Following military trials, especially historical ones, is a wonderful way to learn what not to do for weapons design. While some trails produce a few good offerings like the Garand/Pederson trials, most tend to quickly weed out the inferior designs (like the MHS’s rapid dropping of the Remington RP9 pistol). And sometimes, those trails can pick one of the bad ones… like Italy did with their Breda Modello 30, their LMG going into World War 2.
Almost immediately one notes issues with any design that includes an oiler to help with extraction from the chamber. While this can be done well (look to the Japanese machine gun designs of the same era), the inclusion was just a band-aid over an overall terrible design.
Externally the most obvious issue is the choice for the permanent magazine to be open to the environment. As just about any modicum of experience with firearms design will tell you – its much easier to keep crud out of a weapon than it is to try and deal with it once in the action. Open magazines just invite debris to enter the gun. This issue adds insult to injury with the reloading technique, which has the permanent magazine pivot forward to accept a stripper clip of ammo which is difficult to top off as four rounds will remain fed into the weapon yet not retained.
Gun Jesus, aka Ian from Forgotten Weapons, goes into extreme detail with one Breda Modello 30, showing its shortcomings en-masse. It’s an entertaining expose if only to see what not to do with a machine gun.