Cartridges are too short

[DonVoigt]

I believe your premise is flawed; you over simplify what works and why.

Have you tried "standing" several 9mm and several(brands) of 7.65mm side by side- or measuring the OAL?

I've gone so far as to sort WWB rounds by length, to see if a particular luger liked "long or short" better. Yes, the rounds vary, QC just isn't what it could be.

You will find that the OAL varies significantly from brand to brand and lot to lot.
Some pistols are not very sensitive to OAL, others are- not much rhyme or reason to it.

Did you buy the Goertz and Sturgess CD? There is a whole chapter on ammo, another on magazine differences and changes(improvements".

A "generalization" , which often can get one in trouble, regarding 7.65mm/.30 luger is that pistols in that caliber are somewhat or even noticeably more sensitive to ammo. Whether it is velocity, weight, or OAL. JMHO.