Just for clarity here are the actual rules:
Weapon mounts: Vehicles may be equipped with a
number of weapon mounts equal to their unaugmented
Body ÷ 3 (round down). Standard weapon mounts may
hold any assault rifle or smaller-sized weapon and 250
rounds of ammo. Heavy weapon mounts count as two
weapon mounts and can hold any weapon and up to 500 rounds of belted ammo or up to Body rockets/missiles.
All weapon mounts are operated remotely and can
target a ninety-degree arc of fire (horizontal and vertical).
Manual operation can be added, but only for vehicles,
not drones, and at extra cost.
Note: this does not say anything regarding modification of weapons, altering of fire modes, changing of clip/cylinder/break action/muzzle loader/internal magazine.
It just doesn't.
The rules are vague and leave things open to interpretation either way and are further muddied by the requirement for belted ammo on the heavy mount.
Does that requirement therefore preclude non-belt fed weapons? so a small mount can make a pistol into a 250 round capacity, but a large mount can't do the same for a sniper rifle?
If so, why? If not, why not?
The rules are vague and for those that use previous precedents from earlier rules, i'm reasonably sure that small mounts in sr4a require belt-capable weapons to utilise the ammo bins, hence everything had 100 round drum mods and dual magazine feed mods to give 200 round capacity for non-belt weapons.
Note i am not stating an opinion here, just presenting facts.
CBA with yet another argument on this topic