What is the recoil of a submachine gun like, and why so few calibers

So if submachine guns were created in WW1 and heavy machine guns were created before WW1, why did it take until WW2 to create fully automatic portable rifles? I thought the StG in Germany was the first portable fully auto rifle.

It was largely inertia. Infantry rifles were seen mostly as aimed fire weapons, whereas fully automatic fire is more of a suppressive field or mass firing weapon. Also, soldiers were generally firing 7mm or .30 caliber rifles, and carrying enough ammunition (on top of all of the other heavy kit they had to ruck) to make fully automatic fire a reality just wasn’t very practical. The handful of full bore .30 caliber infantry rifles like the FN FAL, Browning M1918 Automatic Rifle, and the M14 were rarely actually used in full auto mode as infantry weapons, either being adapted as light machine guns or generally used in semi-automatic mode.

The Soviets (and Chinese who licensed their designs) went with an intermediate power round with the 7.63x39mm, but both East and West forces eventually moved to light powered rounds like the 5.45x39mm and 5.56x45mm NATO which allowed soldiers to carry twice or more the amount of ammo and magazines with higher capacity, and that actually had better terminal ballistics within their ranges of engagement.

Submachineguns have a different role for use in relatively close quarters and so fully automatic or burst fire makes more sense in the expectation that the soldiers firing them may not have time to take careful aim and are generally not front line infantry where longer range fire is necessary.


It took until about WWII for the people who establish weapons requirements to realize that intermediate power cartridges are sufficient. This, because the vast majority of infantry to infantry fighting happens within 300-400 meters. Even the StG had to be snuck past Hitler because he didn’t want to sacrifice range.

Without acceptance of intermediate power cartridge, you either use low-power rounds and have insufficient range to reach 300-400 meters or you use high-power rounds which have too much recoil for burst fire in your average rifle.

If they’d realized/accepted what the requirements should be earlier, they could have made assault rifles way back in the 1880s with the advent of smokeless powder. Even today’s assault rifles are usually used in semi-auto anyway.

Thrust is a measure of force, which might be in newtons or pounds. Consider an M2 Browning with a 700 gr Barnes round firing 600 rounds per minute. In reasonable units, that’s a 0.045 kg/bullet with 908 m/s exit velocity and 10 bullets/s. Multiplied through, that’s 409 N, or 92 lbs.

Of course, you aren’t going to be walking around with an M2 anyway, so talk of “leaning into it” is somewhat moot.

That poster claimed the average recoil force of a machinegun was 50lbs. Unless the poster meant “a specific machinegun”, rather than “the average machinegune”, then 50lbs is much too high. It is especially high considering the thread is supposed to be about submachineguns.

Plus, painstaking analysis of war experience pointed out that most infantry combat takes place under 300 meters, and most of that under 100 meters. Most of the bolt-action rifles used in WWI/WWII had effective ranges around 1000 meters, and were intended for formation volley firing in a way eerily reminiscent of Civil War combat, only at 600 yards. Once upon a time, I had an officer’s handbook from the 1920s that detailed how to direct volley fire from troops onto targets, how to estimate range, etc… The authors of the book weren’t expecting infantry combat inside of 300 meters with individually aimed shots.

So the intermediate cartridge made sense, even without going full-auto. They were lighter (could carry more), easier to cycle through a weapon (don’t kick so hard, were shorter in length), and at typical combat ranges, were just as effective.

Really the weirder situation was why it took SO long for most armies to go to a self-loading rifle. The US and USSR were the only two nations to have fielded a self-loading rifle at the start of WWII with the M1 Garand and SVT-40 rifles. The Russians didn’t equip all formations with SVT-40s though, with lots of older Mosin-Nagants and various submachine guns (PPSH-41, PPS-43, etc…) being pressed into service during the war. Other nations like the UK never did actually field a self-loading rifle until long after the war (FAL in 1957).

Interestingly, the Russians didn’t start out with intermediate cartridges (7.62x39) with the AK-47; they originally started with the SKS Carbine in that caliber, and moved to the AK shortly thereafter.

Depends what you mean by ‘automatic portable rifles’. BAR, obviously, stands for Browning Automatic Rifle, though in WWI the M1918 was more often referred to as the Browning Machine Rifle. In any case it was a WWI ‘rifle’ that could fire full automatic, as was the French CSRG aka Chauchat an earlier and less highly thought of weapon of similar concept. Though both were ‘squad automatic weapons’ in later terminology, not a general issue rifle for each soldier. But if calling those ‘automatic rifles’, they were much more widely used in WWI than SMG’s were. Even the BAR was actually used in WWI in about the same small numbers as the German MP 18 (estimated 3,000 MP 18’s reached the front, BAR’s equipped at least 4 AEF divisions in the closing weeks of the war which would also be around 3,000), v around 1/4 million Chauchat’s. The somewhat odd Italian twin barrel bipod mounted Villar Peroso SMG was used earlier than the MP 18 but not in really large numbers either.

If you mean a general issue rifle capable of automatic fire the Russian Fedorov Avtomat say limited use in WWI, weighing not much more than a normal bolt action rifle. The two issues with weapons like that were:
a) creating an economical to produce weapon at that weight that was reliable and maintainable in battlefield conditions, and once that was solved
b) full caliber, full power ‘automatic rifles’ light enought to be used as general issue weapons, in terms of carrying them around, tend to have too much recoil energy to be manageable on full automatic. IOW a BAR is pretty manageable on full auto with .30 M2 ammo because it’s too heavy to be a general issue rifle.

The German solution the Soviets emulated was a shorter less powerful ‘full caliber’ cartridge to create a more practical general issue automatic rifle (Stg.44 then AK-47). At first Western armies post WWII had the idea of simply firing cartridges almost as powerful as WWII rifle cartridges (eg. 7.62mm NATO) from rifles about the same weight. But the M14 and FN-FAL aren’t that manageable on automatic and were not often used that way in service. The follow on idea in West was Small Caliber High Velocity first adopted with 5.56mm in the AR15 (as designated when adopted by the USAF in 1962, later designated M16 by the army, subsequently Colt recycled the name ‘AR15’ to refer to civilian semi auto versions, so many people now think that’s the only thing it refers to). The Soviets eventually came around to that idea with the 5.45mm versions of the AK from the 1970’s. Some people still debate of course how often it’s tactically useful to fire even relatively low recoil SCHV rifles on full auto.

Maybe **Napier **just wanted to contrast submachine guns vs. “real” machine guns. Average thrust is one reason why the latter tend to have bi/tripods.

I don’t know how to define “average” across the entire space of machine guns (Do we include the M134 Minigun? That might drive up the average a tad), so I just picked an M2 as a common example. An M240 has a thrust of ~28 lbs; less than 50 lbs, certainly, but I wouldn’t say much less. It’s within a factor of 2.

We still had M3A1s in service when I was a wee tank platoon leader.* They were part of the normal equipment for the M60A3 which did not go out of service until the mid 9. There were racks to hold two of them to supplement the crew’s pistols when dismounted.** Now I never got a chance to fire it myself. Every time we had the extra ammo to conduct a familiarization fire I somehow ended up running the M16 range. Overwhelmingly, the troops I knew who had just fired it complained about it being hard to control. That is not a comparison to the Thompson or MP40 but it is rare either are talked

They were light, cheap*** and quick to make, though. I would not discount the propaganda angle for the claims in your cite.

  • Some continued in service with my battalion until after 9/11. They also fit in the holder on our M88 recovery vehicles so we kept some even after we transitioned to the Abrams. We went to war and somebody suddenly realized that the M88 vehicle crew already carried M16s and maybe we could just leave the holder empty.
    ** [shudders]Death before dismount!
    *** Really cheap. The replacement price on the property book when we finally turned the last ones in was a little over $30 dollars, IIRC. I was the battalion logistics officer at the time and my section NCO and I were joking about claiming we lost all of them and filling out the statement of charges to pay for them. Not that we could have gotten away with simply losing a bunch of weapons. Don’t mess with the fantasy. :stuck_out_tongue:

Although thrust is a measurement of force, what is really pertinent here is impulse; that is, the force distributed over unit time. How the impulse is mediated depends on the mass of the gun and any muzzle brake or buffer systems. The reason that machineguns are mounted on bipods (or more rarely tripods, which you only see with heavy machineguns) isn’t to reduce recoil but to permit the shooter to maintain greater accuracy and a wider range of fire in a prone or squat position with a weapon that is generally too heavy to hold out in front for a long duration.


I think that, at a minimum, we should restrict it to unmounted machineguns that are designed to be actually fired by a person from a standing position. Otherwise, using the term “lean in to” is meaningless. A minigun has zero perceived recoil for the person shooting it. Because it’s securely mounted to the vehicle. A mounted M2 recoils when you shoot it, but it’s mostly just a dull, thumpy shaking. It’s not what one normally considers as recoil–it doesn’t push back on the shooter. And it certainly doesn’t require the shooter to “lean into it”.

… in a thread about the recoil of submachinguns.

Right. As mentioned upthread, in the countries that had the 7.65 pistol cartridges as a common service handgun load (e.g. USSR up to WW2), SMGs were made for that ammunition while that was the case, but they moved on when other standards were adopted.

The same standardization issue is why sales of SMGs in .40S&W, 10mm or .357SIG, would not be that great relative to 9mm and .45.

Having actually fired all three within the time span of about 25 minutes, I can safely say that the Thompson was heavy, but solid and easy to control. (seems to be a theme with US early WWII-era weaponry). The MP-40 was not particularly ergonomic- skinny grips, etc… but easy enough to control.

The M3A1 (the one with the finger-hole in the bolt) was a different story- it was hard to control, and at best, just sprayed rounds downrange. My guess is that it was fairly light and fired a relatively powerful pistol cartridge, so in comparison to the Thompson, it was a bit wild.

The STEN on the other hand was even simpler and rougher in construction, but since the 9mm was less powerful, was surprisingly controllable and accurate. Astoundingly so if you considered how sketchy it looks.

I wouldn’t 100% discount it, but personally would tend to mainly discount it. There aren’t training films showing how, for example the 75mm in M4 tanks was really so much more effective v German tanks’ armor than 7.5 or 8.8cm German tank guns v the M4’s armor…because it obviously wasn’t. I take that film to showcase a favorable aspect of a US weapon which was true, at least for some shooters.

The M3 (8.2lbs empty) was only slightly lighter than the MP40 (8.8) or Thompson (~10.5 for apparent M1928A1 in that film). Using this calculator to rough it, the recoil impulse, recoil velocity and recoil energy of M3 firing M1911 .45cal were 1.27 lb-sec/4.99 ft/sec/3.18 ft-lb. The Thompson firing same ammo to slightly higher mv, 1.29/3.94/2.54. The MP40 assuming 115 grain 9mmx19 .94/3.67/1.84. So MP40 lower per shot, but also note the very slow cyclic rate of the M3 in that film. And the recoil energy of an M1 rifle is in the low 20’s so all three SMG’s have quite low recoil comparatively.

Were we at the same range, because I did just those three in Las Vegas one trip.

After the introduction of the M16A1 but before the introduction of the M16A2 the US Army performed a lot of testing. One test was on the effectiveness of full auto fire. The test involved M16A1 rifles, life size silhouette targets, very high speed cameras, and other necessary items. 4 varients of the test were performed.

  1. 1 round fired semi auto. 100% of these rounds hit the target.
  2. 2 rounds fired full auto. 100% of the first rounds and 74% of the second rounds hit the target.
  3. 3 rounds fired full auto. 100% of the first rounds, 74% of the second rounds, and 23% of the third rounds hit the target.
  4. 4 rounds fired full auto. 0% of the fourth rounds hit the target.

So, the M16A2 came out with 3-round burst and no full auto option