don't get too hung up about your chrono accuracy, with optical type chrono's you will find the data is consistent for that session but depending on lighting conditions you may find variations from 1 session to the next, in short they are great for checking E.S (extreme spread difference between highest and lowest velocity in that session) and S.D (sectional density the spread above or below your average speed for that sesssion) but your best bet for confirming your actual velocity is drop so shoot at 100 yards then shoot at 200 or 300 and work out your velocity from the drop at those distances.
hopefully that info is helpful and I'm not bamboozling you. Took me ages to get my head around optical chrono's being consistent but not necessarily accurate
so given your above figures:
13/06/23 session: E.S of 85fps and S.D of 42.5fps avg velocity 3027fps
06/07/23 session: ES of 39fps and S.D of 19.5fps avg velocity of 2988fps
what this shows is that upon studying the data your load is not particular stable showing quite a wide spread in velocity particularly in the 13/06 session, but that doesn't mean it wont shoot fantastic groups at 100yards
It may not matter much at 200yards or 300 yards so if this is your aim don't stress it. it really starts to make a big difference at extended ranges.
Try checking your ballistics at a range of say 600 or 700 yards and see what the drop difference is at your maximum and minimum velocities.
I'm not poo pooing your shooting or your work just putting a bit of context on it. When I work up a load especially for longer ranges I'm looking for the charge weight that gives the lowest E.S and S.D as this will mean the most consistent POI at longer ranges due to being much less variation in velocity. Once I find a good stable velocity charge weight I can then tune the group size by adjusting the seating depth. this kind of load development can be a little component hungry, but sometimes you just get lucky too.
I'm happy to explain this stuff further but I worry that I am making this very complicated and if you're not intending to shoot long range it's probably to a large extent irrelevant, but if you want to know more I'm happy to lead you down a very deep dark rabbit hole limited only by the depth of your pockets and sanity
..........Micky Duck will no doubt be along shortly to voice is dislike of chrono's and my load development complexity
but it does have it's place depending on your intended goal.
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