The 7.65 has a pretty good taper from base to shoulder, the Luger is designed to handle a tapered case. So Georg didn't care. Other brands have had to work with what was there.
I thought the truncated cone did ok in pistols (It does in mine but I do not have a Luger at present.) and the roundnose came in with the trommelmagazin and big sticks for early SMGs.
Any road, I don't know if the 7.65 would open out to a straight case with 9.5mm bullet.
Surely a 9.3 would fit and the diameter was already well known in German barrelmaking circles.
Would we now have a .40 cal if there had been a .366 well established on the market?
The only other tapered 9mms I recall are the 9mm Bergman Bayard/Largo and the 9mm Mauser Export. They have about the same head and mouth diameters as the Para, but the taper is less because the cases are longer.
The .38 Auto and 9mm Browning Long are straight, albeit semirimmed, the .380 and 9mm Steyr are straight rimless.
I would expect a replacement sideplate to reduce the resale value a bit. The legend is that throwing away the sideplate was a quick way to disable the gun before capture and not give the dirty American a working souvenir.
