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Also, has any research been done as to what a 1 grain of charge difference would mean at 100 and 200yds?
Info on differences in velocities, pressures and groupings would be helpful.
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Richard Lee discusses this a bit in his reloading manual. IIRC, he found that
within the small range of min-max loads for a given powder the pressure and velocities increase linearly with powder charge. So if a manual gives the velocities at the minimum load charge and the maximum, then you can find the in-between changes as well. Say a certain table entry shows a range of 5 grains, from 40 gr - 45 gr, and the velocities are 2,500 fps - 3,000 fps (difference of 500 fps). Therefore, a 1 gr increase from 40 gr to 41 gr should result in a velocity increase of 100 fps to 2,600 fps. [ETA:
WARNING: This is only an EXAMPLE of the relationship. DO NOT increase 1 gr to get 100 fps!!!!
In actuality, the pressure and velocity increase are some sort of curves as volume and friction and other factors change at different load and velocity levels. But within a relatively narrow powder charge range you can
approximate the other changes as a linear relationship. I believe he mentions that some powders have a flatter curve and used H4895 as an example of a powder with a very long linear change.