The submachinegun, as a class of small arms, is little over a century old as of 2026. Created to fulfill a need for fast, overwhelming firepower within the close confines of the trench systems of World War I, the submachinegun is generally a means of giving the individual a high volume of fire in a compact package. The submachine gun was unlike any other weapon before it. This characteristic of a large volume of fire in a small package has maintained the weapon’s value in close-combat situations, the modern equivalent of trench warfare. The use of pistol-caliber ammunition also makes the submachinegun of value to Law Enforcement for the weapon’s lower chance of over-penetration when fired with standard ammunition.
Basically, the submachine gun is a lightweight weapon, capable of full automatic fire, and being controllably fired by one man from the shoulder or hip. It stands out from other automatic weapons because of one of its defining characteristics of being chambered for pistol caliber ammunition.
Automatic fire means that the weapon will continue to fire for as long as the trigger is held back and there is ammunition in the feed system. The rate of automatic fire is referred to as the ‘Cyclic” rate and is usually expressed in Rounds per Minute (RPM). The cyclic rate is how fast the weapons will function from round-to-round. How quickly it can mechanically function. There is also a practical rate of fire. This is determined by the size of the ammunition supply in the feed system, and how quickly fresh ammunition can be reloaded. It also takes into consideration the cooling of the weapon, how long it will take to overheat. And the ability of the shooter to keep the weapon on target.
If the weapon is capable of semiautomatic fire, one round fired for each pull of the trigger, then it has a second practical rate of fire. This rate is partially determined by how quickly magazines can be changed as well as how much ammunition they hold. It is also considered to be aimed fire and so is considerably slower than full automatic fire. For practical purposes here, the semiautomatic rate of fire is limited to two magazines or less. For full automatic fire, the ROF is three, or rarely 4, magazines. In the case of large capacity feed devices, such as drums, the ROF is usually based on one or two such devices
The classic definition of a submachinegun includes:
The ability to be hand or shoulder fired effectively.
A large magazine capacity, 20 to 30 rounds minimum.
Capable of full automatic fire
Chambered for pistol caliber ammunition
Additional factors in a submachineguns design are:
Lightweight.
Simple and relatively inexpensive to manufacture when compared to other weapons.
OPERATING SYSTEMS
Open Bolt
Most submachineguns fire from the open-bolt position both for simplicity and cooling. In the open-bolt system, the breech bolt is drawn back against the mainspring until it is held by the sear. This cocks the weapon for firing. When the trigger is pulled, the sear releases the bolt and it moves forward under pressure from the expanding mainspring. The bolt strips a round of ammunition from the feed system and feeds it into the chamber. When the bolt closes the breech, the chambered cartridge is fired.
The act of firing drives the bolt back against the mainspring from the pressure of the propellant gases and the recoil of the bullet. As the bolt moves rearward, the fired cartridge case is extracted from the chamber and ejected from the weapon. The bolt continues moving until it reaches its maximum backwards limit, compressing the mainspring. Then the bolt moves forward, repeating the firing cycle as long as the trigger is pulled and there is ammunition in the feed system.
The open-bolt design is simple. Generally, it is only the weight and inertia of the bolt, combined with the pressure of the mainspring that holds the breech closed while the bullet leaves the barrel and the chamber pressure reaches safe levels.
The open-bolt system also leaves the breech open when the weapon is not firing. This allows for air circulation to help cool the breech and barrel. This design also greatly cuts back on the possibility of “cook-off,” a consistent problem with automatic weapons. Cook-off is where a round fires unintentionally from the excess heat built up in the barrel and chamber from a long period of firing.
A drawback of the open bolt is that the bolt can be moved unintentionally. This can happen when the weapon is dropped and strikes the ground on the rear part of the receiver. Also, an operator can cause an accidental discharge of the weapon when jumping from the back of a truck. If the weapon is jarred hard enough, the inertia of the bolt is overcome by the movement, allowing it to move back against the mainspring far enough for it to strip a round out of the feed system, but not moving far enough to be caught by the sear. In that situation, the bolt can be forced forward by the mainspring, chambering and firing the round unintentionally.
Closed Bolt
The closed-bolt design is generally more complicated than the open-bolt weapon. The breech remains shut in the forward position, holding a round in the chamber. Then a striker or hammer system moves the firing pin and firing the round. The design is also more susceptible to cooking-off a chambered round from excess heat after extensive firing.
The primary advantage of the closed-bolt design is the lack of bolt movement at the moment of firing. Instead of the jarring bolt movement of an open bolt system, the smoother closed bolt has a greater probability of a first-round hit and generally is a more accurate weapon. This accuracy is of particular importance in Law Enforcement as well as in some counter-terrorist actions.
A disadvantage of the closed-bolt system is that the weapon normally requires a locking or retarding system to keep the bolt from opening while the barrel pressure is too high. This normally means a more complicated operating mechanism and trigger group.
OPERATING PRINCIPLES
Blowback
Blowback is the simplest and most common operating system for submachineguns. Since most pistol ammunition has straight-sided cartridge cases, the blowback system works particularly well with them. In the system, the cartridge case acts as a piston when fired. The propellant cases drive the casing rearwards against the resistance of the bolt. While the propellant gases move the relatively light bullet down the barrel, they also act against the much greater resistance from the inertia of the heavy bolt and strong mainspring. The drawback with the blowback system is that it requires a fairly heavy bolt and/or a heavy mainspring in order to work effectively. The system also does not work well with high pressure rounds or with bottlenecked cartridges such as those fired from rifles. With an open-bolt design, the forward-moving heavy bolt is usually jarring to the operator, preventing a high degree of accuracy.
Advance Primer Ignition
As a means to lower the weight of the breechblock, while maintaining the simplicity of the blowback system, is the advanced primer ignition (API) principle. In the API system, the cartridge is ignited just prior to the bolt reaching the fully closed/forward position. This action forces the pressure of the firing cartridge to first overcome the inertia of the forward travelling bolt before it can move backwards. Then the chamber pressure forces the bolt rearwards, as in simple blowback. What this system of operation does is allow for a relatively light bolt to safely function in what is otherwise a straight blowback system. The tolerances for the operation of an API system requires exact mechanical timing for when the primer of the chambering round is fired. It has to be close enough so that the round is almost fully chambered as it is firing. If the round is fired before it is close to chambering, the pressure of the burning propellant gases can rupture the cartridge case, possibly damaging the weapon as well as injuring the operator. The point of ignition can be close, as little as under a half-millimeter in some weapons that use the API system.
Example – Sterling L2A3
Retarded Blowback
The retarded or delayed blowback system is fairly new for use in submachineguns. In the system, the weapon fires from the closed-bolt position. The energy for operation still comes from the pressures used in blowback, but the force is also used to overcome a retarding system before the cartridge begins to leave the chamber. In the most common, roller locked, retarding system (as used in the MP5 family) a pair of rollers help hold the bolt in the closed position. For the bolt to move rearwards, the rollers act against a pair of angled surfaces in the breech area of the receiver. The rollers have to act at a mechanical disadvantage in order to push the bolt away from the operating rod. Once they have moved back into the body of the operating rod, the remaining pressure in the chamber can force the bolt to the rear, continuing the action of firing. Extraction, the removing of the fired cartridge from the chamber, is particularly violent with this system. To prevent the head of the cartridge being torn off from the force of extraction, the chamber of the weapon has fine flutes cut in it. These flutes allow a small portion of the propellant gases to lift the sides of the cartridge case away from the wall of the chamber. Effectively “floating” a portion of the cartridge case on a layer of gas. The fluting also leaves the fired cartridge case marked with longitudinal lines, indicating exactly what kind of weapon ejected it.
Example – MP5 series.
AMMUNITION FEED SYSTEMS
One of the characteristics of the submachinegun is that it holds a large supply of ammunition. This gives the weapon a reasonable period of firing. However, many of the larger feeding devices are either complicated to use, maintain, and construct, or simply too long for convenient use. The most common feed device is the box magazine, a relatively simple sheet-metal box, in some cases plastic, that holds a row of ammunition in a column. The column of cartridges are pushed into position by a follower. The follower is a platform moved along by the pressure of a spring. Single-column magazines hold relatively few cartridges for their size and are rarely seen used in submachineguns. To increase the number of cartridges held in the magazine, they can either be staggered into multiple columns, or the magazine can be extended in length. A problem with the longer box magazines is that the follower spring cannot lift the heavy column of ammunition easily and usually needs a special tool to compress the spring as the cartridges are loaded.
Double Column, Double feed
In a double column magazine, the columns of cartridges are stacked in a zig-zag pattern. This increases the number of rounds that can be held in a magazine that is only slightly thicker than a single-column magazine, but still of a size that it can be easily held in one hand. When feeding the rounds into the chamber, the bolt strips ammunition from either side of the feed lips as the firing progresses. The most effective of the double-column designs is one of the earliest, the box magazines used with the Thompson submachineguns. The Thompson magazines are simple to load without tools the rounds being pressed down with the thumb until it rolls under the feed lips of the magazine.
Many double column submachinegun magazines use a feed system that holds the ammunition in a zig-zag double column. But the rounds are forced inwards by the sides of the magazine when they reach the point of being fed into the weapon. This system makes the feeding of the cartridge into the chamber easier as each round is in the same position for firing. The system also makes the magazines more sensitive to the condition and shape of the feed lips that guide the cartridge into position. The double column, single feed system also can require a separate loading tool to force the cartridges into the magazine.
Examples – MP 38 & 40, M3 & M3A1, Sten series.
Quadruple Column, Single feed
This is a relatively rare magazine that holds the ammunition in two staggered columns, each separated from the other by a metal sheet. The rising ammunition is guided in by both the followers and the formed sides of the magazine body to the usual single feed point. This style of magazine holds a maximum amount of ammunition in a reasonably sized box. But it is also complex and exacting to make as well as being somewhat more easily damaged.
Examples – Carl Gustave M45b (50 round box), Spectre M4
Drum
The drum magazine is one of the first types used in a true submachinegun, and is also one of the most difficult to make. In the MP 18/I, the magazine used was a complex drum magazine, originally designed for the Luger pistol. This magazine was a weak point in the design and was quickly replaced in post WWI Germany with a simple box magazine. The drum magazine does offer a large ammunition capacity carried in a relatively small space. The most successful drum magazine design was used with the Suomi designs. These drums were so effective that the Soviet Union held up issuing the PPsH-41 until its drum magazine had been perfected.
The drums hold the ammunition in a spiral column around the inside of the body. Often the cartridges are driven by a multi-armed star-shaped wheel that is powered by a clockwork spring in the center of the drum. When the ammunition is loaded in place and the cover of the drum secured, the clockwork spring is turned a given number of times (often marked on the outside of the drum) to power the star wheel. The drawback of the drum is that it is usually noisy as the ammunition can rattle when the weapon is carried. They are also heavy, but this is considered secondary because of the amount of ammunition that can be conveniently carried.
Examples – Thompson M1921 & M1928A1, Suomi Model 1932, PPsH-41
SUBMACHINEGUN GENERATIONS
First Generation
The first generation of submachinegun designs are characterized by being large hand-held weapons resembling thick-barreled carbines. Generally, they had wooden stocks and were built almost totally with carefully machined parts. The manufacture of such weapons was expensive and time-consuming compared to later generations. They tended to be mechanically complex and heavy for their purpose. This generation submachineguns were among the first of the weapons class and designed during World War I. They reached their pinnacle internationally during the 1930s though the manufacture of some of the designs continued through World War II.
The second generation of submachineguns was developed shortly prior to World War II. During that war, second generation weapons reached their most popular time with millions of them being produced all over the world. The distinctive characteristic of the second generation of submachine guns was that they were designed for newer mass-production methods. Stamped sheet metal and welds replaced machined receivers. Hard plastics such as Bakelite replaced wooden stocks and grips. Bolts, barrels, and such still had to be machined but even these could be made more simply with open tolerances allowing easier manufacture. Stocks were made to a folding or collapsing design to make the weapons more compact for carry and use in vehicles. Simplified design also increased reliability. Second generation submachineguns were also among the first to be seen with suppressors incorporated into their design.
The third generation of submachineguns were developed soon after World War II. These designs included stamped, folded, and welded sheet metal as their primary manufacturing method. Inclusion of plastics as grips and front stocks was also increased. Shoulder stocks were primarily metal folding designs. One of the most distinctive characteristics of third generation designs is their use of a telescoping bolt. In this type of bolt, much of the mass is forward of the breech face, surrounding the barrel. This allows for a more compact overall design while still having enough mass in the bolt to use simple blowback as an operating system.
Examples – Uzi family, Ingram family, Z-84
Fourth Generation
The newest generation of submachinegun are relatively few in number. These are more complex weapons with the capability of firing from a closed-bolt for accuracy. Manufacturing methods continue to use stamped sheet metal with an increase in die-cast plastics as furniture such as stocks and grips. In some designs, the entire receiver has been formed from plastic. Internal parts have also been made of plastic for use where they are not exposed to high heat.
Examples – MP5 series, P90, Kriss, Spectre M4
Machine Pistols
In Europe and elsewhere submachineguns are referred to as “Machine Pistols” from their earliest inception. The term Submachinegun, or Submachine gun, as applied to an automatic weapon using pistol-caliber ammunition, was first coined by retired Brigadier General John Taliaferro Thompson, primary designer for the Thompson submachinegun. In Europe, the term Machine Pistol also centered on the weapon’s use of pistol caliber ammunition. But there is another type of weapon that has its name confused with this designation.
A true “Machine Pistol” is more specifically a handgun capable of full automatic fire. These are relatively rare designs due to their difficulty to fire controllably and accurately on full automatic fire. For this reason, many true machine pistols are fitted with a removable stock. There are a few submachineguns that include a folding stock, but are so compact that they can be referred to as machine pistols. Semiautomatic pistols that have the capability of full automatic fire, and have a separate stock available are still considered handguns.
Examples – Jati-Matic, PP63, KEDR, Micro-Uzi
Personal Defense Weapons
The newest style of submachine is the PDW, or personal defense weapon. These are very compact submachineguns that can be shoulder fired as they have some form of stock. The intent of such a weapon is to give a user the means to defend himself when his normal duties prevent him from easily carrying a full-sized weapon. These users include vehicle drivers, pilots, heavy weapon crewmen, and communications technicians, among others. The PDW allows these personnel to have a weapon immediately available that has a greater volume of fire than a pistol, yet is compact enough to carry on their person while continuing their duties. Generally, the PDW is also easier to train an individual to use accurately that the more training-time intensive use of a handgun.
