Even the PT may need 'calibration' on a particular rifle. Probably will, IME. Calibrate it like Harold Vaughn suggests in his book Rifle Accuracy Facts if you can (using a hydraulic system). If you can't do that, use factory ammo as a reference point, depending upon how well your rifle & speeds match with factory test numbers. For example, my Creedmoor rifles both shoot/shot Hornady factory ammo very close to advertised speed, and they have/had 24" bbls just like the test barrel. That plus specific pressure data for that lot of ammo allowed me to get a good reference for the PT on that rifle.
Where do you source original pressure information for factory loads?
