Page 189 of the sixth printing of Tactical Operations: Advanced Units & Equipment introduces the ability to allocate ammunition on a per-shot basis, rather than per-ton (or half-ton in the case of MG ammo). A major benefit of this is the ability to mix ammo varieties (such as standard and Fragmentation SRMs) without allocating full tons for each type.
Adding additional ammo varieties requires additional slots, as they can't share a single slot. Does this mean that merely changing the ammo load could require a Class C refit due to using more slots (page 211, Campaign Operations, fourth printing), even though the total weight of ammo hasn't changed?
My inclination is to say it does not require a refit, so long as the total tonnage in a location allocated to a given ammo type does not change. That allows players to adjust ammo mixes freely, so long as the design has enough unused slots in the location to accomodate more types.
For instance, a Wasp 1A could choose to load 25 standard SRM 2 shots and 25 Inferno SRM 2 shots without a refit, as it has enough slots in the left torso for both. However, removing 25 shots from the bin would require a Class A refit to free up the mass for use elsewhere: without a refit, that would count as a half-loaded 1-ton bin taking up the full ton.
By the same token, loading 25 standard shots and 25 Acid shots would be a Class C refit, as 0.5 tons of SRM ammo have been added to the location. Loading 25 standard and 12 Acid, meanwhile, would only require a Class A refit if counted as 0.98 tons rather than 1 ton.
Note that this is basically the same approach used to track ammo on Small/Large Craft (page 194, TechManual, sixth printing), but with locations rather than weapon bays.
