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From what I have read about it, in the earlier years, Speer worked up data for some guns without really doing pressure measurements and just left it up to the Ballistician to make a judgement call on the load's quality, safety, etc.(Three load ranges) Other's were not re-evaluated for many years.
Now Speer is changing over to Piezo-electric pressure testing and is phasing out the copper-crusher methods gradually. This has lead to the later editions with some toned down loads. The 357 Mag is one noteworthy one.
I try to match the approximate time I purchased my smokeless powder to the approximate edition of the reloading manual publication dates.
This is a reasonably half assed way of matching a powder lot year to the load data time frame.
Follow normal safety considerations also.
Have Fun
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