Compact Machine Pistols

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 whose 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 technology 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 grippable 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.
  

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 canot be more than an inch long so to do this sort of permanent damage you would 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 experimental 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 is not flesh analogue.

I’ll leave you with some highlights of a conversation with a friend who has extensively tested both the P90 and the Five seveN pistol:

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:

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 managed 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.

The .224 BOZ, using a 5.56mm rifle bullet in a 10mm Auto Pistol case also looks like a more sensible policy than the 5.7mm or 4.6mm.

See also Tanker Machine Pistols and PDWs

The above table compares a selection of weapons that might be used by a soldier for personal defence. A 22 magnum weapon is included for reference since its calibre, momentum and TKO are very similar to the 5.7mm and 4.6mm rounds. The 5.7mm and 4.6mm are spitzers, so would be expected to retain more of their original velocity downrange than a non-spitzer .22. However, the main requirement of a personal defence weapon is against close range aggression, so the round’s performance at near-muzzle velocities is more relevant. Sectional density gives us some indication of the rounds penetration and flight characteristics in absence of better data.

Momentum allows us to compare rounds of similar calibre. The higher the momentum the harder the target is hit.

The second value of TKO index gives a estimate that assumes the bullet is tumbling, as has been detailed here.

*Upper figure for 5.56mm would probably be higher since TKO does not model bullet fragmentation. Figures in brackets give TKO for a hollow-point round that mushrooms to 150% of original diameter.

A 42gr FMJ and 77gr subsonic round are available for the 4.6mm. If we assume a velocity around 2200fps for the 42gr and 1050fps for the subsonic round we still don’t see a TKO better than 4.75.

By the Author of the Scrapboard : Blog of the Books.
	Attack, Avoid, Survive: Essential Principles of Self Defence Available in Handy A5 and US Trade Formats. A5 Edition. US Trade Edition. New Global Edition Epub Global Edition Video Webpage
	Survival Weapons: Optimizing Your Arsenal
	Crash Combat Fourth Edition Epub edition Fourth Edition.
	Anatopismo: An Underrealm Novella
	Hell-Ay: Angel Town