Monday, December 27, 2010

Additional Comments on Alloy & Pressure Matching for Accuracy, the Myth

Details and background can be found in this prior post

I noticed some interesting data from my test records: All data is from testing with my 357 magnum, a Taurus 66, 6inch:

With a 358-429 168 Keith bullet: the most accurate loads & alloy:

700X at 28-30,000 PSI wiht BHN 7-8
HP38 at 18-20,000 PSI with BHN 7-8

These two loads are capable of groups less than 1 inch at 25 yards, from a rest.  The reason I favor 700X is the consistency of the tight groups.  It's just a bit better.

With the same cast boolit, the most accurate load with the 2 different powders is with different pressure levels.  It turns out the most accurate alloy was the same for both pressures.  That makes the comparison very relevant to disproving alloy and pressure matching for accuracy.

The most accurate load for a 158 SWC is:

HP-38 at 24-25,000 PSI with BHN 7-8

This is another pressure level for the same alloy and is the most accurate load I've found for a Lee 158 SWC TL cast boolit.

Looks to me that the most accurate loads depend on "boolit design & weight" matched to the powder.  The pressure ranges from 18,000PSI to 30,000PSI for the same alloy.  This pressure range is not even close to the 10,370PSI the formula from Lee provides.

When pursuing the best accuracy, the calculations don't work in a 357 revolver.  Different pressure levels have proven to be the most accurate with the same alloy, when using the most accurate powders.  Maybe I'll have to refine that claim, however magnum/slower powders just don't beat or even equal 700X and HP-38 for accuracy.

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