Talking about the 7.5 FK. That is a lot of cartridge and needs a bigger gun. Not sure that that is the way ...

I agree.  The 7.5x27 FK is a much fatter cartridge than 4.6x30 HK and 5.7x28 FN, which would substantially reduce magazine capacity relative to the smaller rounds.

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.

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.