Yes indeed, load data from different published sources can seem to be all over the place. However, within one bullet profile and weight, you should see a trend that lower max charges are used with shorter OAL's. Also, take a look at the test barrel if available. Some will state what model of gun they are using, and the barrel length, some will use "universal receiver". A universal receiver with a 6" barrel will typically show higher velocity than a 4" Smith&Wesson M&P. Some books load to minimum spec Sammi chamber dimensions, some load somewhere between min and max chamber dimensions. This will have an effect on pressure and velocity in a given test platform. That is the main reason one publisher's max load may be very near another's starting load....which can be frustrating when starting out. That's also the reason its important to do a proper work up on any new load, or when changing components for an existing load. Very rarely will there be load data using the exact bullet you have, loaded to the exact OAL you're loading to, using the exact test platform the tester used. That's why its advisable to have several manuals, and between 2 or 3 or more sources, kinda read the tea leaves and get a sense of what range your work up should fall between. Good rule of thumb is to load the longest OAL that will fit your chamber and feed from the magazine. Longer OAL=lower chamber pressure. However, you can go too low and stick a bullet in the barrel. Also, you can go too low and have function problems in autoloaders, or poor accuracy. I find 115g 9mm rounds traveling less than 1050fps from my CZ75 have a tendency to impact high and to the left of my point of aim. Though, on a work up, I'd rather have that than too high of pressure and have a catastrophic failure of the gun