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Old January 25, 2012, 10:58 AM   #2
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Join Date: November 8, 2007
Posts: 2,001
If it were me, I would measure the water capacity of my new .357 magnum brass, then do the math to figure out how much of that water capacity remains with (1) the bullet seated to the depth of whatever load data I have, and (2) the bullet seated to the depth I need to fit the cylinder. Subtracting those two capacity losses from the empty case volume gives (1)the powder space in load data, and (2) the powder space in the cartridges you inend to load. Adjusting the charge weight in the load data by the ratio of the powder spaces should give you a safe way to figure a max load for your COL.

But, remember that changing case brands, primer strength, etc. can make a substantial difference.

So, for example, if the data you have is shot in Winchester brass and you have Federal brass, you should probably get some Winchester brass to measure the internal water capacity, rather than just assume that it is the same as your Federal brass.

As for primers, most H-110 data should be for magnum primers. But, if you try the same technique with another powder, such as AA#9, be aware that Accurate has switched from shooting their data for the .357 with standard primers to shooting it with magnum primers (to protect the dopes who just ignore the data and use magnum primers for everything in the .357 because it is a "magnum"). Switching primer strengths can make as much or more difference than slighly changing COL, maybe as much as 11,000 psi.

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