<XMP><BODY></xmp>Compact MPs

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.

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.

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:

9mm 115gr 1250 fps 399 ft lbs
5.7mm 31gr 2346 fps 379 ft lbs
.22 mag 33gr 2000 fps 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.

5.45mm Drotick
More on 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.

Grendel P-30
Grendel

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


Weapon Bullet wt (gr) V0 (fps) E0 (ftlb) SDMomentum (ftlb/sec)TKO
FN P90 5.7mm3123453780.080.322.33 - 4.66
HK MP7 4.6mm 24.7 2379 312 0.11 0.261.52 - 3.04
22 magnum rifle4019103200.110.34 2.4
M16 5.56mm623100 1323 0.177 0.85 6.15 - 12.08*
9mm Pistol12412003970.140.667.55 (11.32)
.45 Pistol2308503690.162 0.8612.56 (18.85)

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.

More on PDWs

By the Author of the Scrapboard :


Attack, Avoid, Survive: Essential Principles of Self Defence

Available in Handy A5 and US Trade Formats.


Crash Combat Fourth Edition
Epub edition Fourth Edition.
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