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I also was a tad suprised to see my velocities were lower than the reloading manuals stated. 47.0 should yeild 2700 fps according to Sierra but netted me 2560 fps.
-Is it my chronograph?
-Is it my lot of powder?
-Is it my like new HRA barrel?
It could be chronograph misalignment, I doubt it is the powder, and it could be the barrel.
Being off by 50 fps is an insignificant difference. I think with a Normal Distribution 63% of the time the true lot average will be within two standard deviations of the average. Or something like that: find a college kid who accurately remembers his statistics for the correct explaination.
I try to shoot a "reference" load over my chronograph. If velocities are way off, I readjust the chronograph. Instrumentation error is real.
Also, shoot some ball ammo over the chronograph. If it is slower in your barrel than in the books, guess what, its your barrel.
When the Government accepted powder, the Government inspector carried a reference cartridge. The load was calibrated in the Government pressure barrel. He fired the thing in the contractor barrel and measured pressure and velocity. Which of course were different from the Government barrel. He then adjusted the data by the differences.
There are things as fast barrels and slow barrels. If you shoot a "calibrated" cartridge in a barrel and get low velocities, it is my belief that while velocities are less, pressures are not. I also believe that high velocities in a fast barrel means high pressures.
It is lose/lose no matter what you do.
https://www.milsurps.com/images/impo...DSCN9365-1.jpg