To what range though?

Also when it comes to pdw's specifically, the thing we're going to fight the most is the need for long and finely ballistic shaped projectiles.

Put simply the mechanism that modern body armor defeat depends on can be boiled down to a simple joules per mm2 squared impact energy formula that almost exclusively favors a long skinny pointy and fast projectile.

Other than high explosive there's not much in the way of methods to get around this tyranny.

There's a pretty narrow solution space in which you can generate the necessary prerequisites all of which involve the above stated solution.

graylion said:

stancrist said: Honestly, I'm not sure if I am okay with that layout.  I've handled -- and once mocked up -- a shoulder rig for the SWD M11/Nine, a compact 9mm SMG, but am a little skeptical about the feasibility of holster carry for such a bulky (50mm wide) weapon.

Gods that thing is huge. Once it starts selling I am sure somebody will make a thigh holster for it. Then we will see. But I more meant the Elbonia thing.

I'm okay with the Elbonia thing.  Actually, I've been trying to convince them to modernize their paratroops:  'Jetman' Flies Jetpack Through Italian Alps - YouTube 

graylion said:

Anyway, what other options? since we are developing the cartridge, we can go for a shorter COAL, but also, the bigger cartridge will make this weapon even higher.

For a cartridge of the size and power you propose, the only other option I can see is a conventional SBR, which has its own dimensional issues.

Um, might want the Es to get working backup parachutes first.

What's a backup parachute?   

Also called a reserve parachute. In this case probably a pistol.

stancrist said:

graylion said: Anyway, what other options? since we are developing the cartridge, we can go for a shorter COAL, but also, the bigger cartridge will make this weapon even higher. For a cartridge of the size and power you propose, the only other option I can see is a conventional SBR, which has its own dimensional issues.

For a cartridge of the size and power you propose, the only other option I can see is a conventional SBR, which has its own dimensional issues.

see, of that I am not sure. I recon I need ca 1.6cc cartridge volume. Back of the envelope says that can be done in a very chubby cartridge (which is good for combustion) which is no longer than 5.7x28, and has a base diameter of ~12mm. This could be used in P90 like mags or possibly singe stack mags - widening to double underneath the handle? Just throwing ideas out.

I'd use a polymer case. I am thinking about a very light bullet with a very pointy tungsten or tungsten/steel penetrator, maybe an aluminium body and copper drive bands and a 7N21-like construction regarding discarding the core. I can get this pretty fast (~3800 fps) but velocity drops quickly. At 150 yds we are down to ~3000 fps, which might still pierce armour. 

I agree, that a classic rifle layout as you show in your pictures is probably counter productive, I'd prefer the P50 layout. A bullpup layout has fundamentally the same problem.

OTOP if this can be done in a 5.7x28 more brutal version, I'd be tempted to go down that route

I am sure something like 6.5 CBJ would work best. from 12' barrels it can group 13 inches at 300m. Is that reasonably good?

graylion said:

stancrist said: For a cartridge of the size and power you propose, the only other option I can see is a conventional SBR...

see, of that I am not sure. I recon I need ca 1.6cc cartridge volume. Back of the envelope says that can be done in a very chubby cartridge (which is good for combustion) which is no longer than 5.7x28, and has a base diameter of ~12mm. This could be used in P90 like mags or possibly singe stack mags - widening to double underneath the handle? Just throwing ideas out. I'd use a polymer case. I am thinking about a very light bullet with a very pointy tungsten or tungsten/steel penetrator, maybe an aluminium body and copper drive bands and a 7N21-like construction regarding discarding the core. I can get this pretty fast (~3800 fps) but velocity drops quickly. At 150 yds we are down to ~3000 fps, which might still pierce armour.

Perhaps it would work.  The trouble is, it's rather difficult -- for me, at least -- to really evaluate a gun and ammo that cannot be handled or fired.

However, I do like the basic concept of a PDW with P90-type magazine.  Similar weapons have been proposed before, but only in pistol calibers.

Italian "Bullpup" Submachine Gun Concept Unveiled, Futuristic Electronic PDW? -The Firearm Blog

Marshal Arms Pistol (securityarms.com)

stancrist said:

Perhaps it would work. The trouble is, it's rather difficult -- for me, at least -- to really evaluate a gun and ammo that cannot be handled or fired. However, I do like the basic concept of a PDW with P90-type magazine. Similar weapons have been proposed before, but only in pistol calibers. Italian "Bullpup" Submachine Gun Concept Unveiled, Futuristic Electronic PDW? -The Firearm Blog Marshal Arms Pistol (securityarms.com)

Yup, have seen the top one, not the bottom one. Are you willing to proceed on the basic assumption that P90 style mag works and we'll go talk about other details?

The Hill SMG of 1952: