2" different lead on frame to frame, side to side, is a lot of lead to explain factory differences in swing wt. I think some are set up head heavier for a reason, not that they all are matched to swing wt.
fed lead tape. That's a lot of weight, 4" of lead on each side, 8" total, is about 7grams heavier, and Fed's frames are ranged from 357g-364g on purpose. It's not to balance out the specs, it's to give more plow through on some frames for serving/vs. returning. He switches them up.