Bear in mind that the 45 ACP (in a semi auto) headspaces on the case mouth. Too short and the round may misfire, too long and it won't allow the slide to fully go into battery. You need to determine what your gun "likes". The measurement from the manual is usually correct and thats what I use 99.9% of the time.
If the rounds are going into a revolver using clips then you have more leeway since the headspace is now transferred to the rim.