The loading manuals are made by people who print the results they got in their rifles, etc. Some use sporting rifles, some use universal receivers but they all have different rigs so the "max" loads you see only reflect those differences. YOUR rig and mine are like none of their's so our MAX may or may not be the same as theirs, this is not chemistry class in which we do "exactly this to get exactly that" results.
I know one guy who got badly blown primer pockets in a still new Win 70/22-250 with Hodgdon book midrange charges of Varget. If he had started at a presumed dummied down max load he would have surely had a bad occurance. Meaning, anyone thinking the book makers fudge the results so we will be safe is wrong! Do what the books say, "start low and only work up if no pressure signs occur" or you may get a viscious surprise.