Lets make a list of things which affect bullet velocity and pressure.
Some of the things which cause bullet velocity differences are.
Primers, (lot dependent)
Powder, (lot dependent)
Powder, extreme or not (temp. sensitive)
Powder measured the same, on a calibrated scale or balance.
Bore tightness and is it tapered, which direction.
Bore smoothness.
Firing pin impact strength.
Throat area of the barrel. freebore or not.
Bullet Jump to the rifling.
Moly on bullet or something else
Barrel Length.
Type of steel and condition of the bore itself.
Bullet diameters and shape.
Distance to the chronograph, actual muzzle velocity or measured at 10 ft.
You start to see why the puzzled look on someones face when they say, "I can not get the same velocity as you do, even though its the same load.
Do not forget these are high performance rounds and need to be treated with respect. Cause a .5 grain change in a Mach IV is a 2.5% change in volume. To get the same change in volume on a 7 STW you would have to add 2 grains of powder. Are we seeing the perspective here.
There have been some great words of wisdom provided in the following threads. If we need to discuss some of the variables or if I have missed some please add to the list.
Your friend, Chucker.
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