My original thought was to have it lock in neutral position, since gun ammos only have an effect while loaded, thus it would swing back to neutral center during reload. It would be interesting if it would lock wherever you were aiming once it was loaded, and remain there during reload. You could create a one gunner trifecta.
What if we gave it +10,000% ammo, 50% rate of fire, -99% rotation speed, and full clip firing (like Injection). That would give it pretty similar characteristics to my original thought, with no added coding or mechanics.
Also, from that another ammo idea:
Drum Clip
+1000% ammo
-30% rate of fire.
-30 rotation speed.
-50% recoil.
Slow-firing standard rounds from an extended clip mechanism. Large clip weight slows the gun turning and helps dampen recoil.