I dont' know, but Pistols are quick to aim. This is borderline - there might be some Billy the Kid out there who simply has the reflexes. With a rifle, it's more a matter of accellerating masses and re-aligning the (inevitably lost) sights, then taking aim. The timeframe needed for this is a lot more deterministic.
Also, if i remember right, UT is unable to handle a maximum Turn speed. (This had been discussed a while back). So i assume what you are doing currently with the Minimi et al is reducing the input scaling.
I ask thee tho *g* why not simply have Mr. Infguy incur a penalty for turning to fast? Certainly the turn speed can be determined? Or would this be to CPU-hoggy. The gun could "lag behind".