Don't Icebreaker and Invective ammo cache's reset on respawn due to death or new round/match start? If so, then the ammo regen will start over each round if players have to rely on those 2 weapons for special. Of course, the team or player(s) who manage to pick an ammo crate will have the ammo carry over if have don't have IB or Invective equipped and they don't use it all.