Maybe I can say it a little nicer than stick. Every lot of primers, cases, and powder are a little different. Not counting the rifle chambers they are tested in. So reloading manuals give you a place to start that should be safe in your particular rifle.
There are several manufacturers of a powder in the 4350 burning range. They are all a little different. Then there is the lot to lot difference. Hasbeen
Yes and like you said, there is a difference in rifles. Many of the loading manuals are worked up with a universal receiver and who know who's barrel. Heck even if they happened to use the same rifle as the one you have is no guarantee that it will be close to your rifle.
Given all of the variables it's a wonder they can even give you a close recommendation.
