I see what you are saying, for example, for a 180 gr bullet and IMR 7828 powder for a .300 Weatherby, Nosler lists a maximum load of 84.5 grains, and Hornady lists a maximum load of 81.9 grains.

That's why for all new loads we start several grains of powder below the listed maximum, regardless of the bullet or manual, and work up our loads, constantly looking for excess pressure signs.

Even though a bullet manufacturer lists a maximum load for a bullet that they make doesn't mean it would be safe in your gun.

I have manuals from each of the bullet manufacturers of the bullets that I shoot, and when I first start working an new load I will go to that bullet's manufacturer's manual first. But sometimes a manual won't list a powder that I want to use, and another manual would for that weight bullet.

Also, many manuals list loads for bullet weights, not specific bullet styles. For example, for .300 Wby, my Hornady manual lists the same load for 7 bullet styles for 178-180 grain bullets. These include spitzer, spire point, flat base, tipped boattails, HP boattails, and round nose bullets.