A .5 gr. spread usually indicates very long grain powder, a really crappy measure, inaccurate scale, poor powder measure technique. Maybe even the involvement of a ceiling fan.
Seriously, a combination of a few of the above reasons is usually needed to have an error of .5 gr. If ya can't do a little improvement on these factors you're just gonna have to throw light charges, and trickle them up to spec.
What kind of powder, and how large of charges are we talking? jd