Thompson SMG in 30 Carbine (Video)

When the US military released a request for what would become the M1 Carbine in 1940, the Auto-Ordnance Corporation offered up a Thompson submachine gun simply rechambered for the new .30 Carbine cartridge. This entailed a new magazine, a receiver modified for the longer magazine, and a new barrel and bolt face – but the other Thompson parts could remain unchanged form the standard .45 ACP models. This made the submission a pretty cheap and easy effort for Auto-Ordnance…which is a good thing, considering that it was almost assured to be rejected.

The stipulations for the new carbine included a weigh requirement of 5 pounds, and the Thompson weighed more than double that (in both .45ACP and .30 Carbine forms). Only a few were made, and the one submitted for military testing was rejected outright on the basis of weight. This example is serial number 1, and resides at the Cody Firearms Museum.


  1. Nice video Ian, I think the National Firearms Collection in Leeds, England has a 30 Carbine Thompson too but I’m not sure. They do have several BSA built Thompson’s in various calibers though. They are radically different from a standard M1928 model though in that they are ‘rifle’ like in so much as they have a rifle type grip and trigger as opposed to a pistol grip!

    • The Ruger New Model Blackhawk in .30 Carbine has a 7.5 inch barrel, which probably is long enough to tame the worst blast. Not that I actually know, since the cartridge is not actually popular around here.

        • .30 Carbine primer is Small rifle
          .357 Magnum primer is Small pistol, magnum
          Notice that generally primers intended for short-barrel fire-arms should activate powder faster (to effective harness length of barrel), than primers intended for long-barrel fire-arms.

      • Euroweasel, having had the opportunity to shoot a Ruger Blackhawk in .30 carbine with military ball I can assure you that the flash and blast is impressive.
        About like a 2″ .357 with plus P loads or a little worse.
        It’s a different matter with handloads tailored to the barrel length, it really shines a flat shooting small/medium game cartridge with those loadings.

        • “handloads”
          How does .30 Carbine headspace in that particular fire-arm? Revolver are generally using headspace/rim method but .30 Carbine is rimless. It headspace on mouth or some other method is?
          If you want handload wouldn’t be rimmed cartridge better choice, as it headspace on rim (overall length is not critical)?

          • Daweo,

            On the case mouth, same as any other rimless cartridge.

            Some early M1917 revolvers did not have a shoulder in the chamber and that caused problems with folks using .45 ACP loose, without half-moon clips. That was corrected in later production to properly function with loose rounds.

            There is a specification for case length that all ammunition should fall within, handloads or not, no matter the rim type.

          • “same as any other rimless cartridge”

            Should have said, “same as any other cartridge that headspaces on the case mouth” ^__^

            In other words, this revolver has a square shoulder at the front of the chamber that controls the forward movement of the cartridge. So, no roll crimp allowed, just like on most semi-auto pistol cartridges. Same rules apply that you would follow for semi-auto pistol reloading.

        • Yes, powder burn rate is also important. I worked up a .357 Magnum load with slow pistol powder for a Marlin lever-action. At a shoot on a friend’s farm folks were lining up after dark to shoot those (yes, I warned them those were handloads) from a snubby revolver, just to see the resulting ball of flame.

          • Not too many years ago, my dear sweety discovered the …shall we say…advantages….of the snub nosed revolver loaded with reloaded flashbangs.
            Take a youngish, tallish, cuteish, sweetie wiling to suffer a somewhat protracted exposure to “Gee, mister, can you help me with this big ole’ black ole’ boomer my boyfriend makes me hike around with?

            Things not always not so much what they seem, are they?

            Always wise to check six

  2. Wasn’t another major problem with the Thompson its cost? Seems to me, that was a major motivation in efforts to replace it.

    • Well that is obvious. Making another Thompson in 30 Carbine would also make a logistical nightmare, since parts were expensive to make. If memory serves well, the Thompson action is more or less pure blow-back with a forged receiver and bolt. Without a locking mechanism one could expect lots of incomplete cartridge combustion and powder burns on the off hand… or am I wrong?

    • “efforts to replace it”
      In fact after WWII broke out, it was noticed in USA that sub-machine is more useful weapon that it was considered to be. So purchases started, Thompson sub-machine gun was not lightest but was available, Reising sub-machine gun was not most reliable but it was available, U.S. Submachinegun, Caliber .45, M2 and United Defense M42 was developed using older but known manufacturing processes.

    • It’s also a sub machine gun, rather than a carbine. If that distinction was specified in the request, although apparently the M1 was originally intended to be select fire seemingly “an M1 smg, or select fire carbine” but this feature was omitted to speed up it’s development. What is the distinction between the two? Perhaps that a carbine was to have no facility for fully automatic fire and/or this was to be achieved via a closed bolt as oppose an open bolt used in smgs for increased accuracy from a carbine, or maybe length is a carbine longer than a smg. A proprietary cartridge the .45 Remington-Thompson was developed as a perceived improvement at the time- 1923, but not adopted which had an overall length of 1″ which doesn’t seem right as that’s shorter than the .45Acp, perhaps it means case the length which is more similar to a .30 Carbine. So perhaps they thought the 7.62x33mm would be a good smg cartridge discounting the carbine notion if that was distinct from a smg as aforementioned and tried to present that as a carbine, and the previous experience of making a Tommy gun in another calibre helped them make the transition. M2 select fire M1 carbines… Came out later. Maybe it would have been a good smg in .30 Cal, an smg if adopted that would have been better than a carbine and a .45Acp Smg. Although heavy, it probably was accurate. Info from Wikipedia.

      • “The stipulations for the new carbine included a weigh requirement of 5 pounds” Open bolt smgs out, closed bolt… Carbines, select fire or otherwise in. The distinction between carbine and smg then, was presumably was which position the bolt operated from.

        • This Thompson gun in .30 cal, select fire albeit from an open bolt might be considered an assault rifle then due to the cartridge as the Mkb42h fired from an open bolt. If the smg fired pistol cartridges. Classification conundrum. Goodnight he he.

          • Same weight the Mkb42h. Somewhat less potent of a cartridge… Still, more rifle than pistol. Beats .45Acp or 7.62x25mm so 9mm Luger also. Maybe it would have been quite good.

          • “conundrum”
            Sub-machine gun = weapon firing pistol cartridge
            Carbine = weapon with barrel shorter than rifle
            (both conditions are necessary but not sufficient)
            thus these are not mutually exclusive (weapon might be sub-machine gun and carbine at one time)

          • is: “(…)weapon firing pistol cartridge(…)”
            should be: “(…)weapon firing pistol cartridge and capable of full auto-fire(…)”

          • “it would have been quite good.”
            But when then they were searching for weapon to replace sidearms (i.e. M1911 automatic pistol) not for assault weapons.

          • Replacing pistols… Replacing rifles. For a PDW suitable for folk who didn’t need a full size rifle, but might struugle to defend themselves with a pistol.

        • Did they specify that this light rifle was to be a select fire weapon? Like it said on Wikipedia.

          If so why isn’t it an assault rifle.

          • Because the .30 US Carbine cartridge is classified with pistol cartridges. Assault rifles fire intermediate rifle cartridges, more powerful than pistol rounds but less powerful than traditional smokeless powder era rifle cartridges. If the M1 carbine had been chambered for a more powerful round, a select fire variant would qualify as an assault rifle.

      • Originally, they intended the M1 Carbine to be selective fire (original specs 1 Oct 1940, with first tests planned for 1 February 1941). This requirement was dropped in the development phase, *solely* because it was thought doing so would cut development time (even so, first tests weren’t run until May because of the other delays).

  3. Considering the scale American small arms production numbers during WWII, making the Thompson in .30 carbine Caliber would have simplified logistics of SMG with front line troops quite a bit. I presume the Thompson in .30 Carbine didn’t work very well.

    • Apparently Ordinance never tried it, so who knows how well it worked. Maybe Auto Ordinance submitted it with the idea that Ordinance would be so pleased with the functionality and durability of the gun that they would say, “forget the 30 carbine, we had what we needed in the Tommy Gun all along, just make more in 45.” Obviously did not happen, but that would be one explanation of why Auto Ordinance submitted it.

      • Imagine the logistic nightmare of a firearm that looks like a Tommy Gun, but doesn’t take Tommy Gun magazines or ammunition. Is it any wonder that the Powers That Be said, “Thanks, but No Thanks” ^__^

        The PTB just wanted a simpler and quicker to produce Tommy Gun, and eventually Savage Arms provided that with the M1 and M1A1.

        • White Rifle? Does that use the same gas piston principle that was eventually incorporated into the M14 rifle and M60 GPMG? Interesting history.

          I appreciate White’s persistence in sending his 1929-31 rifle into the 1940 trials, but obviously his .276 rifle would get rejected by the US Army as completely unsuitable for the light rifle specifications, which aside from caliber more importantly had to be light.

          The White Rifle ventilated handguard has a nice futuristic look to it, and certainly shows a more realistic appreciation for the heat generated by semi-auto fire than the semi-auto rifles which simply copied the wooden handguard fashion of bolt-action rifles.

    • No, adding a second.30 cartridge that is not compatible with the established standard.30 chambering makes logistical complications and problems. Since.45 was already the established standard pistol round, in the regular supply chain and could not be mistaken for the rifle cartridges it is not such a problem. If the new weapons were chambered for something like the old .345 Winchester devised for the Burton rifle, it would also have been less confusing logistically.

      • They could have just renamed it .31 carbine or something. This was commonly done with artillery ammunition, for example the British 77mm HV tank gun was named such to avoid confusion with the US 76mm tank gun ammunition. Both were actually 3″ or 76.2mm guns. The later US M40 106mm recoilless rifle was named such to avoid logistical confusion with 105mm howitzer ammunition.

      • Logistical complication? In practice the M1 carbine ended up sprinkled all over an US Army Rifle Company, and it fires the same cartridge as fired by the .30 Thompson in question.

        Pistol ammunition actually fired by pistols in WWII must have amounted to an insignificant drop in the bucket as far as small arms logistics is concerned. The only significant expenditure of .45 ACP ammunition would have been by fire from .45 caliber SMG types.

        That means actual ammunition expended by an Army Rifle Company during WWII required THREE different cartridges delivered all the way down to the squad level: .30 rifle, .30 carbine, and .45 pistol. If the Thompson SMG had been issued in .30 carbine caliber instead of .45 ACP that would have reduced the types of cartridges down to two.

        • Brad,

          The logistical problem wasn’t the availability of .30 Carbine ammo, it was that .45 cal. Tommy Guns were already in service with both ourselves and our allies. So, “Throw me a Tommy Gun magazine!” … “Which one, .30 or .45?” … “.30!” … “I don’t have any of the new ones. Anyone have some of those new .30 cal. Thompson mags?”

          Not a good idea at all, so rejected out of hand.

          • The question is purely academic, since the .30 caliber Thompson probably didn’t work very well.

            But if we assume that the .30 Thompson DID work and it WAS adapted, then wartime production of the Thompson SMG would have been in .30 carbine rather than .45 ACP. The very limited numbers of .45 Thompsons produced before 1940 could have been relegated to second line duties.

            Considering how much lighter .30 carbine ammunition is compared to .45 ACP, that would have been a blessing both to the Thompson gunners who had to carry it and the supply personnel who had to deliver that ammunition.

            (and really now, Allies? Do you really believe that mattered at all as far as US Army small arms logistics? If the US really had switched to .30 caliber Thompson production that would have made it even easier for the US to ship off older stocks of .45 caliber Thompsons to the UK than the US was already doing.)

          • Brad,

            I agree, the question is purely academic. The .45 ACP Tommy Gun and its ammunition was already developed, adopted, and in production before this prototype was produced.

          • On the other hand, did the US Army actually need a new cartridge for a defensive carbine meant for support troops? I don’t think it actually did. A carbine, either select fire or semi-auto only in .45 ACP would have been sufficient for the job. The main problem with pistols as self defense weapons is that they require much more training to master than shouldered weapons, especially if you want to hit anything beyond 25 yards. A .45 ACP carbine would easily have been effective up to 100 yards and probably even a bit farther, which in practice would have been enough for a PDW. If you design the carbine to be select fire, you can also replace the Thompson with a cheaper design early on.

        • That’s my point: the .30 carbine ammunition choice was a mistake from that point of view, regardless of what arm it was fired from.

        • Actually, no the rifle companies would still require the following small arms ammunition types: .30-06 ( belted), .30-06 ( en bloc clips), possibly.30-06 ( stripper clips), .30 Carbine and .45 ACP for a dozen pistols or so. Possibly some 12 gauge as well. This doesn’t address the various mixes of AP, Ball, Tracer and Grenade Throwing rounds. Avoiding.30 Carbine completely could reduce the logistics load, however. One less cartridge type, in exchange for larger quantities of .45 for the SMGs, with the weight penalty of the heavier ammunition. And no, dropping sidearms wasn’t in the cards either. Issue of pistols ( including revolvers) became more widespread in all the major armies throughout the 20th century.

    • “Useless POS can’t even shoot a sniveling gun-less Kraut without blowing up in my hands!!!” Many guys hated the M3 for not being made to last in the field.

      • The grease guns were issued to tank crews and such into the 1980’s. They were in National Guard armories up into the 1990’s. I do not know much about them, but I had not heard before that they had a problem coming apart.

        Actually, it seems like folding-stock Reisings would have been ideal for issuing as last-ditch weapons to tank crews.

      • “without blowing up in my hands”
        I know that early Grease Gun have its flaws and thus M3A1 variant was developed:
        but I am not aware of self-destruction.
        I found choice of double-column-single-feed magazine unfortunate, as it is more pesky to load with cartridges than double-feed.
        Also I suspect that hypothetical will have either very high RateOfFire or either be very heavy.

      • The problems with the M3 were bending of the ratchet lever that cocked the bolt and accidentally denting the receiver enough to jam the bolt. Otherwise it was exceptional for reliable function. The single feed magazines were a pain. And someone bent on machinegunning unarmed prisoners has questionable judgement and needs to be disarmed anyway!

          • Even them. I recognize it happened and would again under similar circumstances. That does not excuse it! What right do we have to claim moral high ground if we do not enforce it on ourselves? We , each and every one of us, must hold ourselves to a higher standard. And demand the same in our own. Forgive the preaching, but 20 years wearing badge have only re-enforced that belief.

    • Carlos Lastufka,

      Thanks for that link. Always interesting to see what’s in the Springfield Armory Museum. Too bad they didn’t retain the paperwork.

  4. Sadly the Pattern Room ( now the NFC ) does not have a 0.30 carbine Thompson or any of the BSA ones in 9mm,all five of the
    BSA guns are in the USA.
    It does however have a Savage made TSMG 1928 in aluminium alloy

  5. I wonder how bad it would climb with a long burst. I’d expect it would be pretty bad in a .30 carbine chambered 1928 model.

    • I’ve dumped a mag in a full auto M1 which was possibly an M2 or a modified M1 it was the most smooth weapon I fired in full auto, didn’t even wobble a line of empties just burst upwards in what seemed a constant stream instantly until it stopped. Out the lot, the M1 Garand and that carbine were the best auto/semi of the selection which included an Aksu an SLR, Romanian AKM of similar weapon varieties for comfort. The SLR was something of a shock stood up, never having fired anything other than 5.56mm in a rifle, at the time.

    • .30 Carbine has a much lighter projectile and muzzle climb depends largely on the recoil impulse, so while it is be impossible to make any kind of exact prediction, I would expect a 1928 in .30 Carbine to be quite similar to one in.45 ACP, perhaps slightly worse.

    • The Thompson is completely controllable in full-auto mode. Any climb that results during firing is the result of inexperience or improper technique on the part of the shooter.

  6. A 30 Carbine Thompson is an interesting weapon. I don’t have a Thompson, but I do have an M1 Carbine and a Ruger Blackhawk in 30 carbine. Both are fun to shot. The Thompson weighs 16 pounds and for comparison the M1 Garand is 10 pounds. I would hate to lug that thing in the field, but the .45ACP is an excellent round for close quarters where the Thompson was designed to operate. Lots of stories about how the M1 Carbine did not perform in WW II and Korea, but a lot of that is the small bullet that cannot expand.

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