Sentry HMG reload question

There is a topic on mortars, but I cant figure out how to reload my sentry machinegun ?
I have a ammo truck and tried all kind of piruettes withboth the gun and truck...   

I finally found the way how to reload sentry MGs.

You have to get a UAV units controller and log in with that to your MG.
Then if you are near ammo truck you get option to resuply it.

It cost a lot to do that *14500  but who cares when need is big.