If I were to encounter a 20 grain weight variability from the same lot of arrows I would begin to be a bit concerned. Not because of the weight difference itself but because itmay bean indication of sloppy control in the manufacturing process that could mean a significant variablity in spine, both axially and from arrow to arrow. To say it a different way, if the ONLY difference was weight I'd be O.K. with it but I think that that much weight variabililty could also indicate other more significant problems. Remember, manufactures often "sort" the results of a production run by straigtness and sell arrows at a premium price that conform to a tight straightness specs some times not even mentioning tolerance for spine and/or weight.