First, I am not an AA grade but I have looked at all sorts of factors for the heck of it. I did try weighing tins and came to a possible conclusion that the heavier ones were longer than the lighter ones. I.e. the wire stock gets chopped up before injecting in to the mould thing and there is a small variation in length. I never really found a difference in grouping - maybe the slightly longer skirt helps the flight of the slightly heavier pellet?
I gave up and now just shoot 20 pellets out of a new tin, if they group around where I aimed they are good, if not I don't waste any more time with them (sometimes sizing can make them group though). Not even convinced tins from the same sleeve are always the same :-)
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