Cartridges are too short

[Puretexan]

Ok I have read a bunch , and the length of a 9mm makes
a difference on weather a Luger will function properly.
If you take a 9mm Luger and change the barrel to .30
the only change you might need to make is to change the
spring. If what everybody is saying is true the really shorter .30 bullets should never work in a pistol that
was 9mm. Right? Same magazine, same everything but
the barrel.
I know I'm like a 2 year old and ask too many questions.

Paul