My guess: The cartridge designers thought that the taper would make extraction more reliable. After the first incremental rearward movement, friction between the case and chamber would drop to nearly zero.

MY guess is that 9mm P is tapered so it will run through the same magazine and action as the original 7.65mm.
There was an early prototype 9mm with bottleneck case with straight body.

A straight case on that head diameter takes a 9.2mm bullet... as the Soviets found out.

Fwiw, the case for a straight-walled 9mmL.

quote:

Originally posted by jehzsa:
Fwiw, the case for a straight-walled 9mmL.

Gee, reading that piece gave me the impression that the 9mm para is the worst round ever conceived by man. Flawed since the beginning of time, nosedive after nosedive,...

I understand the theory, in practice with well-made guns, 9mm reliability isn't a real-world issue.

If the industry standard switched to a straight-wall 9mm I wouldn't care...but I'm certainly not going to have custom chambered Wildcat "9mm Auto" guns. What a PITA.

Btw, I don't remember a 9mmL jamming on me. Ever.

Either it was so horrifying that it was completely erased from my memory banks or it never happened.

ETA: Regarding the memory banks (a/k/a the cloud), age could be a factor too. No SSD there.

quote:

Originally posted by jehzsa:
Fwiw, the case for a straight-walled 9mmL.

I understand the concept, but 9mm Lugerbellums have been the most reliable pistols I've ever shot...on just about every platform I've tried. All else being equal, it's the gun that determines reliability rather than the cartridge. IMO that dude wasted a LOT of time and energy arguing against a cartridge that has never been more popular since inception. And it's only gained in popularity since his article.

Nevertheless, thank you for posting that link...it was long-winded and fruitless but interesting.

quote:

Originally posted by Jim Watson:
MY guess is that 9mm P is tapered so it will run through the same magazine and action as the original 7.65mm.
.

This would be my guess also, Jim, as the P08 Luger uses the same mag whether for 7.65Para, or 9mm Para. My other handguns in 7.65Para also have no problems using 9mm mags.

Didn't the German military get offered the 7.65 only to ask for a larger diameter bullet? If so, necking the case up could've simply been the easiest way to meet that request.

About 1/4 of the way down the PHD did offer this bit of wisdom:
"Nosedive is an inherent problem in most single stack magazines. Even straight-walled cartridges nosedive, but cartridge taper makes it worse. Nosedive is less problematic in double column magazines, but it depends on specific magazine designs."

All the testing involved a 1911 with a Chip Mc mag and a Diamond Back, sounds a little inconclusive to me.
A solution looking for a problem?
However I lack a PHD.

My guess would be so that the case bottoms out in Sub gun chambers (which can get sloppy if they've had a lot of rounds through them) and can be extracted easily from very hot subgun chambers....as the taper might leave less surface area of the cartridge against the chamber.....just a guess.

quote:

Originally posted by jimmy123x:
My guess would be so that the case bottoms out in Sub gun chambers (which can get sloppy if they've had a lot of rounds through them) and can be extracted easily from very hot subgun chambers....as the taper might leave less surface area of the cartridge against the chamber.....just a guess.

Were any sub-machine guns in existence when the 9mm parabellum was designed?

Not that I know of.
The 9mm P came out in 1902-1903 and was adopted by the German Navy in 1904. It took the Army until 1908 to catch up, but it did get them the improved coil spring action.

quote:

Originally posted by jimmy123x:
My guess would be so that the case bottoms out in Sub gun chambers (which can get sloppy if they've had a lot of rounds through them) and can be extracted easily from very hot subgun chambers....as the taper might leave less surface area of the cartridge against the chamber.....just a guess.

your guess is correct. A cone shaped cartridge can be pulled easier after fireforming in a chamber then a one with a cylider shape.

The first pistol cartridge fired sub gun was the Italian "Villa Perosa". What we know as sub gun today has not been known before the introduction of the Bergmann 1918 SMG.

quote:

Originally posted by OTD:
your guess is correct. A cone shaped cartridge can be pulled easier after fireforming in a chamber then a one with a cylider shape.

That seems pretty obvious and I’d bet a nickel that that was the reason for the strongly tapered case of the 7.62×39mm Soviet cartridge. The case design doesn’t matter as much when clean ammunition is used in a clean chamber, but add corrosion, firing residues, environmental mud/dirt/sand/etc., then ….