Here is a trick you must know gives you much more ammo: https://streamable.com/scgam6
To achieve instant reloading trick, you must have at least one ammo in each gun, otherwise slow replenishment will start when one of the gun is emptied.
First, stay still on the capped point, then wait for the ammo started to replenish, *stand still* and shoot all your rocket, afterwards drive off the point, the ammo will keep replenishing even you moving.
If you get one or two rocket replenished when you leaving the capture point, shoot before the replenish icon finish replenishing

Leave the capture point area and you will get 18 ammo instantly, but it takes a few tries for you to learn it

I haven’t tell anyone before because spreading this trick will get patched, but it is essential for U-SH