graylion said:

that depends. if the rest of the squad is carrying 6.8mm weapons, I'd move to $PDW calibre$ kind of weapons for the non riflemen. How many different weapons one wants in that calibre is a different question. My thinking is still 1, but maybe 2 or 3 (including the pistol for staff officers).

Which is perfectly reasonable. I fully agree.
If it has to be the same weapon is a different matter though. Why not use something like a carbine that is optimised to get the last bit of performance from the PDW caliber and handles like its bigger brothers.
A PDW optimised for easy of carrying and use for non infantry. And a pistol for whoever wants or needs it.

Currently militaries often use several different 5,56 weapons. Several different 9x19 used to be the case in the past. Why not do it the same way with a PDW carbine.

stancrist said:

Just happened to come across this 2021 article which echoes my thoughts on the subject...

I forgot to make one point in my previous longer post.
I read the article and the points I made previously and this addition apply to both your arguments and the article.

If penetration is such of an issue there still is no need to use SBRs or carbines. This again is where the 7.5 BRNO comes in. A cartidge that delivers the same KE from a pistol sized platform as 5,56 does with a 10" barrel is proven possible by it. Why not simply apply it to the SCHV PDW concept of the 5.7 and 4.6? Optimise a cartidge of similar power for penetration. This way the penetration of a 5,56 SBR could be put in a very handy and compact PDW.
Of course it would lower ammo count and shootability compared to 5.7 pr 4.6 weapons. But 5,56 SBRs also don't have this.

With the advent of 6.8 and a de facto return of the battle rifle IMHO a PDW and a PDW cartidge make more sense than ever. 5,56 weapons can be made quite small and light and still stay more or less usable. With 6.8 this is as much the case as with 7.62.

schnuersi said:

If it has to be the same weapon is a different matter though. Why not use something like a carbine that is optimised to get the last bit of performance from the PDW caliber and handles like its bigger brothers. A PDW optimised for easy of carrying and use for non infantry. And a pistol for whoever wants or needs it.

I am uncertain about the carbine - who gets it? HE slingers and machine gunners? Snipers?

schnuersi said:

       stancrist said: I'm not talking about the current situation, but the near future when 6.8 ADVAP ammo is planned to be standard issue for infantry.

But 6.8 is not even suitable for carbine use. Let alone SBRs. If it is done the KE will suffer as will penetration wich nullifies the penetration advantage this round offers.

The US Army apparently does not share your opinion, because the XM5 "rifle" with its 13-inch barrel is, at best, really just a carbine, if not actually in the SBR class.

schnuersi said:

Actually I am pretty amazed by what I percieve as cognitive dissonance of the people who are arguing for 6.8 "death ray" while on the other hand for arguing for 5,56 and against 7,62. In all those years we had several discussions in this forum about the merits of SCHV and why full power rifles are unsuitable as infantry armament. All of a sudden full power isn't even enough anymore.

I am not arguing that the 6.8 "death ray" should be adopted.  I am only saying that if the small arms used by infantry riflemen and machine gunners can defeat modern hard body armor, then it seems to me that a future PDW should also penetrate the same armor (except at much shorter range).

graylion said:

       stancrist said: if only because the pistol is universally considered necessary and nobody wants a 4.6 or 5.7 handgun.

Why? 5.7 proved quite effective when used by that guy who shot up an army base.

9mm has also proven quite effective in similar mass shootings, so if that's the basis for pistol caliber there is no reason to change.

stancrist said:

graylion said:        stancrist said: if only because the pistol is universally considered necessary and nobody wants a 4.6 or 5.7 handgun. Why? 5.7 proved quite effective when used by that guy who shot up an army base. 9mm has also proven quite effective in similar mass shootings, so if that's the basis for pistol caliber there is no reason to change.

Not my point. I was attacking the statement that "nobody wants a pistol in 5.7"

stancrist said:

The US Army apparently does not share your opinion, because the XM5 "rifle" with its 13-inch barrel is, at best, really just a carbine, if not actually in the SBR class.

And yet it is 3" longer (36") than an M4 - so I am calling BS. 

I have been playing with a cartridge that would kind of do the job on defeating Lvl IV armour out to 100m, But a pistol cartridge it ain't. A carbine catridge sister to the .277 Fury? Yes.

This thing will not fit into a handgrip unless it is a single stack, so P90 style mags it is, even for the pistol :(

Bullet Aluminium with steel core:

http://www.geoffrey-kolbe.com/cgi-bin/drag_working.cgi?unit_length=mm.&weight_unit=grains&bullet_name=GLS+PDW+II&re_calculate=yes&boundary_layer=L%2FT&entry=return&diameter=7.51&length=21&nose=14&meplat=0&drive_band=7.8&base_diameter=5&angle=8.5&boat_tail=5&secant_radius=5.7&weight=49.2&density=5.2

And, assuming our PDW has a 200mm barrel, I get this (assuming same pressure as military load for .277 Fury). 

Google Docs

7.5 Graylion Load R24.png

Read more from Google Docs

stancrist said:

I am not arguing that the 6.8 "death ray" should be adopted.  I am only saying that if the small arms used by infantry riflemen and machine gunners can defeat modern hard body armor, then it seems to me that a future PDW should also penetrate the same armor (except at much shorter range).

If you want to maximise penetration above all else in a pistol/PDW, then see the 6.5mm CBJ.

schnuersi said:

If penetration is such of an issue there still is no need to use SBRs or carbines. This again is where the 7.5 BRNO comes in. A cartidge that delivers the same KE from a pistol sized platform as 5,56 does with a 10" barrel is proven possible by it. Why not simply apply it to the SCHV PDW concept of the 5.7 and 4.6? Optimise a cartidge of similar power for penetration. This way the penetration of a 5,56 SBR could be put in a very handy and compact PDW.

With the advent of 6.8 and a de facto return of the battle rifle IMHO a PDW and a PDW cartidge make more sense than ever.

I fully agree.  The only reason to use existing 5.56 SBRs for the PDW role is because the guns and ammo are already in the inventory. 

But if the funding is available, a purpose-designed PDW in a caliber that gives the desired penetration, does indeed make more sense.

Well the XM5 might be a carbine for .30 cal or full power rifles but its size and weight is not in the same class as the common 5,56 carbines.
With the supressor fitted, which seems to be the intended way of use, the XM5 is about the size and weight of a G3 battle rifle.
Its so large and heavy that its completly unsuitable as PDW or secondary weapon.

stancrist said:

I am only saying that if the small arms used by infantry riflemen and machine gunners can defeat modern hard body armor, then it seems to me that a future PDW should also penetrate the same armor (except at much shorter range).

IMHO that depends if this is a realistic goal.
From my point of view for a PDW carryability is the primary concern. Followed by usability. If such a level of penetration at 100 m is possible without compromising the carry- and usability that is fine.

stancrist said:

9mm has also proven quite effective in similar mass shootings, so if that's the basis for pistol caliber there is no reason to change.

Yes but 5.7 has less recoil, flatter trajectory and larger capacity magazines. Which makes it the better choice.