.303 British Maximum cartridge drawing.

[Parashooter]

ANSI/SAAMI industry standards for the manufacture of firearms and ammunition.
Item #206 Z.299.4 1992
ANSI/SAAMI Centerfire Rifle
(Page 63)

"Chamber Full Size" drawing provided by E.Horton. Original source?

Unless too far forward for easy chambering, shoulder position is largely immaterial with rimmed cases in sound arms. Contrary to beliefs often stated, rimmed case unsupported at shoulder does not "blow forward" and elongate, but rather expands radially - and shortens. (Elongation occurs primarily during full-length sizing of expanded fired cases, added to any sidewall stretch resulting from end-play before firing with case and chamber clean.)