Quote:
|
The numbers suggest to me one can get into trouble by relying on chronographed velocity to gauge pressures. If the relationship between pressure and velocity when adjusting charge is about 3:1 (but can be less), how can one expect charge adjustments to correct for component substitutions which can cause pressure and velocity to move in the ratio of 6:1, 10:1, or more?
|
Well yes, but what else do you have?
The slope of the pressure curve is exponential so you would expect big differences in pressures for small differences in velocity.
In all your data the higher pressure round produced the most velocity. At least I hope I did not over look something.
Back to the “what else you have”; primers lie, case expansion is pretty bogus, and velocities are just a guide, in my opinion. But they are a better guide than the physical signs of primer flattening.
Without a pressure gage, just what are you supposed to do short of blowing primers?
Primers are a big unknown for the shooting community. It is slowly being recognized that there are primers of different sensitivity but it has taken a lot of slamfire reports to get there. What we don’t know is the primer composition used, and how much those vary per lot to lot and how that effects energy and pressure. Here is a chart from a government report and they were varying composition, for what purpose, I don’t remember. Primers are not all the same and they are not all the same from lot to lot, and I believe the pressure results you see will be totally shuffled if the same brands were used, but different lots.
I have been told powder manufacturers blend their products to an industry standard of 10%. I have no idea of the tolerances on primers.
