Excessive Force Pre-Requirement from
FIASCOcomedy: Cant access crucible til level 4. You also cant access Heavy Weapons until you have access to one in game, (After the 4th mission you get one from the Gunsmith in the Tower). . .
This is actually extremely easy, when playing PVP you will start with no heavy ammo, but listen to the announcer and he will announce when heavy weapon ammo drops.
Look for a purple ammo icon and run to grab it, be quick because you are fighting to get it. Once you pick up heavy weapon ammo, hold the Y button to swap to your heavy weapon.
Enemy steal your ammo? Kill then and grab it for yourself, it will be a purple cube on the ground.
All 25 kills do not have to be in 1 match, it is cumulative.
Good luck and have fun! I really enjoyed using my heavy weapon!