Could be length of barrel affect or maybe not. Those COMPLETE RELOADING MANUALS for one caliber are great because they pull data from a number of other manuals for that caliber. However, I suspect those one caliber manuals may have some obsolete data from one or several other component companies. Various component companies update thier data a various times, and those one caliber plastic spiral bound manuals may have missed that newer stuff. I know that's the case for the IMR Powder section of my .270 Win manual.