Pressure X Burn Rate= Velocity
If you are working up a book load and are 200 fps below book Velocity you can safely add more powder to get to book Velocity.
Yes different powder lots may have a slightly different Burn Rate however the difference effects Velocity far more than pressure. If one stops at the given Velocity for a book load given any lot of powder your pressures will be very close to book pressures.
Shod
No, No, No!!!
You cannot simply keep adding powder to get book pressure and be guaranteed safe!!!
There are a host of reasons your rifle is slower than the one used to work up the loads in a manual, but to blindly keep adding powder is just asking for trouble. Just because your velocities are lower does not mean your gun is operating at less pressure than the test gun!!!
If you a calibrated means to measure the peak pressure in your gun, then you may find that your gun operates at less pressure than the test gun and you many find that your gun can take a few grains more powder. But there are no absolutes.
