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Old January 27, 2021, 10:09 AM   #2
Unclenick
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Join Date: March 4, 2005
Location: Ohio
Posts: 18,685
CAUTION: The following post (or a page linked to) includes or discusses loading data not covered by currently published sources of tested data for this cartridge (QuickLOAD or Gordon's Reloading Tool data is not professionally tested). USE AT YOUR OWN RISK. Neither the writer, The Firing Line, nor the staff of TFL assumes any liability for any damage or injury resulting from the use of this information.

I've used both QuickLOAD (for about twenty years) and more recently GRT and found they are sometimes about spot on and other times can miss by several percent. In a fairly technical discussion on another forum, an interesting case is made for the limit of velocity prediction accuracy being in the 1%-2% range by the Mayer-Hart system, which is an analytical solution. The point was made that attempts to allow for more precise adjustments of factors than that older system allows for have actually made predictions of velocity less precise. I've seen them miss by over 5% in the two software packages mentioned, which provide iterative numerical solutions. It turns out the cumulative error possible with all the available variables can be less accurate than some general rules of behavior. GRT is soliciting user input of Pressure Trace data to adjust its models and powder data to close in on more accurate solutions, and only time will tell how close it can get.

Here is a paper about the Mayer-Hart system with derrivations and here is a Mayer-Hart calculator. You still need some technical information about the powder to use it. Vihtavuori publishes their data, which is why their powders' values are listed for use with the calculator. You can extract some of that information from QuickLOAD's vivacity data and from GRT's powder data for other powders, but there is some effort involved.

Anyway, the bottom line is probably that if you take a QuickLOAD or GRT maximum load and knock it down 10%, it should be good enough to try, but before I did that, I would run the powder model against some published loads using it first to see if you can spot a trend for pressure or velocity to be low or high and adjust your expectations of accuracy accordingly.
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