not "armory", but "ammo"
well its truly strange when rocket launcher with 9 holes somehow eats 5 rockets. Still, basic consumption of 5 is legacy from Batte Mechs, where 5 was only possible. Now it is expanded to 5*x where x is whatever you want.
But of course back then players didn't have continuos energy drainers, overheaters, swords etc., so it would make sense to actually use other values of consumption with some weapons. Like 12 or 16