[2019] MCC pistols and voice chat?

I noticed sometimes you can charge the plasma pistols and sometimes it doesn’t let you. Is this dependent on the specific Halo game and/or game type? You used to be able to charge the boltshot in 4 but now you can’t? Also, with online multiplayer, a lot of game modes don’t allow voice chat? Halo 2 and 4 online doesn’t allow me to speak.