so you're cool with the fact that the collective human empire builds space ships that dwarf continents and contain munitions to completely eradicate all life on a planet. They then fly these through a realm of nightmare made real to cross the galaxy. Upon reaching their destination, they shoot giant space-bullets at the ground. These space bullets impact the earth and disgorge their contents - genetically enhanced super-soldiers, wearing high-tech battle armor equipped with all sorts of neat target-finders, sensors and communications devices. These warriors un-sling their armaments - veritable cannons that fire rounds so large they can punch through battle-tank armor - and then charge headlong into the enemy, where they can punch them in the face repeatedly with oversized, glowing gloves?
You're cool with that, but the fact that the assault cannon's ammunition hopper is a bit small breaks your suspension of disbelief?
=)
naw, this is the same as "how does a space marine actually fit in his armor?" or "how would a Cadian fit inside a suit of space marine armor?" or "how do 10 space marines fit inside a rhino?" or "how is a tervigon able to gestate & hatch potentially 105 gants in a mater of minutes?", etc.