gatnerd said:

As I've said numerous times, and echoing Tony's comments, where the PDW makes the most sense is for the 'HE lobber.' A infantry guy whose primary job is employing man portable HE weapons (40mm smart grenades, 84mm CG, ATGMs, MANPADS, etc.)

The important part here is "infantry guy". Yes he might need a PDW. But since he is infantry his needs don't really overlap with all the other potential PDWs users who are not infantry.
IMHO it really makes little sense to use the same PDW class weapon for the infantry users and everybody else. For example for the infantry users caliber comonality with the rest of the squad is a serious advantage. The training and mode of operation also would allow the infantry user to actially make use of the potential of 5,56. So a SBR of some sort of 5,56 PDW make sense for these guys. But it needs to be kept in mind that they are few in comparison. A special case.
To me it seems not the ideal solution to try and shoehorn a single solution based on the needs of a special few for everyone. This will ultimately lead to a similar situation as we currently have.
This is why I am advocating the infantry weapons for infantry and a PDW with focus on easy of carrying and use for anybody else.

gatnerd said:

For truck drivers / mechanics / cooks etc (the original use case of the PDW) I dont think its worth the hassle vs just issuing them a M4 or a pistol, as their probability of conflict is so low.

And if their propability of conflict is so low why should they carry unnecessarily powerfull and large (carbine) or allmost useless (pistol) weapons? The thing is if these occupations have to use their small arms something went wrong allready. So they need something that works best for them in such a situation.
The statement that the propability of conflict is low also seems questionable. The losses of the German Army in Afghanistan include a disproportionate number of non infantry and even non combat personel. This might be a theatre specific problem but IMHO theatres similar to Afghanistan are more likely in the future for the German Army and all NATO Armies. Regardless what is happening currently and all the politicians chiming about homeland defense. Once the situation in UA is solved other things will come back into focus. The world has not become a saver place. UN and NATO missions in LIC and COIN scenarios are still very likely. Even though we might not like it or want it.

gatnerd said:

As I've said numerous times, and echoing Tony's comments, where the PDW makes the most sense is for the 'HE lobber.' A infantry guy whose primary job is employing man portable HE weapons (40mm smart grenades, 84mm CG, ATGMs, MANPADS, etc.)

I have to disagree.  I think that a PDW of the types you propose for the "HE lobber" make little sense.

Weight of loaded MP9 + 3 spare mags is ~7 lbs.  A loaded CMMG + 3 extra mags would be over 8 lbs.

Note that in your examples the Ranger carried a pistol (weight penalty ~ 3.5 lbs) and the XM25 users didn't carry a secondary weapon.

The "HE lobbers" operate as part of a team, and their focus should be on maximizing effectiveness with their primary weapon systems,

As Tony said, the heavier is the secondary weapon, the less weight is available for grenades, so the less effective the grenadier will be.

IMO, a pistol is the best choice of secondary arm for troops equipped with multi-shot grenade launchers and the reloadable 84mm CG.

And "HE lobbers" with a disposable weapon like AT4 and Javelin, really should have a carbine/rifle for use after expending their missile.

PDWU? Personal Defense Weapon Upper, 11.5" barrel, with suppressor taking it out to 14.5". Figure to use an integral suppressor to keep length down.

Farmplinker said:

11.5" barrel, with suppressor taking it out to 14.5"

OMG, it feels like deja vu all over again!    

I always considered the XM177 to be the best looking M16 variant.  

schnuersi said:

       gatnerd said: For truck drivers / mechanics / cooks etc (the original use case of the PDW) I dont think its worth the hassle vs just issuing them a M4 or a pistol, as their probability of conflict is so low.

The statement that the propability of conflict is low also seems questionable. The losses of the German Army in Afghanistan include a disproportionate number of non infantry and even non combat personel. This might be a theatre specific problem but IMHO theatres similar to Afghanistan are more likely in the future for the German Army and all NATO Armies.

In order to propose a solution, we first need to know what the problem is. 

What caused those losses:  IED blasts?  Enemy fire?  Green on blue attacks?

Such information could make a big difference in what type of "PDW" is best.

And with planning for (near) peer war, PDW needs may differ from LIC/COIN.

stancrist said:

What caused those losses: IED blasts? Enemy fire? Green on blue attacks?

You are right. So I looked it up. Only superficially though.
The total losses of the Germany troops in Afghanistan are 59 KIA. The vast majority are by IED/suicide bombers. Losses to enemy fire are rather few. I counted six due to enemy fire. Three by accident during a firefight. Three by green on blue.
The green on blue have been two AFV crew and one mechanic. Shot while performing repairs and maintenance on a IFV inside the base.

stancrist said:

And with planning for (near) peer war, PDW needs may differ from LIC/COIN.

I am not really convinced it is. While LIC/COIN or HIC has conciderable influence on how infantry operates and what their engagement ranges are I don't really think this is the case with PDW use by non infantry personel. In either case we talk about self defense to maybe 100 m.
The target might make a difference but 5.7 and 4.6 have been designed with near pear HIC in mind so they will most likely work as intended in such a scenario. For LIC/COIN their single shot stopping power might be insufficient and their penetration to good so they are not the optimal choice. I really think it comes down to ammo used though. 

schnuersi said:

The green on blue have been two AFV crew and one mechanic. Shot while performing repairs and maintenance on a IFV inside the base.

No MP7 available?

EmericD said:

No MP7 available?

While performing repairs and maintenance on the vehicle, the mechanic and crewmen were almost certainly unarmed.

Even in the unlikely event each had an MP7 on his body, it would not have mattered because their focus was on the job.

EmericD said:

No MP7 available?

Apparently not. I don't even know if they where equiped with MP7.

stancrist said:

While performing repairs and maintenance on the vehicle, the mechanic and crewmen were almost certainly unarmed.

Yes, it seems like it.

stancrist said:

Even in the unlikely event each had an MP7 on his body, it would not have mattered because their focus was on the job.

The thing is alltogether there have been nine casulties. The three KIA plus six wounded. Of the three KIA not all where killed outright. Only one of them died on the scene. The short report i have read also mentiones a fire fight. So apparently after the initial supprise attack it came to an exchange of fire. The attacker apparently had been killed by guards who rushed to the scene and shot him with rifles. There is mentioning that the soldiers doing maintenance (more than the nine casulties) where outgunned by the attacker with an AK. That to me sounds an awefull lot as if they had pistols ready to use.
But to get anything more substancial I would have to look into some more detailed and most likely official.