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

That looks great man.

Stock wise, theres a couple realllly light options.

Personally I'd love to see a Pic rail adapter to use the polymer B&T MP9 stock:

A close second (5.36oz + ~3oz mount) is the JMAC customs SS8:

That should put stocked weight at ~5.3lbs. 

Yeah I'm a fan of the jmac and the mp9 stock would be even better in some cases.

This said, due to the nfa I can't "stock" this gun.

Also, OG tailhooks are completely unobtainable right now which shaded my decision.

(As did the sheer cost and availability issues of my original plan which was to do an ACR brace)

Eventually this gun will get a different ass end but for now this definitely works (other than my dot I bought being 6 inches high at 5 yards when I took it out for initial break in lol)

I am actually coming back to 7.5x27 for cartridge and take it from there.