After a five-year search U.S. SOCOM (Special Operations Command) has selected a new PDW (Personal Defense Weapon, or pistol replacement) for special operations troops or any personnel needing a compact weapon more powerful than a pistol. The new PDW is the Sig Sauer MCX Rattler, which was already available and did not require development of a new weapon. SOCOM wanted a PDW that used the 5.56mm ammo as American assault rifles and could have an assault rifle stock as an attachment. More importantly the MCX could use the new (2011) subsonic (low-velocity) 7.62×35mm Blackout round by swapping out the standard 5.56mm barrel assembly. The Blackout round could use M4/M16 magazines and, with the addition of a suppressor (silencer), provided MCX users with very quiet weapons, especially when firing single shots. The Blackout round was adopted by several European countries for their special operations forces. The MCX Rattler is 584mm (23 inches) long, 204mm (8 inches) high, and weighs 2.7 kg (5.1 pounds) with a 30-round magazine, and normally uses the Blackout round with the 5.56mm round as an option.
The war on terror after 2001 caused many changes and one of the less well-known ones was the large number of new weapons designs that appeared. One of the more interesting, but generally unnoticed areas of developments is the PDW, which first appeared in the 1980s when NATO sought a smaller and more compact replacement for 9mm machine-pistols. The 9mm round was the most widely used pistol round ever. Police forces worldwide used the 9mm machine-pistol/submachinegun, as do paramilitary and military forces for non-combat and security troops. And special operations troops found PDWs useful, as did some types of police. PDWs never became a large seller but there was demand for weapons manufacturers to introduce new models and demand and new technology developed. By the 1990s new models demonstrated how compact, lightweight and powerful machine pistols or PDW could be.
For example, the Russian PP-2000 PDW uses a 9x19mm round. The PP-2200 weighs 1.4 kg (3.1 pounds), has a 183mm (7.2 inch) long barrel and can use 20 or 40 round double stack (short) magazines. It has a folding stock so it can be used like a pistol or a submachine gun. You can attach a red dot sight and light (to the bottom). When folded up in “pistol” mode it will fit in a jacket.
After 2001 the growing threat of terrorist attacks led to a proliferation of PDW designs, some using different ammunition. In 2010 the Rock River Arms PPS (Performance Piston System) Pistol appeared. This was a 5.56mm weapon that used a new internal design. It has a short gas piston, with the recoil spring and guide rod over the 21cm (8 inch) barrel. The entire weapon, which does not have a stock, was 44.5cm (17.5 inches) long and weighed 2.2 kg (5 pounds). There were single shot and full automatic versions, each costing $1,335. There have been some notable European PDW designs from the major pistol manufacturers like H&K and Sig Sauer.
If you want a smaller PDW, you often have to go with smaller ammunition. An example of this is a 2009 Chinese PDW design that used a 4.6x30mm round. This weapon is a variant of the Type 79 compact submachine gun which uses the old Russian 7.62x25mm round. The 2009 Chinese weapon weighs 1.6 kg (3.6 pounds) and has a 30 round, dual stack, magazine. Rate of fire is single, 400 or 600 rounds per minute. It has a Picatinny rail on top for scopes and sights. With the telescopic stock closed, the weapon is 34cm (13.4 inches) long, and 54cm (21.2 inches) with the stock extended. The weapon is gas operated with a closed bolt. The bullets are about half the weight of 5.56mm ones and the 4.6mm round is lethal at short ranges, especially in bursts. The bullet travels at high speed (over 700 meters a second). The 4.6mm round will not penetrate walls or ceilings as well as 9mm or 5.56mm bullets, meaning less chance of unintended casualties.
The Personal Defense Weapon never really succeeded, on a large scale, as a pistol replacement. The military, especially in the United States, simply developed an M-16 with a shorter barrel and stock (the M-4). Many troops who previously only had a pistol, now had an M-4. These were cheaper than PDWs, and not much larger. But security professionals, especially bodyguards, are a growing market for the easily concealed PDWs. Many police departments use them for special situations.