[Bart B.]

1stmar, every case expands to the chamber dimensions behind the neck when they're fired.

Now, about how a case fits the chamber. Especially this case to chamber fit or neck/shoulder centering and which is more advantageous. Think a bit about what I'll explain.

Take a .338 Win. Mag. chamber. It's got a diameter at its shoulder at the body part that's .491". The shoulder angle's 25 degrees. So there's part of a 50 degree V at the front of the chamber. And the chamber neck diameter's .370".

Now drop a .308 Win. case in the chamber with the muzzle pointing straight down. That case has a .454" shoulder diameter at the body. Its shoulder angle's 25 degrees; part of a 50 degree V at the front of the case. Its neck diameter's .338"

Where' the .308 case shoulder going to center from gravity pulling it down in the .338 chamber?

A .243 Win. case has the same case dimensions as the .308 case except its neck is .276" in diameter. It's also got a 50 degree V section at its front at its .454" diameter shoulder. If this case is dropped into the .338 chamber, how will it center in the chamber shoulder?

Which case will center more perfectly in the .338 chamber's shoulder?

If all cases' necks are perfectly centered on their shoulder, which one will be more perfectly centered in the .338 chamber's neck?

This is exactly the same as dropping, one at a time by itself, a marble, a ping pong ball and finally a cue ball into a funnel with its nozzle pointing straight down. Which one will more perfectly center in the funnel at its bottom?