You can get additional ammo from ammo crates in the map.
Hochfir from ammo packs/station 165 max; from ammo crate 220
Crotzni from ammo packs/station 120 max; from ammo crate 160
Didnt test it with other guns.
http://fs5.directupload.net/images/160818/temp/rrfnstxf.jpg
No Spares Augment