All things being equal
Well in reloading, I cant name one damn thing that is equal. You can cut down on the variables but never elininate all of them.
Ever weight the bullets right out of the box (+- as much as a grain in some cases)
Powder ( different lots, was it measured by weight or volume)
Brass some cases are thicker other are lighter (Even in the same lot)
Barrel of the rifle (Hotter, colder more worn or brand new from the test)
The test equipment (new or old , digital or analog)
When I start a new load I usually try to cross reference from as many sources as possible to find my "safe" starting load and work up from there.