As others have said, reference several sources and you'll see different data! Back in the 80's, I developed a load development chart to be filled in later by referencing various manuals. Here is a "workup" for my Remington 700 VS .308 from the fall of '94. I was looking for a load for 168 gr. bullets and had two powders on hand that were in six different manuals on my shelf. Not only are the numbers written down for starting and maximum loads, but I plotted them out graphically for a visual.
Notice that the Hornady manual has a maximum charge of IMR-4895 that is 39.5 grains and both the Speer and Hodgdon manuals have 40 grains as a starting load! Well, they are using different test rifles, lots of powder and bullets. Primer differences, atmospheric conditions differ, barrel dimension tolerances, brass volume, etc.
What this demonstrates is that you should reference several sources when working up a load. Also, imagine what would have happened if somebody only had the Speer book and didn't heed the advice to start with the starting load. For example, "they show 40 to 44 grains, so I'll start in the middle at 42 grains". That load of 42 grains is maximum in Sierra and Hodgdon and over max. in Hornady. Not a good thing.
