I explained this in the
More Weapons thread. That link contains the basic explanation and images, but I'll sum it up some things here.
For each weapon in the game players would be able to customize magazines with parallel feed mechanisms allowing multiple ammo types to be switched on the fly. Guns with multiple fire modes could restrict the types of ammo that could be fired. Ammo types would modify the accuracy, cone of fire bloom of a gun and even reload times of a magazine.
Along with this idea is the splitting of anti personal rounds into anti-health and anti-armor rounds. Anti-armor rounds would take down armor easily but do less damage to health whereas anti-heath rounds would do more damage to health and less to armor. The original Planetside armor piercing rounds would turn into anti-heavy armor rounds which would do more damage to things like maxes and vehicles.
I think it might be easier to just show you quick prototype I threw together:
Demo
I think that demo sums up the idea pretty well. I'm tired of coding it anyway so I won't be making any changes to it.
Essentially this idea would complicate the weapon system immensely and open up a lot of options for more skilled players.