.308 Chambering.

[nwo]

What determines how far a cartridge goes into a chamber (say an AR)? Does the case chamber on the neck and shoulder, or on the taper of the case body?

Meaning, what part of the case determines where, and how it seats into the chamber. What makes it "Stop" at the proper spot?

Read More

 

[Bon Sauvage]

Headspace depends on the cartridge type. Rimmed cartridges headspace on the forward part of the rim.

Bottleneck cartridges headspace on the shoulder.

Rimless straight cases headspace on the mouth of the case.

 

[sneakboxer]

The 308 (rimless) headspaces on it's shoulder. Somewhere in the middle of the shoulder I think. Check out .308 Winchester Cartridge Guide for the particular numbers.
I hope this helped,

 

[bmgm37]

As said before, .308 headspaces on the shoulder. If it is not sized to the proper dimensions your bolt will either not lock up or will start to lock up and be hard to open the action. Not to be a broken record, but get a case gauge for every cartridge you load.....cheap insurance to make sure you are good to go before you load a bunch of rounds

308 case Gage

 

[deadshot2]

Something else to consider is that not all chambers are the same size. For bolt action rifles it is very common for reloaders to size only the neck of cases that they have fired in their rifle. The brass takes on the length and shape of the rifles chamber when fired and neck sizing is only necessary to grip the new bullet. This keeps the brass from being "over worked" and becoming brittle. It also helps to make sure that the bullet is held in the center of the chamber/bore when fires so accuracy is improved. Sizing to fit a gauge is OK but once you have a set of "fire formed" brass for your rifle, you can often reload it with only neck sizing until it gets difficult to close the bolt. Then run it through the Full Length sizing die and start the process over again. It's amazing how long brass, that is neck sized only, can last. For many competitors I have talked to commercial brass like Winchester is good for 20 or so reloadings and Lapua up to 40 times.