This is an overall explanation of the weapons on the Mastadon.
More specifically it refers to the size of them, which is repeatedly drawn into question.
The Mastadon has particularly powerful railguns on it, they match up to the power of the Mammoth Tank easily.
Railgun technology is quite complex and requires a lot of electro-magnets, wiring and powercells in order to work. The Mammoth Tank has very long barrels to fit all this required tech in but the Mastadon has had to have it all compressed into 2 chin mounted cannon. This is why the weapons are so bulky looking. They have to compensate for the shorter length in order to keep the power behind the shot.
It may seem a little too realistic to go into that much depth but that's one of the aspects I'm attempting to keep in.
hope you done soon