firing, and thereby sets him up for counterattacks. In both cases it pins the enemy down for incapacitation (or destruction) by other weapons. The key to winning a fire fight, then, is by securing fire superiority. Whoever has it wins because they have outgunned the enemy. Fire superiority does not necessarily entail a higher volume of fire. Rather, it means that one side has forced the other side to seek cover, so in effect, fire superiority is fire intimidation. This can be accomplished through a high volume of fire, more accurate fire, or the use of 'shock and awe' weapons.
-Both experimental and practical testing has revealed that the suppressive effect of a small-arms bullet is directly proportional to the loudness of the sonic bang it generates, which is in turn directly proportional to its size. 5.56 mm bullets have only half the suppressive radius of 7.62 mm fire, and this is exacerbated by the fact that the little bullets are more affected by wind drift and therefore less likely to get close to the target at long range. Another factor that must be taken into account is the weapons cone of fire: When several shots are fired in a burst from an automatic weapon, each round takes a slightly different trajectory. The dispersion pattern these rounds take on their way to the target is called the cone of fire. This is influenced mainly by vibrations from the weapons recoil, and variations in the ammunition. Wind drag and other atmospheric conditions also play a role. Why does this matter? Back in 1944, a study carried out by the army operational research group concluded that projectiles must not only pass within a certain proximity of a human combatant, but also arrive in a certain volume before he will feel threatened enough to take cover. Threfore a rifles effective range (against point targets) is determined by its MOA accuracy, which for the M16 rifle is 550 meters.
Wounding profile
-This is a rather lengthy and complex subject, but its basic concern is maximising the injury potential of a bullet once it makes contact. During its passage through the enemy combatant, the bullet must cut as wide a swath as possible, so that the target will be down and out of the fight afterwards. Such damage stems from two primary mechanism: A permanent cavity, and a temporary cavity. The permanent cavity is the volume of flesh the penetrator comes into contact with and crushs, leaving a permanent hole in its wake. The temporary cavity is the volume of flesh which flexes and stretchs as a result of the pressure wave transferred by the bullet to the bodily tissues. All organs are susceptible to damage from a permanent cavitation, while only some are vulnerable to temporary cavitation. Organs which are of low density and high elasticity (such as the lungs, an empty bladder or stomach, etc) will be unfazed by its effects. Organs like the brain or liver, however, will rupture spectacularly when subjected to such a pressure wave, with devastating consequences for the victim.
-Although permanent cavitation is directly dependant on the size of the penetrator, other factors such as its flight path through the targets body have critical importance. When entering a dense medium, bullets have a tendency to destabilise and flip over, so that their base (rather than their nose) points forward. This has negative consequences for the gunshot victim. The wounding profile will be significantly enlarged, as will the number of structures that the bullet comes into contact with (and destroys). Not all bullets act the same when travelling through bodily tissues, though. Some are more stable than others, and do not experience yaw until exiting the body. Others transition between their stability points (from the nose to the base) very quickly, minimising their damage potential. What is desired, then, is a bullet which yaws almost immediately after entering a targets body, and maintains that yaw for as long as possible, inflicting the maximum amount of damage.
-Temporary cavitation, on the other hand, is more dependant on the penetrators hydrodynamic profile. For reference, while an increase in velocity will increase the temporary cavity size, it will not increase the permanent cavity size. The stretch marks that TC produces in ballistic gelatin, though visually engaging, can be resisted by those bodily tissues which are more elastic than gelatin. In most cases, temporary cavitation is unlikely to cause anything more than some internal bruising. Speculative sources state that nerve bundles can be damaged by temporary cavitation, creating a stun effect, but this has not been confirmed.
-When all is said and done, permanent cavitation is the most reliable way of inflicting damage on a target, regardless of what the targets particular composition may be. Temporary cavitation is unreliable and finicky, merely a beneficial side effect at best. As it pertains to wounding profiles, a larger bullet can thus be seen as not just deadlier, but more dependable, too. Unfortunately, bullet size is a means to an end, not an end in itself: It is a base that must be built upon with proper bullet design, taking into account things like sectional density, center of gravity, hydrodynamics, etc. The job of procurement officers, then, is to get a 7.62 mm caliber weapon into service: After that, the concern of how its projectile behave inside dense mediums will be tackled by ballisticians.

   How the two most common NATO 
rounds (7.62mm top, 5.56mm bottom) 
perform in the human body

-Now, to determine which round has superior ballistic performance: The 7.62mm, or the 5.56mm. Looking at the numbers, the 5.56x45mm nato rounds can be seen to trade momentum (stopping power) for kinetic energy (shock). And unfortunately, from a mathematical perspective, kinetic energy is always overemphasized. Recall that momentum is mass x velocity, but kinetic energy is mass x velocity squared. If the velocity of an object is tripled, then KE is more than qaudrupled, but momentum is only tripled. This reality escapes most people. A quick word on terminal effectiveness: Military ammunition cannot legally take advantage of the expanding bullets used commercially for hunting, which can inflict devastating injuries.
-So military bullets rely on a ‘yawing effect’ to maximise their effectiveness. ‘Yawing’ describes what happens when a pointed bullet enters a dense medium like a human body: It will usually become unstable (turning sideways) before travelling base-first through the target. This ‘bullet upset’ greatly magnifies the size of a wound, making it more likely that the target will be rapidly incapacitated. However, the effect is unreliable. If a bullet yaws rapidly after impact it can inflict severe wounds; but if it fails to yaw before the bullet exits the body, the resulting small hole may only have a limited effect unless a vital organ is hit. In the case of the 5.56mm rounds, some soldiers have likened it to shooting needles. Several hits may then be necessary to neutralise an enemy; There have even been cases where enemy combatants have got back up after being shot multiple times. In these circumstances, the bigger the bullet, the better.
-This is true for several reasons. First and foremost is that, whereas the 5.56x45mm is largely dependent upon high velocity in order to wound effectively, the 7.62x51mms wounding ability declines at a very steady and predictable rate with increased distance, making it more dependable. The second is that a large slow projectile will crush (permanent cavity) a large amount of tissue, whereas a small fast missile with the same kinetic energy will stretch more tissue (temporary cavity) but crush little: Permanent cavitation should always be desired over temporary cavitation. The third is that a heavy bullet is far less likely to be deflected: There is no point in having good shot placement if the bullet takes a random path as soon as it encounters a rib or pocket of change. In this area, an increase in bullet weight is more beneficial than one of velocity. After all, pushing a bullet through several feet of meat requires a sustained pressure, and a heavy round has more inertia. A heavier bullet will also have (proportionately) more of its original energy by the time it reaches the target.
-Examinations on the terminal performance of both the 5.56x45mm M855 rounds and the 7.62x51mm M80 rounds conclude that neither is likely to experience ANY yaw in an average human body. Regardless, the insurmountable advantage that a larger bullet retains is wisely noted by the FBI academy firearms training unit: "Given adequate penetration, a larger diameter bullet will have an edge in wounding effectiveness. It will damage a blood vessel the smaller projectile barely misses. The larger permanent cavity will lead to more tissue disruption and faster blood loss. Although such an edge clearly exists, its significance cannot be quantified."

Experience has shown that while the 5.56mm is a good killer, it is not a good stopper. One properly placed shot from the 5.56mm is just as likely to kill someone as any other major caliber rifle, but it will do so slower, and leave the subject more functional while they are dying. This is unnacceptable in an infantry weapon. It has poor barrier penetration, poor suppressive effect, and to make matters worse, the 5.56mm round suffers from low inertia, meaning that its flight path can be disrupted by vegetation on the way to its target. The same property that lets a light bullet be accelerated more readily also means that it can be more easily slowed by the air it is passing through, and knocked off course by foliage, cross winds, etc.
So what then are the consequences of adopting a larger caliber like the 7.62x51mm nato? There are a couple that come to mind. There is the heavier recoil. A 7.62mm round will have twice as much kick as a 5.56mm round. This can be compensated by introducing the balanced automatic recoil system, or a nikonev mechanism, into the rifles gas operating system. Then there is the fact that the cartridge is twice as heavy, so fewer rounds can be carried for a given weight, although the force of that argument is much reduced if it is necessary to fire more 5.56 mm rounds to achieve the same effect.
For some background information, weapons that use BARS have less recoil in sustained firing because it eliminates 3 of the 4 stages of recoil operating on a firearm. The only recoil felt is the force operating on the barrel itself and not the inertia of the bolt group moving backward, hitting the back of the rifle, and then moving forward again; those stages of kickback are eliminated. It achieves this through the use of a recoil-reducing countermass mechanism with two operating rods that move in opposite directions, thereby providing "balance." This would be a great advantage when using fully automatic fire to rapidly clear out confined spaces such as bunkers, trenches, and rooms.
*edit made may 17, 2013