It's about Pressure and burning rate mostly.
OAL tells you bullet depth in the case, and thus case volume. Case volume is the second biggest contributor to a powders shifting burning rate. It also gives a standard reference point against your rifle, to have an idea of how much gas bleed-off and resulting lowered Pressure you will have. To a point (back to case fill) the deeper you seat the bullet, the lower the Pressure because of gas bleed-off.
Without double checking reamer prints, I'm of the opinion that Savage tends to throat their military cartridges with a more NATO throat. Keeps a larger margin of safety for those who love to keep stuffing more powder in cases. Far too many shooters think that unknown/uncalibrated cases and primer cups somehow magically are an accurate reporter of SAAMI pressures. They cannot. So why not toss in a safety step.
I am like you in that Book OAL is never considered, I measure every bullet in every rifle of mine. As long as you don't think you can match/beat book velocities, REGARDLESS of charge weight; you are OK Pressure wise. Just watch velocities as you work-up. Book data is fired in SAAMI minimum spec test equipment, mass produced rifles aren't that tight. So unless you had a barrel built with very specific and tight specs, there are almost never any "fast" barrels, just higher pressures.
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