Rarely reloading...

As others mentioned, this movies is basically 25% to 50% shooting machine guns only..
We see them load a case per machine gun arm..etc...
Yet, they continuously fire without reloading once for almost 10-20 mins. into the battle... With all the ammo they are using. one would think that the runners would be constantly reloading the big sentry robots instead of one time only ( which is in the case of the Captain, he screams reload once and towards the end of the battle..!).
Even with 500 rounds per case, one would run out fast since they never stop shooting except to reposition themselves..!