Originally Posted by apexmtnman
"I've had Winchester brand .338 Win. Mag. brass with belts headspacing at .218". SAAMI spec's state headspace is .212" to .220", but if sized cases headspace off their shoulders, then belt headspace doesn't matter. Especially if you somehow size the body diameters immediately in front of the belt back to virtual new case dimensions."
Bart B, it's amazing to me how many people don't understand this (setting fired bottleneck case shoulders back a bit), resize your belted cases exactly the same as you do non belted cases by bumping the shoulder back a couple thousandths and the belt is a non issue.
Best thing about doing this is those belted (and rimless ones, too) will center perfectly up front in the chamber regardless of how much clearance there is around the case body behind the shoulder and around the case neck.
It's best understood without pictures by noting how rimless bottleneck head space gauges fit the chamber. When the bolt closes on them, the shoulder on the guage matches the shoulder in the chamber fits and centers perfectly in the chamber at the shoulder when the bolt's closed and headspace is a bit short stopping the bolt from closing all the way. The center of that gauge up front doesn't have a neck, but if it did, the neck would also be perfectly centered.
If one can imagine a .243 Win., .260 Rem., 7mm-08 and a .308 Win. case all being chambered in the same .308 Win. rifle. When the spring loaded ejector in the bolt face pushes them forward until their shoulders stop against the chamber shoulder, the necks on each one is perfectly centered in the chamber neck. Lots of room around the .243 and less as neck diameters get larger. When the firing pin strikes the primer, each case will be driven harder into the chamber shoulder; if the in-line ejector doesn't center the case shoulder in the chamber shoulder, the firing pin smacking the primer will. The primer detonates after the case shoulder's hard against the chamber shoulder. So a .243 Win. live round's bullet will start out dead centered, straight down the bore in a .308 Win. chambered barrel.