What's this drop?

[Snow]

Keeps dropping off grineer, shimmers like a usable and has this yellow beam but can't seem to use or pick them up?

https://i.imgur.com/HLsS0Xq.jpg

[croquemorttime]

Hi,

it is heavy ammo : used to reset the timer for summoned Archguns... (droped by heavy units usually)

[Snow]

Ah ok, thanks!

[ShatteredPumpkin]

refills ammo for archguns and resets its timer after running out of ammo for it