Thread: Load Data Conundrums.

Greetings All,
While I was trawling through some of the Hodgdons load data for the 7mm Remington Magnum the other day I spotted some odd data. The loads for the 150 grain Barnes TTSX BT were considerably higher than those for the 150 grain Nosler Partition. Due to the extra length and hardness of the Barnes you would expect it to be the other way around. A conundrum if you like. The 7mm Rem Mag came out in the 1960's, loaded with a powder not available to handloaders so there were some pretty spicy loads listed when people were trying to match the claimed factory loads in the days when few handloading manuals. But this data was recent and had pressure data with it, a conundrum if you like. Being the OCD type of chap that I am I just had to make sense of it.
First the data for the Hodgdon/ ADI powders and the Nosler projectile was old with pressure in CUP (Copper Units of Pressure). At the time that pressure started to be measured in PSI it was found that the old copper crusher system was understating the pressure. Further it was not picking up variations in pressure in some cartridges, the 7mm Rem Mag being one. Loads were reduced for some cartridges around 1990 so the load data for these powders could be on the light side.
Next I compared the Barnes and Hodgdon data for the Barnes 150 grain TTSX BT. The Barnes max loads were roughly the same as the Hodgdon start loads for the 4 powders powders in common. Further Hodgdons got around 100 fps less velocity than Barnes with the same load. So the Hodgdons barrel was slower.
So there we have it. A combination of old soft data and higher pressure data in a slow barrel. One thing that did not change as much was velocity. Hodgdons only got from 80 to 120 fps more velocity for all that powder so working up to a velocity rather than a charge weight has a lot of merit, something I have been doing for some time. Velocity is a better measure of pressure than anything else available to the handloader.
Regards Grandpamac.