What-if SMG for late 1930s and on

The essence of a machine carbine (to use the British army nomenclature) is automatic fire with a pistol cartridge. Open bolt blow back is simple and effective for the task and the 9x25 cartridge as strong as will work thus. The Tokarev copied the smaller diameter Mauser 25mm cartridge but principally as it allowed the same barrel machinery as the Moisin Nagano bolt action rifle. Once you start getting into delayed actions and closed bolt firing you are shading off into making a short, weak rifle. The MP5 is such. A fine weapon for it’s task, but not a true sub machine gun I would submit.

Like the bicycle, the true sub machine gun is a mature design. One can fiddle about with the details but the simple open bolt blow back full automatic fire from a pistol cartridge remains the basis.

Drum magazines have died out for good reasons. Box magazines have vastly improved from the very early days and the Sterling is an exemplary example. More rounds is more weight and the box magazine has to be carried and extracted/reinserted into the soldier’s webbing pouch or similar and this limits length. Cunning design might get a four stack ‘coffin’ 50 round magazine but I doubt if there is enough gain over a 35ish round reliable strong double stack one to justify the expense, weight on the gun and complexity.

As a universal sub machine gun I would take the Sterling as my model but in 9x25 with a long and a short version with modern sights and modern materials to reduce weight whilst maintaining reliability and robustness. If you want a small carbine then go to a short assault rifle.

The inexperienced look at sub machine gun accuracy by comparing shot to shot with a carbine. This misses the point. The sub machine gun is for short bursts. The target being rapidly reaquired for the next short burst. It is whether the burst group contains the target that counts. When you need quick suppression then it is rate/duration of fire that counts. I am of the opinion that many sub machine guns have too rapid a rate of fire. Partly to limit weapon size and weight by limiting the mass of the bolt. I am in favour of accepting a heavier bolt for the return of a lower rate of fire. Telescoping bolts allows one to reduce the receiver length and is useful in making the gun very short but a classic bolt puts the reciprocating mass rearwards which, in shoulder stock form, reduces the shaking of the gun as the mass works back and forth on firing each round.. M any years ago I tried a Sterling with an early both eyes open red dot as well as the ordinary open sights. The red dot was infinitely superior in all ways so there is room to benefit from simple modern sights over open ones.

I can see no reason for a sub machine gun to have a single round setting. Many types have been initially made with the option and had it removed in later production but I know of no example where it was absent and added later on. It is a (sub) machine gun. Pull the trigger and it goes ‘dakka’. I can see why a police user would want it as a warning of intent.

Remember. We want a strong sub machine gun not a weak rifle.
 
The best handgun round available in the 30s was arguably .357 Magnun. Make a rimless .357 round and offer it in a decent SMG and you have a great weapon.
If you want a SMG with an existing auto pistol round but with a bit more range than 9mmP, the choices are not much, you have 9 and 7,63 Mauser (and it's 7,62 soviet cousin), 9mm Largo and .38 Super.
If you want something more powerful go wild and use the rounds created for the Mars pistol. If 8,5x26 Mars is not powerful enough for you, you need a rifle...
A Suomi in 8,5 Mars would be as close as you can get to an assault rifle without leaving SMG territory.
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Mars pistol cartridges: from left to right, .45 Short Mars, .45 Long Mars, .360 Mars (aka 9mmMars), and 8.5mm Mars (aka .335 Mars)
Images from wiki (Suomi) and from this site (Mars Ammo) https://www.forgottenweapons.com/early-automatic-pistols/gabbett-fairfax-mars/
 
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BSA had a licence to build the Kiraly designed Hungarian SMG in 9x25 mauser export. Value engineer this gun for mass production in 1939 and make plenty of hot ammo and you are good to go. BSA originally costed the gun at £5 each, this cost could probably have halved if mass produced.
 
If someone hits a man sized target firing a single round from a Thompson
M1928 had a nice ladder rear sight, and can verify could get you on target at the 200 yard range without much trouble.
Still 'Minute of Man' grouping.
With an M1 Tommy? Look for dirt clumps popping and adjust like you would a spraying a hose.
 
Telescoping bolts allows one to reduce the receiver length and is useful in making the gun very short but a classic bolt puts the reciprocating mass rearwards which, in shoulder stock form, reduces the shaking of the gun as the mass works back and forth on firing each round..
Back to the Winchester 1907, that does acts like a blowback telescoping bolt, has much weight forward, in the charging rod.
 
You can make 351 Winchester self-loading by starting with 357 Mag brass, and time on a lathe.
In Metric speak, its 9X35mm semirimmed, 1900J energy with 12g bullet at 570m/s
In Infantry speak, it's perfect:cool:
But 1900j put's you in assault rifle territory. For SMG uses I'd rather have .357 Magnun nunbers, around 1000j at around 500m/s with a 8g bullet. The 8,5 Mars gave 100j at 470m/s with a 9g bullet.
 
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I am kind of wondering if we are aiming for too powerful a round here? Most guns that use even the 9x25mm (such as the Danuvia 45M) seem to be near the weight of a rifle. If you are looking for a light gun that you can use at short range (which seems more the profile of an SMG) I kind of think the 9x19mm or similar was probably the right choice for most militaries.
 
M1928 had a nice ladder rear sight, and can verify could get you on target at the 200 yard range without much trouble.
Still 'Minute of Man' grouping.
With an M1 Tommy? Look for dirt clumps popping and adjust like you would a spraying a hose.
Interesting thanks. In the context of this thread, in a world where the typical service rifle was a bolt action service rifle firing a full power cartridge I can potentially see some nations seeing value in such a sub machine gun.
 
I am kind of wondering if we are aiming for too powerful a round here? Most guns that use even the 9x25mm (such as the Danuvia 45M) seem to be near the weight of a rifle. If you are looking for a light gun that you can use at short range (which seems more the profile of an SMG) I kind of think the 9x19mm or similar was probably the right choice for most militaries.
You need the extra power for useful range if you want to replace rifles. If you want to use a mix of rifles and SMG and you stay with convencional rounds you have to rely on the rifle caliber weapons for most of the over 100m work.
In WW2 the Soviets did just that, and relied in team work between LMG, rifles and SMG to provide firepower at all ranges.
 
The OP also indicated that post ww2 developments could be taken advantage of, so I suppose a something along the lines of the MP5 firing an optimized cartridge, used by well trained soldiers who perhaps could be expected to deal with adjusting a sight for use beyond say 100 meters (perhaps often but not always in semi auto ?) is a possibility. On the other hand something along the lines of an Uzi or a Sterling might also be attractive to some.

As already noted the role of the submachinegun largely fell to assault rifles after WWII. While spec ops units still use outstanding examples like the MP5 et al, whichever gun selected needs to be (a) rugged, (b) reliable, (c) reasonably priced, (d) retains at least one unique trait that helps it endure [like modularity for use of multiple types of ammunition], and (e) remains effective to 150m to 200m. The latter makes me wonder if 7.62x25mm Tokarev is not automatically the cartilridge of choice despite candidate guns like the Type 80 Norinco, which if modernized and its barrel extended (ideally with a larger magazine and getting rid of the overheating-causes-rounds-to-fire quirk), might be worth considering.


I suppose if modern tech is some how made available then something with an action along the lines of the G11 or perhaps the AN94 that could fire short bursts at a very high cyclic rate with a single recoil impulse (to the operator) might have a niche role in WW2 and could be technically considered to be an SMG if it fired suitable ammunition.

I realize that assault rifles firing intermediate cartridges are probably a better investment for most nations than expensive optimized SMG's, but this thread is about optimized SMGs :)

And that is a niche area of firearms these days. If we stay more modern there should be a reason such a weapon sees widespread adoption and/or retention.
 
You need the extra power for useful range if you want to replace rifles. If you want to use a mix of rifles and SMG and you stay with convencional rounds you have to rely on the rifle caliber weapons for most of the over 100m work.
In WW2 the Soviets did just that, and relied in team work between LMG, rifles and SMG to provide firepower at all ranges.
Yep.. Windage at longer ranges is also likely to be an issue for typical pistol based SMG's at longer ranges.
 
There is a need to replace the bolt-action rifles, however asking from SMGs to do that all by themselves is a bit too much. Especially if we want to make millions (or at least hundreds of thousands) in just a few years. So I'd suggest to keep the power of cartridge under a leash.
IMO, the .30 Carbine cartridge in a SMG mechanism (= no positive breech lock) is probably the upper limit before the gun weight, size, 'producibility' and price make the combination a worse bet than it was the case with the OTL SMGs. At 1300J, it seems like the upper limit for a ~.30 round; even that is almost twice the muzzle energy of the 7.62X25 round when fired from a SMG. Probably a happy medium of ~1000J for .30 rounds would've ticked all the boxes wrt. effective range, all while keeping the weight, size and price/producibility favorable.
 
There is a need to replace the bolt-action rifles, however asking from SMGs to do that all by themselves is a bit too much. Especially if we want to make millions (or at least hundreds of thousands) in just a few years. So I'd suggest to keep the power of cartridge under a leash.
IMO, the .30 Carbine cartridge in a SMG mechanism (= no positive breech lock) is probably the upper limit before the gun weight, size, 'producibility' and price make the combination a worse bet than it was the case with the OTL SMGs. At 1300J, it seems like the upper limit for a ~.30 round; even that is almost twice the muzzle energy of the 7.62X25 round when fired from a SMG. Probably a happy medium of ~1000J for .30 rounds would've ticked all the boxes wrt. effective range, all while keeping the weight, size and price/producibility favorable.

Like I said at the beginning a two (or more) track approach seems helpful to me (especially before intermediate cartridges, assault rifles, semi auto service rifles firing full power cartridges etc become available.)

Maybe a mass issue open bolt design (probably firing a typical handgun cartridge) and a more limited issue closed bolt design (perhaps firing an optimized cartridge to try stretch the practical range beyond 100 meters.) The idea of a red dot style sight also makes sense if that tech can be made available in WW2.

Once armies get their hands on assault rifles or perhaps semi auto rifles firing full power cartridges I suspect they may loose interest in closed bolt SMGs in this notional time line. Or just stick with open bolt SMG's firing hand gun cartridges and focus on developing semi auto service rifles, intermediate cartridges, assault rifles etc..
 

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Yep.. Windage at longer ranges is also likely to be an issue for typical pistol based SMG's at longer ranges.
Pistol rounds have a variety of issues at range. Probably the largest of them is simply the shape of the bullet which is all about maximizing mass of the bullet whle keeping the over length of the round (i.e. cartridge cast and bullet for fold who aren't gun fluent) to a reasonable length, this is especially the case for auto pistol rounds. This results in a rounded nose, rather stubby, less than ideally aerodynamic bullet. This is very much not the case for rifle bullets dating back to before WW I

As examples
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9mm FM Jpistol bullet

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7.62mm FMJ Rifle bullet

As you can see the 7.62mm rifle bullet has a considerably different shape, both in the tip, and also in the overall shape and length/width ratio. This results in a much higher velocity and muzzle enegy which tends to translate directly to maximum range. It is possible to create a pistol round with the spitzer point/boattail design, but these are very rare (currently the 5.7mmx28 is gaining a lot of interest, but it is very much a post 2000 design).

Subguns tend to use typical pistol rounds and generally have shorter barrel lengths than even assault rifle which also had an impact on both range and accuracy, although this last point can vary depending individual weapon design.

Images are both from the Midway.com website.
 
Now that we're at small calibers.
The 5.7mmx28 and .22 WMR are probably at the low end, with muzzle energies between 410-530J. Higher powered bracket is populated by the intermediate cartridges of Western and Easter prominence, with ME of 1400-1900J, with the 5.45mmx39 being the with the lowest energy there. So we'd probably want again a 1000J cartridge for our SMG? Such a cartridge exists in the 1920s in form of .22 Hornet, but for a SMG we'd probably prefer a rimless version of it. The .22 Spitfire, designed by Johnson by necking-down the .30 carbine is/was also at ~1000J.

Going with such cartridges might offer superior ballistics over the 'classic' SMG cartridges with muzzle velocities of 800 m/s from barrel lengths we expect on SMGs. The savings in weight of both weapons and ammo carried should also be felt by the grunts.
To the best of my knowledge, apart from USA, Germany was also making the training rifles in .22 LR in some quantities between the wars - important to ramp-up since the barrel-making equipment is already there.
 
To the best of my knowledge, apart from USA, Germany was also making the training rifles in .22 LR in some quantities between the wars - important to ramp-up since the barrel-making equipment is already there.
The British converted SMLE's and P14's to .22 LR as the Rifle No.2 and Rifle No.3 respectively.

As far as ammo selection I would recommend using something that is also suitable your standard service pistol. That was a major logistical benefit of SMG's, and it would be a shame to have to run three streams of ammunition when you can run two.
 
The British converted SMLE's and P14's to .22 LR as the Rifle No.2 and Rifle No.3 respectively.
Thank you.

As far as ammo selection I would recommend using something that is also suitable your standard service pistol. That was a major logistical benefit of SMG's, and it would be a shame to have to run three streams of ammunition when you can run two.

Americans and Japanese used 3 ammo types in ww2 for small/infantry arms, Germans were introducing the 3rd ammo type by 1943/44, Italians used 3 ammo types and almost introduced the 4th (7.35). Both Germans and Italians also used the .32 ACP. Both Italians and Janaese used also the British .303 in aircraft. British used one ammo type on Enfield revolver, another on Browning HP, and the classic .303; add the 7.92mm for Besa.
Seems like that only Soviets used 2 ammo types, with 3rd in pipeline by the end of ww2.

But then - cut down the .223 Rem into the .22 TCM and there is a cartridge that also can offer close to 1000J, while also suitable for pistols. Reminds me to the 7.62x25 further necked-down.
 
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