I would like to personally thank Johan Loubser of Western Powders for supplying the test data for my handloads. He has been very helpful and gone beyond the call in providing technical information in my quest to achieve what I consider the ultimate Indiana deer rifle. Consider Accurate Powder on your future loading projects. Hopefully, some of you will benefit from the data provided. The Indiana firearms season is just around the corner and I am really looking forward to it. I wish you all the best of luck this year and most of all, be safe.
One important thing I learned through this testing is that the .357 Maximum pressures are really affected by cartridge overall length. I’ve only included data that did not exceed the maximum SAAMI spec of 40,000 psi. I also did not include any test loads with extreme compression, greater than 120% load density (LD). While 1680 compresses well, when you get beyond 120% LD, this type of load becomes impractical. My Ruger No. 1 has a very long throat which allows considerable longer bullet seating. This goes a long way to keep pressures down. My first .357 Max. rifle, a T/C Encore with an MGM barrel had a much shorter throat, as I requested when I ordered. That rifle shoots very well, however, what I have learned since then, if I am ordering a custom barrel, or having a .357 Mag reamed out, I would request a longer throat that would allow a longer C.O.L. to allow heavier powder charges and higher velocity while maintaining lower pressures. It looks like you will gain approximately 20 fps from the 10” test barrel for each additional inch of barrel length. Where you reach the point of diminishing returns is unknown to me. If I had to make a best guess, I think you will see maximum velocity around 20-24” of barrel length. If anyone has data to confirm this, I would be very interested in hearing from you.
