I only knock my pals out the way (and vice versa) for the shits and gigs. I’m far more courteous with strangers. If they’re there first, they can have it.
No etiquette just first come first barge gets it. I usually don’t fight for the power and rather cover my random teammates whilst they get it. As long as they kill the enemy I don’t care who has the power ammo. I want my IB tokens!!!!
If you are having this issue frequently you may consider joining a clan and playing with people you can talk to on discord and plan out who is taking what...
If you are good with your heavy weapon like with my sword i generally get 8-9 kills with it i find people leave it. Then my guild just knows. Let swordgod have his bloody sword