Pete has a machine-gun with a large drum magazine (probably inspired by the famous Thompson Submachine gun/"Tommy Gun", popular with criminals, police and military forces in the era), but the barrel passes through the centre of the disc of the drum mag, which makes no sense mechanically (and looks bizarre). In any gun with a drum mag, the barrel feeds from the outside edge of the disc-shaped drum, not the centre (which holds no cartridges, making such a mounting-point impossible).