The Heckler & Koch HK MP5 submachine gun is currently used by most of the world's elite special forces groups. Introduced in the 1970s, the weapon was designed as a compact system to be used in confined areas and firing the widely-accepted 9x19mm Parabellum pistol cartridge. The 9mm cartridge has a lower lethal knockdown value with a minimal range from 70 meters (230ft) to 200 meters (656ft) though a proven intermediate manstopper nonetheless. Models of the MP5 series feature a muzzle velocity of 1,312 feet per second (400 m/s). Comparatively, the AR-15-based American M4 Carbine fires the 5.56x45mm cartridge and can reach out to 500 meters with lethal hitting power at a muzzle velocity of 2,970 feet per second (910 m/s). However, the major drawback of the firearm is its overall length in terms of the tight confines of urban warfare. What is needed, therefore, is a hybrid design set between the submachine gun and the carbine assault weapon.
A personal defense weapon (PDW) is a compact semi-or fully-automatic firearm comparable to a submachine gun. A forerunner to the modern PDW was the 1942 M1 Carbine issued to American airborne troops and had a unit price of $45 with a low muzzle velocity of 1,950fps while using a pistol cartridge. The M1 Carbine filled a role in World War 2 for officers and second-echelon troops such as truck drivers, engineers, medics and MP's who needed a compact weapon that could be removed from vehicles for quick-reacting personal defense.
C. Reed Knight founded the privately-held Knight's Armament Company (KAC) of Titusville, Florida in 1982. In 2006, his concern began work on a new firearms design recognized simply as the "Personal Defense Weapon" (PDW). The design was centered around a new 6x35mm cartridge with increased lethal ballistics at range and then developing the weapon to fire it. Knight's development of the 6x35mm cartridge was accomplished by optimizing the performance of the cartridge case, the bullet and the gun itself. The purpose of the new 6x35mm round was performance when using shorter rifled barrels. KAC could have built a weapon with a 12" or 14" barrel length and simply used the 5.56x45mm cartridge for the role, however, the selected concept was instead to go more compact and use an 8" or 10" barrel while still maintaining the desired effects at out to 300 meters. The KAC PDW was purposely designed to look and feel like the competing M4 Carbine to provide transitioning to the PDW as simple as possible. By making the trigger mechanism and the pistol grip the same as the M4, operating the PDW would feel the same, the weapon just more compact and lighter in the hold.
For 8" or 10" barrels one required heaver ammunition for the required range. To compensate for this, KAC selected a 65 grain bullet. The 65 grain is of the Open Tip Match (OTM) type bullet with a weight of 4.2grams, able to penetrate bullet proof glass and body armor out to 300 meters. This round also provides very little recoil, even at full automatic fire, allowing for good target acquisition and accuracy in subsequent shots - a major enhancement over the existing M4. Estimates suggest that the KAC PDW has some 75% less recoil than the 5.56x45mm NATO-chambered M4A1 Carbine. Those that have already fired the KAC weapon have likened its felt action to firing a pellet rifle. The PDW essentially attempts to tie assault rifle performance with the profile of a submachine gun while presenting minimal recoil - the best of all worlds.
Hornady Corporation exclusively manufactures the short .243 cartridge for Knight's Armament. As the cartridge is wholly unique to the PDW, it requires the receiver-magazine well section of the weapon to be 1/3-inch shorter than the magazine elements found on the M4. The 6x35mm cartridge is also .32-inches shorter than that of the 5.56x45mm NATO cartridge.
When the .243 caliber cartridge is fired from the 10-inch barreled PDW, it sends the 65 grain bullet out at 2,425 feet per second with a remarkable energy rate of 848 feet per pound. Compared to the 5.56x45mm NATO bullet fired from the same barrel length, the PDW 6x35mm cartridge has an additional punch of 74 feet per pounds of energy. This provides the PDW with a rifle-caliber cartridge through a compact and lightweight body favoring many shooters. The powder in the 6x35mm cartage is designed to burn completely in the 8- or 10-inch barrel so the operator will not see a huge fireball at the end of the muzzle nor hear a loud percussion sound. The PDW is concealable and compact as its length is made controllable through a folding stock realizing an overall length of just 17.5 inches (444.5mm) when folded - not being wider than a man's shoulder, the user can maneuver the PDW in tight spaces.
Several weight-saving measures have been incorporated into the finalized PDW: the folding butt-stock is skeletonized using less metal with no cover. The barrel is purposely short and has been expressly machined to be lighter. To reduce parts and weight, the bolt group is likened to the Kalashnikov though with fewer parts equaling less weight. The AK-style bolt group is almost completely confined in its secondary framework. The recoil spring is compact in the upper receiver. The muzzle break and the flash suppresser on the 8 inch and 10 inch barrels are tooled to accept a lightweight KAC sound suppressor.
The flash suppresser is one of the key components of the KAC PDW's design and based on an original Eugene Stoner creation providing very little recoil. The muzzle brake acts as a baffle to stop the rapid gasses created when the powder burns, pushing the bullet as it exits the barrel. As the gas thrusts against the baffle, it reduces the recoil while venting gas is driven out from 100 small exhaust holes around the entire brake. This reduces muzzle climb and reduces muzzle flash.
To a high degree, the PDW follows the M4/M16 pattern yet, because of the AK-style bolt group, there is no ejection port cover along the upper receiver group. The bolt is operated by two short-stroke gas pistons, each having a spring set in motion by two gas cylinders located on the side of the gas block. The fire control group is worth mentioning as it has three cross pins. Following the M16 configuration, the PDW has one for the trigger and the second in the hammer plus a third for the auto sear. To hold the pins in place, a retainer plate is used on the right side of the receiver. When the stock is folded it is held in place with a steel stud in the right side of the lower receiver group. The PDW has QD sling mounts right or left hand side as well as front and rear. The operator can choose a single sling point for concealment possibilities from three different locations.
The PDW has a number of standard rails that accommodate KAC systems plus other manufacturer's equipment. It utilizes a monolithic rail hand-guard arrangement using KAC's flip-up BUIS. The top rail can mount various optical systems as needed. Side rails are provided for different hand-guard panels, lights and laser aimers. The M16A2 pistol grip of the PDW has been reduced in length and made thinner.
For the past 20 years, weapons have been designed to fill the need for a smaller shoulder-fired system having a close to moderate range. With the production of the KAC PDW, elite forces and personal protection agencies will see the advantages of the PDW in a role long-held by the ubiquitous HK MP5.