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https://www.milsurps.com/attachment.php?attachmentid=111141&cid=1&stc=1

Although it's true that a standard FL sizer may reduce body diameter when backed off a bit (less so with a strongly-tapered...

CS's photo shows a completely normal fired case - unlikely from an "improved" chamber.

https://www.milsurps.com/attachment.php?attachmentid=111132&cid=1&stc=1

Since a new .303 case "headspaces"...