Compact Machine Pistols (Personal Defence Weapons in current jargon) have a small but important role in military operations. They are intended to provide self protection for personnel who's role or burden prevents them from carrying rifles. They are also claimed to provide armament for units that must operate in civilian garb, but need more firepower than a pistol can provide. Many of these weapons are simply scaled down versions of standard sub-machine guns, and this does not always offer all of the features that a user needs. It is worth considering the design of such weapons in greater detail.
Obviously, the weapon should be small, and shaped so that there are no parts that will snag on clothing or equipment while it is being drawn.
A useful feature that very few designs have incorporated is a double action mechanism, so that the weapon can be brought into action as quickly as a conventional pistol.
The weapon must use an effective round. Often these weapons are used when in close proximity to an enemy, so a wound being fatal is less important than quickly incapacitating the target to prevent further hostile action. The current trend is to adopt very light high velocity bullets that give an impressive performance when tested against body armour. These rounds cannot be expected to have any useful level of stopping power. One tester described such ammo as having less effect than a .22 magnum round.(personal communication) This tendency may be compensated for by the high rate of fire some of these weapons have, but you have to wonder how effective it is to use a whole magazine on each target. Such light bullets are also unlikely to retain much energy down range, so will pose little hazard to rifle armed foes firing from beyond 100m. A better strategy (in this author's opinion) is to develop better APDS or APCR pistol rounds that can be mixed with FMJ or JHP ammo. Another technolgy that may be worth looking at is Abraham Flatau's Ring Airfoil bullets, marketed as “Ultramag” or “Cyclone” Preferably the weapon should be available in a .45ACP chambering.
The weapon should have a good forward grip to improve control. The folding grip used on the Beretta M93R pistol has much to recommend it for a weapon that has the magazine inserted in the grip. The gripable forward edge of the trigger guard used on the the Ruger MP9 is an alternate approach. A weapon with a forward mounted magazine should be capable of having this used as a grip. One of the advantages of the silencer used with the MAC-10/11 Ingrams was that is could be used as an add-on foregrip, so was often used even when covert firing was not needed. The muzzle brake effect of the silencer probably also helped control.
The weapon should have a good stock to assist in more deliberate shooting. If a retractable/folding type it should not get in the way when the weapon is carried holstered or concealed. The stock of the Ingram MAC10/11 was both folding and telescopic, and the folding part could be used as a rear stabilizing grip when the stock was not full extended. The stock of the Parker Hale IDW seems to have similar properties. A stock that can easily be detached as well as stowed has a lot to recommend it.
If chambered in a pistol calibre, it would be prudent to design the weapon to use the same magazines as the handgun the user is likely to be carrying. Since I first webbed this article (2001) a version of the Micro-Uzi using Glock pistol magazines has become available
The weapons should be capable of being suppressed to assist in covert operations, or when used as a hunting weapon by downed aircrew. For an aircrew PDW there may be some merit in having a small calibre weapon chambered in 22LR or 22WMRF.
Last, but by no means least, the weapon should be accurate when fired as a pistol and controllable when fired in fully automatic mode. Many ingenious strategies have been used to achieve the latter, as can be seen with weapons like the Steyr TMP, Parker Hale Bushman IDW and Finish Jati-matic, to name a few.
UPDATE In many magazine articles published on the P90 weapon and its round FN claim the SS190 penetrated 48 layers of kevlar at 200m, while the 9mm failed to penetrate 24 at 1m. This sounds impressive and is credible given the performance of the PSM ammo -notable, however, is they don't list what weapon the 9mm was fired from (though possibly I failed to copy it down). A P90 fired against a pistol would hardly be a fair comparison.
More interesting was the gelatin shooting data published.
The SS190 penetrates 5cm then tumbles and deposits all of its energy (495j/ 366.3ftlb) after 25cm penetration. It creates a 8cm diameter cavity -the implication is that this is a permanent cavity.
The 9mm FMJ, in comparison, exits after 30cm of penetration and only loses 97% (430j/ 318.2ftlb) and makes a 3.5cm hole.
My first reaction was that even if the bullet was spinning like a buzzsaw it was unlikely to make a unlikely to make a 8cm hole -the 5.7mm bullet can't be more than an inch long so to do this sort of permanent damage you'd need explosive expansion/fragmentation, which usually needs at least 2500fps of velocity -which this round is 200fps short of at the muzzle. Then I though about the Control here -the 9mm FMJ round used for comparison. A 9mm FMJ that delivers 97% of its energy in 12"? -and makes a hole nearly an inch and a half in diameter doing it! If FN have a 9mm hardball that can do this in flesh they needn't bother developing the SS190 -armies and police departments will be queuing up all the way back to the Drelandspoint! Whatever gelatin these were shot against isn't flesh analogue.
The pistol is slightly smaller than the M9 and much lighter, being mostly polymer (1.2 lbs). The magazine holds 20 rounds. I have fired several hundred rounds in one and would not miss it if I never fired it again. 22 mags do the same job and are cheaper and easier to produce. The 5.7 case is slightly larger in diameter and lacks the rim. About the same length, but the .22 appears slightly longer.
... PW: The power ratings quoted by FN are slightly more than a 9mm so I'm surprised by your comments -I'm not doubting you, understand, just surprised. ...
Actually, they don't come up to most 9mm performance Here are some samples:
9mm 115gr
1250fps
399 ft lbs
5.7mm 31gr
2346fps
379 ft lbs
.22 mag 33gr
2000fps
293 ft lbs
Our recent tests also show that mass is more important than energy calculated in this manner. Considering this, a 31gr projectile is an abysmal performer. Tests show it does no better than the slightly slower .22 mag in killing even small game.
The 4.6mm round of the HK MP7 is also likely to have very little "stopping power"
Further Thoughts If small calibre PDWs are to be of any practical use, they must combine a capability for accurate rapid fire with a large magazine capacity. The 50 rounds of the P90 or 40 of the MP7 are probably not sufficient for ammunition that will probably need at least 12-15 hits to do sufficient damage. Dino Snider suggests using a small calibre version of the four column magazine used in the Spectre MP. In his design another magazine would be stored in the forward pistol grip. I'm not sure if it is worth creating a new round, however. An existing round like the 22LR, 5.7mm SS190, 22mag or 4.5mm Interdynamics should be used instead. An interesting idea is a fully automatic version of the Calico 22. Another potential round (and one already in wide use) is the Russian 5.45x18mm PSM round. This has also been offered in a Stechkin type weapon, the Drotick.
The Grendel P-30 mangaged to carry 30 rounds of 22mag, so it should be possible to construct a selective fire 5.45mm pistol with more than the 24 rounds the Drotick carries.
