I found a way to shoot and activate shoulder charge. Not sure if this is well known, but with the new go fast update, this could be a great way to get fast kills in the crucible. Sprint, slide, fire, melee. For whatever reason, sliding doesn't cancel your melee charge. It couples well with "An Insurmountable Skullfort" Which regenerates health AND melee charge on kills and can be used to chain attacks on unsuspecting groups.