Interesting you were able to pick up on that, nice eye. It doesn't make a big difference to me because aesthetically they were probably made that way as to justify the hand cannon being a secondary (the design is bigger and more intimidating). Same with the heavy machine gun, as well as a justification for the ability to reload faster. Let's investigate the M60 in CoD, extremely realistic but that thing is a beast to reload. I'll give the technicians in the destiny world that they had the technology to combat the general setup for heavy machine guns to make the reload a lot faster, thus more useful in combat, since it feeds into the top.