[Unclenick]

Drawings in loading manuals are usually the SAMMI maximum for any cartridge. These numbers will be plus zero minus something. Probably two or three thousandths. The SAMMI .308 chamber is about 0.011" wider than the case and is minus zero plus a couple of thousandths if I recall correctly? I cant find where I put the copy of the SAMMI drawing for .308 that I have.

The bigger question is, why do you care? The SAMMI spec should only matter to you if you are loading ammunition for sale and have no idea what gun it will shoot it? The only purpose of the numbers is to guarantee compatibility with unknown guns. When the round fires in your own gun's chamber, it expands to fill that chamber, becoming "fireformed". This new volume is the one that determines load pressure in your particular gun with the powder charge and bullet in the case. When you resisize, if you are loading singly, just size the neck for best accuracy and leave the rest of the case custom fit to your chamber. If you need the ammunition to load from a magazine, then you need to full-length resisize, but usually only enough to push the shoulder back about .002" or so from its fireformed position. This is especially useful to know if you fire the .308 in a gun with a 7.62x51 NATO chamber, which is about 0.004" longer at the headspace. No point in working the brass all the way back to SAMMI for that bigger chamber. Some self-loaders are more picky about getting the case to feed, and may require you to use a small base sizing die to narrow the case more than a standard sizing die does, especially if you are not pushing the shoulder back to original position.