

It’s not really worth it. A lot more complexity for the trigger and firing mechanisms, barrel alignment; etc. Weight is also a concern with any carry weapon. There were a couple of weapons in history that tried a dual mag setup
MP40I
The Burton
AF2011 (More double barrel but does fire simultaneously)
There’s also the DIY jungle style
coupled magazines, refers to detachable box magazines, and thereof, that are fixed together side by side, for example, with tape, or purpose made magazine clamps, also called magazine couplers. The spare magazine may be pointing downwards in relation to the one fitted to the weapon, as to keep the feeding lips clear for insertion into the weapon.
In general these days, belt fed weapons are used for more capacity where needed.






Note, the designation is
MP40/Inot1:P May help your research.