make HMG riflemen have to reload when they 'change class' at a spawn point, especially because of flag maps. I lie down on flags and continuously shoot forever, and I rape people on district, escort and urban chaos.
so your gun magically refilling his loader without loading while changing to the same class does not seem silly?
It's only really a problem for weapons with long reloads, but weapons with short reloads would presumably not suffer from it being a general feature much. Although it is a bit annoying to have to reload everything. What about if changing class just doesn't affect your current ammo? If you get a new gun you have to fill it from the ammo box, if you don't you don't. Make ammoboxes also fill all your guns when used rather than just the current one and you shouldn't have much annoyance, combined with solving the problem of exploitability. If you change skill, no problem, if you change a weapon or class, stop at the ammo box for a few seconds to get ammo for your new guns. Ammoboxes are only really for supply lines, if there's an ammo box there the game should assume you can refill your ammo from it and do it as quickly as possible. If you had my idea of armories allowing full-ammo spawns, perhaps make it so changing class when an armory is nearby half-fills your ammo unless you already have more of it for a given weapon.
changing class absolutely needs to give some ammo back, though. if you find yourself defending a rax with no nearby armory you shouldn't be forced to suicide or die to get more ammo.