stancrist said:

which would substantially reduce magazine capacity relative to the smaller rounds.

The handguns in 7,5 FK have a magazine capacity of 15 rounds. Which is what a typical 9x19 service pistol has. So it can be safely assumed the capacity of a larger magazin is also comparable. Which would mean a 30 rds magazine is of reasonable size.

stancrist said:

Also, the 7.5 FK is considerably heavier, with bullets which weigh three times as much. I don't see a logical reason for advocating 7.5 FK as a military PDW cartridge.

IMHO the 7,5 FK adresses the criticism or potential shortcomings of the 5,7 and 4,6 PDW cartidges. Lack of power and low mass projectiles. The 7,5 FK indeed is more powerfull. Which means its in the performance range of 5,56x45 from SBRs. This also offers potential for improveing in armor piercing performance. While the large and heavy ball type bullet has significant stopping power.
Yes the cartidge is heavier than the the smaller two. But there is a price to pay. Its either performance or weight.
I have no idea how the 7,5 FK would perform in a full auto weapon. I guess its less controllable than 4,6 or 5,7. More like 9x19.

schnuersi said:

The handguns in 7,5 FK have a magazine capacity of 15 rounds. Which is what a typical 9x19 service pistol has. So it can be safely assumed the capacity of a larger magazin is also comparable. Which would mean a 30 rds magazine is of reasonable size.

Yes, like I said, magazine capacity of 7.5 FK would be reduced relative to the smaller cartridges:  15 rds vs 20 rds for a flush mag; 30 rds vs 40 rds for extended mag.

schnuersi said:

IMHO the 7,5 FK adresses the criticism or potential shortcomings of the 5,7 and 4,6 PDW cartidges. Lack of power and low mass projectiles. 

This also offers potential for improveing in armor piercing performance. While the large and heavy ball type bullet has significant stopping power.

I have no idea how the 7,5 FK would perform in a full auto weapon. I guess its less controllable than 4,6 or 5,7. More like 9x19.

Considering velocity and bullet weight, full-auto controllability should be more like .30 Carbine.

And .30 Carbine Ball does not have a particularly spectacular reputation for stopping power.

My main concern is actually size and thus carryability of the gun.

I have no reason to think that a 7.5 FK PDW would be any bigger than the MP7.

stancrist said:

Considering velocity and bullet weight, full-auto controllability should be more like .30 Carbine.

Controllability also depends on the weapon and its layout not only the impulse of the round.
It would have to be tested how controllable a modern gun is when firing such ammo in full auto.

stancrist said:

And .30 Carbine Ball does not have a particularly spectacular reputation for stopping power.

No but the .30 carbine ball is a legacy design round nose bullet. The 7,5 FK has been designed with stopping power in mind. It is advertised as having better effect/stopping power than .357 mag.
How a military loading would look and work is unclear. I think the standard load for the 7,5 FK is not Hague/IHL compliant.
Same with an AP bullet. Depending on design it could be really good or not so much.

Never the less the 7,5 FK shows that SBR like performance from an handgun or PDW sized weapon is possible.

If something like the 7.5 FK would be considered, I wonder if the US would also consider non-traditional bullet shapes.  Various solid, fluted nose bullets are becoming increasingly common.   Is anyone aware of information on how similar nose shapes affect armor penetration and wounding?

schnuersi said:

Controllability also depends on the weapon and its layout not only the impulse of the round. It would have to be tested how controllable a modern gun is when firing such ammo in full auto.

Of course.  But, assuming guns which are the same except for caliber, full-auto controllability of 7.5x27 should be more like .30 Carbine than 9x19.

schnuersi said:

       stancrist said: And .30 Carbine Ball does not have a particularly spectacular reputation for stopping power.

No but the .30 carbine ball is a legacy design round nose bullet. The 7,5 FK has been designed with stopping power in mind. It is advertised as having better effect/stopping power than .357 mag.

Independent testing shows the 7.5 FK hollowpoint bullet produces a wound track similar to that of .30 Carbine round nose FMJ.

https://youtu.be/DTqu2MLoHEo?t=152

schnuersi said:

How a military loading would look and work is unclear.

That's because no one has seriously proposed -- let alone developed -- a military PDW in 7.5 FK.

What is clear is that COL limits a spitzer bullet to an ogive like that developed for .30 Carbine AP.

schnuersi said:

Never the less the 7,5 FK shows that SBR like performance from an handgun or PDW sized weapon is possible.

Right.  Just because something may be possible, does not mean it is practical or desirable.

nincomp said:

If something like the 7.5 FK would be considered, I wonder if the US would also consider non-traditional bullet shapes.

I doubt it.  In the seemingly unlikely event of 7.5 FK being seriously considered, I'd expect that a traditional (albeit rather stubby) spitzer bullet would be used.

nincomp said:

Various solid, fluted nose bullets are becoming increasingly common.   Is anyone aware of information on how similar nose shapes affect armor penetration and wounding?

I think there are YouTube videos of such bullets tested against body armor.

A new 'Krinkov Class' / 'SBR Class' PDW has been released. 

The Dissent (awful name) by CMMG. 

14.7" folded 

4.8lbs (probably 5-5.2lbs with light stock)

6.5" barrel in 5.56 / .300 BLK / 5.7x28

-->Pretty comparable weight and length to the MP7, with the ability to use 5.56 mags and ammo. Downside is not Holsterable, and no doubt tremendously loud. 

It's also slightly shorter with +1" of barrel length compared to the SIG Rattler, which is 16" folded with a 5.5" barrel. 

Action looks to be Direct Impingement, while deleting the traditional AR buffer tube.

Initial shooting looks pretty low recoil and easy to handle:

YouTube

New CMMG Dissent PDW First Shots

New for 2022, the CMMG Dissent is a lot of punch in a little package.Get cool swag: https://the-honest-outlaw.creator-spring.com Here is a link to donate to ...

I think a 7.5"-8" barrel could make a compelling Carl Gustaf / NLAW / Milkor companion for those not looking into a dedicated PDW caliber ala 5.7/4.6. 

I went a slightly different direction but got to pretty much the same place...

Mine is 5.56, has an 11.5" bbl and will soon be sporting a brake and blast can though it doesn't really need it because it already shoots extremely nice.

The foxtrot Mike fm15 is also a DI gun just like the cmmg dissent, though I think I like what cmmg is doing with the recoil springs better.

I do question the exact niche the cmmg gun is going for too...

Realistically with the 6.5" bbl and no brace or hinge in it's factory weight spec it's going to wind up substantially heavier once it's actually in usable configuration.

I believe the fm15 11.5 started out around 6 pounds but once I threw on the hinge, tailhook mod 2 magnifier and dot it's definitely not 6 pounds now.

It's still extremely light and handy but it's definitely no feather weight.

I wonder if cmmg did the sling qd point on the rear below the picatinny interface like foxtrot Mike did, that sling point is darn handy