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Old February 2, 2008, 07:51 PM   #1
Hello123
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Load workup from fireformed or new cases?

Does it matter whether load work-up starts with once fired case or with new cases? I have new cases ready to roll and some once fired.
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Old February 2, 2008, 08:05 PM   #2
rwilson452
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you can do rough work ups with new cases but the finer tuning will need to be done with fire formed cases. In other words new cases will generally get you in the ballpark but that finely tuned load will be with fire formed. You could fine tune a load with new cases but then you would be buying a lot of new cases and hope you get the same lot every time.
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Old February 2, 2008, 10:48 PM   #3
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I think this needs a little clarification. Loads for fire-formed cases in bottleneck rifle chamberings are reloaded by neck-sizing only, and are not full length resized. They are more accurate, as a rule, but usually will not feed reliably from a magazine.

If you are talking about using a once-fired case that has been fully resized, then there is no significant difference if the new and fired cases are all the same brand and lot number. Different case brands and different lots within a brand don't necessarily have the same capacity or create the same neck tension and start pressure. A change of capacity is not usually significant between lots from a given manufacturer, but it does occur, as when Winchester lightened most of their rimless cases in the mid 90's by adopting the semi-balloon head design that had made their special Palma match cases popular for their extra powder capacity.

You can generally tell whether a new lot of cases is significantly different by trimming them to the same length as your old lot and weighing them. If the average weight of 30 randomly selected cases in the new lot is the same within half a percent as the average weight of 30 from the old lot, there is really little point in working the load up again, not even from an accuracy standpoint. A full percent difference should be acceptable from a pressure standpoint. The performance will be quite close.

There are exceptions to the above. For low level loads with wide pressure safety margins, you can use about any case, though mixing them up will reduce accuracy if the load is any good for accuracy in the first place. In the handgun world, if you are loading common standard pressure pistol loads (not +P) handgun cartridge cases are generally interchangeable. You will notice the brass used by commercial reloaders for these rounds have mixed headstamps, and that those of us with progressive loading machines usually develop safe general purpose load that let us ignore headstamps.
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