Bleeding can happen in any weapon, including firearms, melees and other projectile weapons. Bleeding is possible whenever the bullet, melee or projectile strikes the enemy. If the roll for the bleed is successful, then the health disspation will begin. Certain kinds of ammunition will cause more bleed damage than others, for example, a fragmentation grenade will cause alot of bleeding from the fragments that strike the enemy as opposed to a bullet that stays intact through the enemy.
When a player is bleeding, the player will alert nearby friendlies of his peril and start to suffer suprresion effects until the bleeding is cured. Minor bleeding will only cause minor supperssion, and major bleeding causes major supression, et cetera.