9mm case lengths highly variable?

[villiers]

9mm Para (Luger) seals at the rim of the case and thus needs to be the correct length. If the case is too short, gas escapes which you´ll be able to see by the burn marks on the outside of the case neck. Fired cases are usually too short, but revert to the correct length (19.0mm) after sizing. So if you measure cases BEFORE sizing, they´ll normally be too short. Luger, who designed the 9 Para, realised that that there was a problem in that the cases had to have a concentric rim and be the correct length to seal adequately. He propounded a stepped chamber which some weapons manufacturers still use. The "step" leaves a distinct mark, similar to a "bottle neck" on spent cases.