why dont the machine guns shoot like machine guns?

[Ancient Seraph]

Imagine the load on the hardware if it had to produce an object 11 times per second, times 2, and the machine guns with an even higher rate of fire... It's gonna take a while until the hardware for that will be available. As stated before, the lack of quantity is probably compensated for by the amount of damage.
So to answer your question: yes, there are less bullets than there should be, and no it's not possible to fix this.

Disclaimer: I'm no developer, and only have amateuristic knowledge of developing, so I hereby apologize in advance for any untrue statements