MP-40/I: The Dual-Magazine Experimental MP-40


The MP40/I was an experimental modification of the MP-40 submachine gun developed by the Erma company (we think) in late 1942. It was presumably developed in response to complaints of Soviet fire superiority with SMGs because of their large drum magazines (and also the larger number of SMGs used by the Soviet forces compared to German units).

The concept is a pretty simple one – the regular magazine housing was replaced by a much wider housing with a sliding block that held two separate standard magazines. One of the two magazines would always be positioned where it could feed and fire, and when that magazine was empty the shooter could simply slide the block to one side and move the second (still full) magazine into position to fire. The prevented the need to fish around in a slow magazine pouch to find a new magazine when a reload was needed.

However, there were several disadvantages to the dual magazine system. For one thing, an MP-40 with two full magazines hanging off it becomes quite the heavy and poorly-balanced weapon to handle and carry. The additional open areas required for the sliding block were much more prone to gather dirt and foul than the standard gun, and the extra weight on the relatively thin receiver tube often contributed to creases or other damage to the magazine well and ejection port areas of the gun, rendering them unusable.

Only a small number of these guns were ever made (around the middle of 1943), and very, very few survive today. They were originally matched to the serial number of the base gun, but this example is mismatched (although the magazine itself is authentic and original).


  1. Strikes me as a way around 5 round magazine limits, maybe with a lever action to advance the magazine cluster to next full one.

      • At the risk of stirring things up, could an extension of this line of thought (i.e. separate, horizontally sliding magazines being a way around a 5 shot limit):

        Could something along the lines of a Lewis gun magazine actually be considered a cluster of small magazines, being rapidly shuttled horizontally, feeding only the top round each time (remember, we are only talking about magazine capacity, not order or sequence of rounds selected for firing)? If the actual feed lips are in the gun, and not the magazine, would it be very different from simply shuttling the two magazines back and forth for the featured MP-40/I, only feeding the top round each time? If such a firearm existed, would it be considered to have either

        1) Two separate magazines, feeding separately, or

        2) A double stack/double feed magazine, with the rounds contained in two separate housings?


    • “drum magazine for it”
      It is easier to carry several stick magazine rather than drum magazine. Also drum magazines tends to need more effort during loading, more that proportionally to its capacity.
      Also designing properly working drum magazines is not easiest task, especially making reasonably priced one. Notice that during WWII generally sub-machine guns evolved magazines evolved from drum (if such was applied) to stick.

      • True.If they wanted to increase capacity they could also have tried a 4 stack magazine as well.No gun modification necessary.

        • Exactly. Any if you have (say) six 30 round stick magazines (180 rounds), versus three 60 round drum magazines, you have double the chance of a defective or damaged magazine with the drums, rendering inaccessible twice as much ammo.

          Good point Cherndog

      • According to the Osprey book on the MP38/40 family

        by the time Erma had developed this lashup, the Russians had dropped production of the 71-round Suomi-type drum for the PPSh-41, and had gone entirely to the 35-round curved “stick” magazine, because the 71-round was a PITA to make, unbalanced the gun, and was a PITA to keep
        functioning correctly in the field, under any conditions.

        And oh yes, like the Thompson drums (L and C), the rounds “sloshed” back and forth as you moved, which gave away your position to Germans with itchy trigger fingers.



    • Emp44 also has two part bolt and firing pin which is also more complicated than it needs to be.
      Maybe it was really intended as some kind of tank/apc mounted firearm where additional weight and problems of mag switching mechanism would be lessened compared to when used out in the field.

  2. The slight reverb off of the tile gives Ian a golf-announcer like slightly breathy narration.

    “Hauptmann Schmidt seems to be having some trouble addressing the ball. He’s trying to play over a rather difficult lie here on the 16th hole at Stalingrad.”


    • Ha – perfect

      “It’s the Cinderella story. The crowd is standing on it’s feet. It’s about a 400 yard shot. He takes out his 9 iron…”

      Or approximation thereof 😉


  3. Actually, soldiers armed with this SMG supposed to use normally just one magazine and to use another only in critical situations. Such situations are CQB or fighting off Soviet mass assaults. In situations like that there’s just not enough time for replacing empty magazine with another one from a pouch.

Leave a Reply

Your email address will not be published.