The Assault Rifle

Six comparative views (left to right) of the 7.92×33mm MKb.42(W), MKb.42(H), and the MP.44.

Polte Company drawing of the 7.92mmx33mm kurz Sturmgewehr cartridge (all dimensions in millimeters). The Sturmgewehr and its intermediate cartridge, the 7.92x33mm Kurz (Short), gave the individual soldier vastly increased firepower by two attributes that neither the rifle nor the submachine gun could combine: controllable burst fire and good ballistic performance. It inaugurated a new concept in small arms: a short, handy shoulder weapon having a reduced recoil impulse that allowed accurate full-automatic fire, yet powerful enough to serve as a conventional rifle out to 400 yards- the range within which most infantry engagements occurred. This combination was achieved by utilizing a cartridge midway in size and energy between the relatively weak pistol round used in submachine guns and the full-power infantry ammunition common to then-standard rifles and machine guns. The smaller intermediate cartridge allowed the Sturmgewehr’s mechanism to be more compact, lighter, and less expensive, while the reduced weight of both gun and cartridge meant that the soldier could carry more ammunition into battle. Today virtually all infantry rifles embody the Sturmgewehr concept.

The universal application of the automatic principle to the individual weapon has made it necessary and convenient to give that weapon a new name, thus indicating its enlarged capabilities — the assault rifle.

Widespread use of assault rifles, particularly during the past five decades, has shown this individual weapon used by all adversaries involved in past and present conflicts; whether guerrilla wars, civil wars, “wars of liberation” and certainly by major combatants in larger wars. The increase in firepower for the individual has literally provided small groups of determined men armed with selective-fire assault rifles the force that here-to-fore was reserved for battalions and regiments.

When hand-held fully automatic weapons fed by detachable magazines first came on the scene, they were made in existing infantry rifle calibers. Some, such as the FN/FAL and U.S. M14 rifles, continued in such calibers until the advantages of an intermediate round — such as controllability on full automatic fire — were irrefutably demonstrated by the Kalashnikov AK-47. The early iterations of the assault rifle concept, such as the Federov, the BAR, the Simonov AVS-36 and others served to illustrate how advantageous such a design might be, but it was not until the German Sturmgewehr 44 (assault rifle 44) with its intermediate round proved just how advantageous such a design really was, that the concept was validated. Interestingly, the StG.44 was first called a submachine gun by the Germans (Machine Pistol 44), and the AK-47 was first called a submachine gun by the Soviets and by NATO in the early years. It was during WW II that the German designation of “assault rifle” was coined, and it was such a captivating term it has come to nearly universal usage, referring to a hand-held weapon capable of semi-automatic or fully automatic (selective) fire, fed from a detachable box magazine, which fires an intermediate rifle cartridge. Earlier designs firing a full-size infantry round, such as the Fedorov, BAR or AVS-36, however, were still assault rifles as well — just as a Model T, although an early design, was still an automobile.

The weapons of mass destruction held by national powers today exist primarily to checkmate similar hostile weapons. We must continue to discourage their use. But if future wars involve the employment of tactical atomic weapons against military forces, a modern field army would see much of its sophisticated equipment reduced to shambles in a matter of minutes. When the dust settles on an atomic battlefield, to a great extent the outcome will still depend on small groups of desperate men, the assault riflemen.

Today’s emerging threats include antagonists with a suicide mentality so base it does not care if all parties lose, and they are more likely to employ asymmetrical warfare and individual terrorist operatives, or work for their goals within “low-intensity” conflicts. When such faceless combatants can be engaged, however, the fighters on both sides mostly comprise small units of individual riflemen, armed with what has become known as an assault rifle.

In addition to the military context, modern police fighting organized crime find their new adversary so well funded and equipped that police elements are increasingly forced to train and operate as paramilitary forces to combat “traditional” crime, in addition to their role in responding to terrorist threats at street level, with an assault rifle in their hands.

Assault rifle performance and technical characteristics are largely determined by the ammunition used. Designers have been aware of this fact for many years, but prior to the appearance of the German Sturmgewehr in the early 1940s, all standard military automatic and semiautomatic rifles were chambered to fire cartridges that previously had been used in older weapons. (One exception was the U.S. carbine’s .30 caliber, 7.62×33mm cartridge, which was not a true assault rifle cartridge.)

Design limitations imposed by older “full power” rifle cartridges made it impossible to develop truly lightweight rifles that would shoot effectively during full-automatic fire. Not only was mechanical functioning violent with such cartridges, but projectile dispersion was very great. Muzzle climb during burst fire was the usual result. After the first shot of the burst, subsequent ones generally passed harmlessly over the target, or in compensation, lateral dispersion increased.

As a first step in changing Western thinking about infantry ammunition, French armament engineer Marcel Devouges offered the following observations about ammunition for automatic weapons in 1924: “The cartridges for automatic arms (except pistols) were originally designed for non-automatic weapons, and for tactical concepts which have been greatly modified since the experiences of the last war.” He noted that during World War I, each army designed its machine guns for the same cartridge used in their service rifles.

Devouges commented that there was a growing opinion favoring separate cartridges for each class of weapon, because of the contrasting needs in today’s terms of the general-purpose machine gun, those of the squad automatic weapon, and those of the automatic rifle (self-loading rifles). General purpose machine guns were expected at the time to kill out to as far as 3,500 meters. Squad automatic weapons and automatic rifles would be employed against targets up to 800 meters. Devouges suggested that 7mm would be the optimum caliber for lightweight automatics, and that 7.5mm would be suitable for GPMGs. His ideas and suggestions were far ahead of contemporary thinking.

In actual practice, those nations that employed a single cartridge (7.62mm or larger) for rifles and machine guns retained that type ammunition through the end of World War II. Those countries that had calibers smaller than 7.62mm (generally those in the 6.5mm class) adopted a larger, more powerful caliber cartridge during the 1939-1945 conflict. Most notable in this latter group were the Dutch, Greeks, Italians, Japanese, Norwegians, Portuguese, and Swedes. Adoption of a second cartridge was usually related to the needs of the machine gun. In some instances — such as the Italian 8×59mmRB Breda cartridge and the 7.9×57R M.v.M. Dutch — the new ammunition was provided exclusively for machine guns.

As with the American decision to keep its Model 1906 .30 caliber (7.62×63mm) cartridge, and not adopt the proposed .276 Pedersen (7×53mm) ammunition, other industrialized nations opted to retain their older munitions because of the enormous expense involved in fielding a new round — even if they agreed to the reduction in power and range of the service rifle ammunition. In addition to research, development and tooling costs, huge quantities of ammunition must be stockpiled in peacetime in anticipation of wartime usage. For nations such as the United States and the former Soviet Union, which have large territories and global commitments of troops, ammunition also must be prepositioned worldwide. Allied and enemy experience with the unanticipated magnitude of cartridge expenditures during the World War led to cautious behavior in the post-1918 period. Nearly all belligerents had artillery shells and small arms ammunition shortages. For some, for example the Russians, these shortfalls were chronic and fatal.

During the final years of World War II, and in the immediate post-war period, all major armed forces examined the tactical advantages of switching to less bulky and lower power infantry ammunition types. The decade 1943-1953 was a period of much experimentation with new rifle cartridges. Many competing designs appeared, with a few key ones surviving testing and evaluation through to adoption,

Within alliance groupings, “interoperability” has become a priority. Standardization of ammunition and weapon types simplifies logistics involved in the field supply of large armies. It also requires more stringent attention to common standards and quality control. The Warsaw Pact armies were all very successful in standardizing both guns and cartridges, NATO allies have settled for a few standard types of interoperable ammunition that will work in a wide variety of weapons of the same caliber. In theory, all 7.62×51 mm NATO cartridges will function equally well in the Fabrique Nationale FAL, Heckler & Koch Gewehr 3 (G3), U.S. M14 rifles, and FN MAG, Rheinmetall MG3, Manufacture Nationale d’Armes de Saint Etienne (MAS) AAT 52, and U.S. M60 GPMGs, without concern about the country in which the weapon or ammunition was manufactured. As we shall see in subsequent discussion, this interoperable ideal is sometimes elusive. Weapons types respond differently to differnt cartridge case materials (e.g., brass vs. steel, material hardness) or to variations in chamber pressures or gas port pressures. Projectiles can respond significantly differently to even slight changes of barrel twist. The basic goal of interoperability is often difficult to attain.

Assault Rifle Operating Systems

Significant confusion and misunderstanding exists concerning the various operating systems of the world’s assault rifles (and other firearms). First it must be understood that all self-loading firearms are operated by expanding gases when the cartridge is fired, and are thus gas operated. It is how these gases are harnessed that more precisely defines the operating system. Although new operating and locking systems have continued to evolve over the years, the definitions of operating systems described below are based on those established by the late Colonel George M. Chinn, USMC (Retired). These systems are listed in Col. Chinn’s book, The Machine Gun, Volume IV, Parts X and XI, published by the Bureau of Ordnance, U.S. Navy.

  1. Blowback: An unlocked bolt opening by the opposite reaction of a cartridge case when the projectile travels forward. Blowback bolts depend on being relatively heavy to delay opening until pressure has dropped to a safe level, and thus are sometimes called an “inertially locked breech.” Although a blowback action can sometimes assist another operating system, the only assault rifle to use the simple blowback operating system was the Burton.
  2. Delayed Blowback: An operating system beginning with a fully locked breech being unlocked shortly after the cartridge is fired through a recoiling part, the movement of a primer, or another means of unlocking. No assault rifle using this system was ever mass-produced. Often confused with retarded blowback operation.
  3. Retarded Blowback: A system of operation beginning with a semi-locked breech that is opened by the opposite reaction of a cartridge case being fired, but only after overcoming a retardation caused by a mechanical means, usually a combination of leverage and spring tension. Examples of retarded blowback assault rifles include the German G3 and the French FAMAS. Often confused with delayed blowback operation.
  4. Long Stroke Gas Piston: A locked breech mechanism operated by a gas piston that travels a distance at least equal to the length of the cartridge being fired. Examples include the WWII German FG42, MP44, and Stoner 63.
  5. Short Stroke Gas Piston: A locked breech mechanism operated by a gas piston that travels a distance less than the length of the cartridge being fired. Examples include the U.S. M1 Carbine, M14 rifle, and the Steyr AUG.
  6. Long Stroke Piston and Cylinder Via Direct Gas: A locked breech mechanism operated by a gas, piston and cylinder that travel a distance at least equal to the length of the cartridge. Examples of this system include the AR-10 and M16 rifles where the bolt (piston) and the carrier (cylinder) are actuated by direct gas fed through a tube from the gas block.
  7. Short Recoil: A locked breech mechanism where the barrel and bolt recoil together for a distance shorter than the length of the cartridge before being mechanically unlocked, allowing the bolt to continue rearward while the barrel returns forward under spring pressure. An example is the Johnson assault rifle.

Assault Rifle Locking Systems

  1. Rotating Bolt: A locking system where the bolt rotates to bring two or more locking lugs into engagement with counterparts in the receiver or extension of the barrel. Examples include the AK-47, M14, and M16 assault rifles.
  2. Tilting, or Propped Bolt: A locking system where one end of the bolt is tilted to lock into a recess in the receiver of the rifle (usually the rear of the bolt). Examples include the MP44, and FN-FAL assault rifles.
  3. Toggle Lock: A locking system where an arm attached to the bolt is cammed into a recess in the receiver to lock the bolt. An example of this system was used in the U.S. Browning Automatic Rifle (BAR).
  4. Locking Tabs: A locking system where two locking tabs (or lugs) are forced out from the bolt into locking recesses in the receiver. An example of this system was used in the British EM-2 assault rifle and was also used in the WWII German G43 rifle.
  5. Locking Block: A locking system where a block or wedge is forced into a recess or recesses in the bolt to lock it to the receiver. An example of this system is found in the Czech VZ58 assault rifle.
  6. Roller-Delay: A semi-locking system where roller-like lugs are forced out into rounded recesses in the receiver or barrel extension, and held there by a combination of leverage in the form of a wedge-shaped mass and spring pressure. Examples are the German G3 and the Swiss SG510 assault rifle series.
  7. Roller Lock: A locking system similar to Roller-Delay, except that the rollers are mechanically locked into their recesses and are unlocked when an operating rod moves the mechanical lock. An example is the SIG 530 assault rifle.
  8. Rocking-Lever: In this locking system a lever connects and bolt and bolt carrier and forces them into battery with leverage under pressure of the recoil spring while pivoting against a shoulder in the receiver. When fired, the cartridge case exerts pressure on the bolt, which in turn pushes against the carrier. This in turn forces the rocking lever out of engagement with the receiver to unlock the breech. This system is found in the retarded blow-back operated French FAMAS assault rifle, where the delay lever also acts an accelerator to add velocity to the bolt group.
  9. Rising Chamber: In this system the chamber is a separate cylinder that moves up and down into and out of battery within the receiver. This system is found in the Stoner and Steyr Advanced Combat Rifles (ACR).
  10. Rotating Chamber: In this system the chamber rotates into and out of alignment with the bore. The rotating chamber system is used in the German G11 assault rifle.
  11. Lockless Chamber: In this system the chamber and breech are integral with the barrel and neither move during operation. Instead, the cartridge is inserted through a side port, and the solid end of the barrel acts as the breech block with a separate means of sealing off escaping gas. The McDonald Douglas Advanced Combat Rifle uses the lockless system.

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