I posted this on marlinowners.com and am posting it here as well for the same reasons:
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Over the last couple of years I have shared my reloading spreadsheets with many folks on the old Marlin Talk board and some of you folks here. (For those that don't already know, the spreadsheets include over 250 load recipes for the .45-70 from various powder and bullet manufacturers, plus load, chrono and accuracy data for the 17 .45-70 loads I've worked up.) Although I send the spreadsheets out with a word of caution to verify the load data against the original source, which is referenced with each of my loads, I thought I would share some pressure information I just received on the North Fork loads.
Some months ago I sent 5 of my loads to Mike at North Fork for pressure testing. Yesterday I got the results back. Pressure-wise, my North Fork loads run 23% HIGHER than PMC's 350g loads but 4% LESS than the Buffalo Bore 350g JFN loads Mike tested. This definitely puts them at the high end of acceptable pressure in my book. Still, I believe they are safe in my rifle and I will continue to use them unchanged. That said, to anyone using my data:
PLEASE USE CAUTION WHEN WORKING UP TO MY LOAD DATA!!!!
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The starting point for my load development for the North Fork 350g bullet was Hodgdon's data for the Hornady 350g RN. Because the North Fork has a solid copper alloy shank, it is considerably longer than the Hornady or bullet and sits deeper in the case when seated to 2.540". Because powder space is more limited, I expected higher pressures for a given amount of powder, which Mikes testing confirmed. My final load was 3.0g less H4198 than Hodgdon specified for the Hornady bullet, as follows:
Starline brass @ 2.095"
CCI 200 primer
North Fork 350g @ COL 2.560"
51.0g H4198
2181fps
100 yard group (using new batch of powder, 51.5g H4198 @ 2183fps):
3 of 5 in 0.30".
4 of 5 in 1.15".
5 of 5 in 2.40" (oops!)
(I found dropping down to 49.5g H4198 and 2116fps was an even more accurate load in my rifle, based on 4 shots instead of 5, although S.D and E.S. were a bit higher at 12.5 and 30 respectively.)
Mike shot 5 loads of each type using an Oehler 43. Amongst other things, he calculated Standard Deviation and Extreme Spread for both velocity and pressure. Using my loads as the baseline, here are the results (S.D. = Standard Deviation; E.S. = Extreme Spread):
-----Velocity----- -----Pressure-------
Load FPS S.D. E.S. PSI S.D. E.S.
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PMC 1981 44 102 0.81x 3.7x 4.3x
My North Fork 2172 6 15 1.00x 1.0x 1.0x
Buffalo Bore 2181 15 42 1.04x 1.6x 1.9x
So, once again: USE CAUTION WHEN WORKING UP TO MY LOADS -- this data is provided for informational purposes only and I specifically DO NOT recommend using this data in any other rifle than mine.
That said, if you plan to work up to my loads and if you believe BB loads are safe, then there is reason to believe mine are as well, as they generate 4% less pressure with less deviation. For those of you like dla that think anything over 28,000CUP is an overload, you definitely don't want to try my loads (or Buffalo Bore's, or even PMC's, either).
