Here's a thought... Change the nature of special ammo completely. Obtaining non primary ammo is a subgame that can net advantage for your team. Opening both heavies or popping a super on the opposition at heavy spawn is big game. You also net an advantage by popping more special crates than the opponent. What if special was just removed from this subgame? What if every one to two minutes in PvP you simply get some number of special added to your reserve? Won't happen, but that could be a fun and balanced way to restrict secondaries being used as primaries but would still allow for diversity in the secondary slot. It could also force primary usage because of hard limits on secondary ammo each match...