"nincomp

I think that the concern is that civilians would try to chamber the new rounds in old 7.62x25 firearms....

I wonder if Max or some other knowledgeable person could explain why the Soviet Union moved away from this round."

I'm no expert. My understanding was the 7.62 x 25 was a fairly powerful for a side arm. Hence it required a strong hand gun action to use it. The 9x18 being a much milder cartridge didn't need as beefy an action to contain it.

Hand guns are probably the least important weapon on the battlefield after bayonets. Switching to 9x18 allowed the Soviets to produce a simpler side arm. 

7.62 x 25 was a good round for submachine guns. With the introduction of  the AK series of weapons the USSR moved away from submachine guns.

If you're not changing the specs and raising operating pressure you're not actually doing anything worth doing.

That's kinda the whole point here, no amount of rearranging the deck chairs on the titanic of convention small cartridge design is going to give you the performance we want or that cartridge and loading would already exist.

Good suggestion.  I did not realize that it ran at 55,00psi until you mentioned it and I looked at it more carefully.  Previously I had thought that it used 9x19 pressures.  I think that this would be a good solution for a close range PDW, with decent armor penetration if it used a relatively smaller hardened core.  It is just when the desire is for something useful at 300m or so that I see a problem.

graylion said:

more civilian market. also, it doesn't make a huge amount of difference and saves the odd civilian casualty, so why not?

Increase the OAL to 38 mm for a pointy bullet and incompatibility with existing mags. Will be at the limit of grip size though, so it's probably better off keeping the OAL and dropping the case to 22 mm or so and upping the pressure dramatically. 

roguetechie said...

If you're not changing the specs and raising operating pressure you're not actually doing anything worth doing.

I agree.

roguetechie said:

That's kinda the whole point here, no amount of rearranging the deck chairs on the titanic of convention small cartridge design is going to give you the performance we want or that cartridge and loading would already exist.

Yup 9x19  +P+ and 5.7x28 are the two ends of the spectrum. There really is no point to adding  a third indifferent round with limited lethality. Increased OAL for the 9x19 for a pointed steel projectile might be interesting but not enough that anyone has actually done it. Even the Russian 7N21 has a round point despite being a dedicated AP round. Probably to promote feeding with a more-or-less straight cased round. 

roguetechie said:

...no amount of rearranging the deck chairs on the titanic of convention small cartridge design is going to give you the performance we want...

Is that the royal "we" or do you have a mouse in your pocket?   8^)

There are diverse opinions here about what performance a PDW should have.

Red7272 said:

roguetechie said: That's kinda the whole point here, no amount of rearranging the deck chairs on the titanic of convention small cartridge design is going to give you the performance we want or that cartridge and loading would already exist. Yup 9x19  +P+ and 5.7x28 are the two ends of the spectrum. There really is no point to adding  a third indifferent round with limited lethality. Increased OAL for the 9x19 for a pointed steel projectile might be interesting but not enough that anyone has actually done it. Even the Russian 7N21 has a round point despite being a dedicated AP round. Probably to promot:e feeding with a more-or-less straight cased round. 

I agree. I'd like a more powerful round that actually is a carbine round and not a pistol one. A combination of several technological advances gives the option of doing that:
 

• modern powders, allowing faster combustion and shorter barrels
• the understanding of combustion, leading to short and thick cartridges allowing shorter barrels
• higher cartridge pressures
• polymer or hybrid casings for even higher pressures  
• the P90 style mag

this allows for a much smaller cartridge than .30 carbine to have similar E₀ and be able to be used in a ridiculously huge "pistol" that can be turned into a carbine/SBR by virtue of a folding or detachable stock.

stancrist said:

Is that the royal "we" or do you have a mouse in your pocket?   8^) There are diverse opinions here about what performance a PDW should have.

A lion ;)

Let's say 9mm has ~500J and the new 6.8mm Magnum somewhere north of 3kJ. A carbine round that sits between 1 and 1.5 kJ would seem to be sensible. 

graylion said:

Let's say 9mm has ~500J and the new 6.8mm Magnum somewhere north of 3kJ. A carbine round that sits between 1 and 1.5 kJ would seem to be sensible.

It does not seem sensible to me to set a purely arbitrary figure for muzzle energy.  What I think would be sensible is to decide what performance is wanted, then design the gun and ammo to achieve that performance.