Re: Weighing vs metering powder
This sounds like a terminology issue, as I'm not aware of any commercial maker that actually weighs their charges priot to dropping them. I don't know whether Federal is plate loading or using an in-line system, but the charges are almost certainly dropped via a measure, or "meter" which is (I suspect) where the confusion here comes from.
Richard has explained this, and I'll go with his explanation completely. I have seen Lake City weigh their ammo, and they still do this as a regular part of their inspection process. The purpose there, however, isn't to ensure the precision of a charge weight, but to guarantee that each round has enough powder inside to postively assure that it can't stick a round in the bore. Very bad form in combat ammo, and makes for very unhappy troops!