Pressure does equal velocity, with a few exceptions (secondary ignitions, etc).
There are RARELY any fast barrels...

Pick-up your powder bottle, or your manual. They have this printed warning saying "Drop loads 10% when switching lots". So, there is your swing amount.

Book data also gets shoot in SAAMI minimum spec equipment, you have a production rifle; not the Same thing.


I'm a firm believer in the theory of " If it bleeds, I can kill it".