So how about an artillery Luger with a stock?

It's semi-auto, so it's a stocked pistol. Or carbine. Or SBR. 

At the time they were fielded, they were an improvement versus short (for their time) bolt-action carbines for close-quarters combat.
The SMG hadn't even been invented yet.
The Germans were just figuring out how to make Maxim MG's man-portable and had a concept of firing them from a standing position.

Some authors credit the Artillery Lugers and C96's as the first PDWs. I think the concept evolved over time. As mentioned earlier, it just depends on what your definition of a PDW is. I think it took a while for militaries and small arms developers to really put a finger on what they wanted the PDW concept to be. Everyone knew they wanted something bigger/better than a pistol, but smaller than a carbine. They wanted a weapon that could be stored out of the way on a person whose primary responsibility was not to fire their individual weapon. It took decades to figure out what that should be.

Interesting developments happened in the meantime, such as the invention of the SMG (which would initially seem to fit the bill), but there was still a demand for more compact weapons such as the Mauser M712 Schnellfeuer (1932).

Hell, even the US M1 Carbine fits into the dialog somewhere, only because of the concept of how it was intended to be issued. It was envisioned to be the TOE (Table of Organization & Equipment) replacement for the M1911A1 pistol, a small carbine to be carried (slung) in lieu of a holstered pistol. That's not what really happened in the field, but it looked good on paper (and in the accounting office, since it cost less). In my opinion, the M712 was the closest concept to a modern PDW available at the time (WWII).

The assault rifle revolutionized small arms development for infantry, but the niche of the PDW concept still wasn't fleshed out. After WWII, Czechoslovakia, Poland, and Russia all worked on pistol-caliber designs which were select-fire and able to be conveniently carried on one's person with an optional stock. As I alluded to earlier, I think the Czechs and the Poles were really the first to get it right. They just couldn't make them really lightweight.

This is really it right here. The M1 Carbine was small and light for its time. A lot of SMGs from the 30-50s, such as the Thompson and Uzi, weighted about twice as much. The modern concept of a PDW is essentially the MP5K, MP7 and P90. The point was to replace 9x19mm as the standard NATO sidearm, and have PDWs for vehicle crew members, pilots, a secondary weapon that is still small and light but superior to a pistol, and other niche uses. 9x19mm prevailed, which killed a lot of the momentum.

.300 Blackout seems to be killing off the SMG and PDW for special forces looking for a quiet primary weapon. There is still a small niche for these things, but not really much of a market for much more. The MP7 more or less has this one covered. The CZ Scorpion is a bit big, even if you get a smaller barrel it has the mag located in front of the trigger. May as well add another 2-3 inches and use a rifle.

Likewise, it is very similar to the term "carbine". Back in the 40s, the 18" M1 or the 20" SKS was considered a carbine. Then 14-16" became "carbines". Now, the standard barrel size is 14-16. A "carbine" these days is 9-12" really.

An M2 carbine shortened to 10" bbl, in a modified M1A1 stock would have been interesting.

I also wonder if the above in 5.7 Johnson/Spitfire would perform well.

On this topic, because I have a lot of time behind a lot of these systems, the mp7 in my eyes rains supreme for its ability to be quiet also. 300blk out of an 8" ar even with a can and subsonic will ring the shooters ear without ear pro. Quieter than supersonic, yes. But not as quiet as 4.6 or even most 9mm weapons.

Now, I would love to see an mp9 system in a 5.7 chambering. Subsonics aren't hard to do, and most micro 5.56 cans work well enough to make it sound like any suppressed 22 (go figure..)

I think they cut a bunch down in that Enforcer confit during Vietnam.

Yes, they were modified by individuals in-country.

Thanks for all the info and replies.

For further reading, this is probably the best article to date on PDW's:

http://www.quarryhs.co.uk/PDWs.htm

Tag

I agree, I think the MP9 in 5.7 would be the hotness.

In terms of subsonic performance, the R&R 55gr Copper Hollowpoint is very impressive. .22 Quiet, expands to .765" and penetrates 12".

Video

And the 34gr Supersonic load is also quite spicy for a 350 ft/lb pistol round that weighs 1/2 as much as a 9x19:
Video


With both of those loads paired with a 3lb MP9 Micro rifle and a suppressor... pretty handy PDW or sidearm.

I love my PS90s but FN really cheaped out with the blowback action.  The reason HK went with rotating locked breach is to reduce size and mass.  Any round can be made to operate on blowback action if you up the mass of the bolt.  That's why the P90's lead sled bolt makes as much noise going into battery as a suppressed 9mm.

Just because a gun is blowback does not make it "cheaped out".

That is the main reason it is used, very easy and inexpensive to manufacture.

It's also more reliable when it comes to pistol calibers, and simpler to service.

It's used because it's reliable.

Is a hi point more reliable than a glock?  No.  Blowbacks are not more reliable.  They are more sensitive to different types of ammo and feeding can be more problematic than tilting barrel locked breech designs.

As mentioned, blowback gives you more perceived recoil, increases weight, increases report of action, increases force needed to charge.  The only reason to use it is because it is much less expensive to manufacture.

I believe the MP7 requires Armorer level competence to work on the gas system:

"Interestingly enough, unlike the G36 and HK416, maintenance of the gas piston is not to be completed at the user level. Instead, it is strictly an Armorer responsibility, requiring a couple of specific tools to gain access to the gas piston. The photo below shows the gas piston, the parts that retain it, the removable hand stop that protects it and the recommended cleaning/maintenance products, FIREClean and the maroon Scotch-Brite (which is the recommendation for all HK piston driven weapons)."

http://www.hkpro.com/forum/teufelshund-tactical/197195-notes-mp7a1-armorer-course.html

As for the Blowback operation of the P90, the gun is extremely simple to work on and reliable. Even the guys who thought the 5.7 = eye aids commented favorably on its reliability.

It was a PDW designed for dudes who don't shoot or do weapons cleaning regularly to have a compact, reliable tool for hosing down commies.

I'll have to dig up the BattleField Vegas report on FN firearms, but I seem to recall their P90's were lasting a long time.

That's not saying too much. I believe those specific tools are 2 different size Allen wrenches and a flat head screwdriver. HK requires that you be an armorer just to disassemble a burst MP5 trigger group (which is admittedly more complicated).

Yeah the tools are hopefully not that restricted.

But later in post #39 of the thread:
"The recommendation from training and the manual is 500 rounds between cleanings, to include the gas piston. The recommendation for replacing the gas piston rings with signs of underfunction or between 15,000 to 20,000 rounds; closer to 15,000 is the majority of your shooting is suppressed."

Which means that every 500 rounds you would need either an Armorer or access to the special tools/knowledge needed for the Gas system of the MP7.

So when the other user commented about the P90 being a blowback = highpoint, this one of the huge reasons why - simplicity of user maintainence. The P90 is basically a simplified blowback AUG ie nearly caveman complex to clean and maintain.

Blowback has disadvantages in the P90 (inability to shoot heavier, higher power rounds that the FsN can fire like the 50gr Nosler BT from Elite.) But there are advantages as well, and it works quite well for most loads 40gr and below, as well as the 55gr subsonics.

You're comparing pistols, which can also be susceptible to limp-wristing, and HiPoints are arguably stone reliable unless they fall apart.  But that's a quality issue, not an operating system issue.

How about the CZ Scorpion, HK UMP, B&T, P90, practically every other mass produced SMG out there besides the MP5, MPX or Kriss?  Do they all do it for cost?  The MPX is not the most reliable firearm, the MP5 is a boat anchor compared to its modern competition, and the Kriss, while more controllable, is more difficult to charge and is large, heavy and awkward.
I have a feeling you've not handled or shot many of these...

As to your point of bolt closing noise, a DI AR15 bolt closing is upwards of 120db at the port.  If you don't believe me, put your ear next to the port and hit the bolt release (unloaded obviously).

The only one of your points with merit is the difference in perceived recoil for two similar firearms of the same caliber, but cartridges like 5.7 and 4.6 impart so little impulse into the bolt that the bolt mass is tiny in comparison to even a 9mm blowback SMG.

124gr 9mm 1200fps = 21.24  lb*ft/s
32gr 5.7mm 2300fps = 10.51  lb*ft/s

Dividing that number by your bolt mass will give you a rough idea of the initial bolt speed.

Ultimately that means that for blowback operation, with equivalent springs, the 5.7 could get by with half the bolt mass of an equivalent 9mm firearm.

His entire premise is ridiculous.

probably not everyone's definition of a PDW, but I've been looking at an AR platform that would enhance the hit quality over a pistol, easily and inconspicuously transportable in a vehicle.... my criteria was to produce a short AR platform using standard configuration bolt carrier and buffer assembly using a LAW stock adapter with a 7" upper...at this point my attempts to reduce the muzzle flash have not been successful.... I've been told that the NATO SS109 has a reduced flash signature and will try to obtain some test rounds... possibly some hand loads near the burn rate of H322...it is on the back burner and now sports a 10.5" upper.. I need to get some chronograph data to compare the 7 to 10.5..
also playing with a 7" 9mm AR...

I actually own most of the SMGs and have shot all of them, and yes of course the UMP was designed to be less costly to manufacture than the MP5.  The MP5 is a boat anchor?  That's a new one. Regardless, it wouldn't be due to the action.

Shooting the blowbacks vs the locked breech, especially the roller locked designs like the MP5 is night and day.  Definitely like the impulse of my MCX over my scorpion, but prefer my MKEs over the MCX.  The KRISS is overhyped snake oil but that's another thread... I have had 3 PS90s (still own 2) and though recoil is very manageable, when doing double taps and Mozambiques, having a roller delayed action would definitely help.

We could continue to argue about reliability but let's just for the sake of argument say they are both acceptably reliable and there are plenty of weapons with both operating systems to make that argument.  What can't be disputed is:

Blowback results in a heavier weapon, everything else being equal.

Controllability is lower with blowback.

So why do manufacturers use blowback?  I've spent a fair amount of time as a ME and production engineer, answer is pretty clear to me.  A PDW by definition should have a small form factor and highly portable.  I would have preferred a PS90 with a locked breech (and better less rounded grip), ymmv

I think the MP7 is the best PDW for anyone requiring a holster-able (possibly secondary) weapon, and the P90 is best for those who just need a PDW that is smaller than the most compact assault rifles, but only require that it be slung or able to easily go through an armored vehicle hatch with them.

If I could only pick one for my entire military's PDW needs it would be the MP7.
That's probably not going to happen though. It will likely remain a specialists' weapon.

MP5SD's must be cleaned every 300 rounds (10 mags) and you don't hear complaints about that, because they're only in use by specialists.

Here's a chopped M2 Carbine in Vietnam.

It's really difficult to know if you're buying ammo with flash retardant on the commercial market, unless you have some good reviews where it's been tested. Yes, if mil-spec it will have it.
I suggest employing an open-ended flash suppressor with prongs as long as you can tolerate. AAC BlackOut, Smith Vortex, B.E. Meyers 249F

What's the length of the 7" AR folded? And extended?

SpydercoMonkey... 17 1/4 and 24 1/2 with an A2 flash hider installed

KitBuilder... I tried to consolidate a YHM solid tube fore end to use as a flash can with the test of a 3 prong A1 and A2 flash hiders... the fender washer did a pretty good job of noise projection down range, but still had noticable flash... the LeVang did a pretty good job with the 10.3"... I need to chronograph both barrels to make a final decision... thanks for the comments

Just don't try that setup with a comp/brake

Thanks! I would say that is certainly compact enough to qualify as a PDW, and given SOCOM's recent solicitation for a PDW on .300blk that is between 17"-15" folded, you're in good company

My .45 is fairly nice and compact until you stick a fully loaded GG mag in it

When I had the skeleton stock on it, it was right at 15" folded. (and  would fire while folded...)









Now I'm focusing on putting some rounds through this thing, I think the last tweak is going to be opening up the front of the top cover ejection port to keep from occasionally snagging brass in a stove-pipe manner.

For one of my next projects I was thinking about a folding .300blk (or 5.56) similar to the FMG/FPG above that would fold with a loaded mag into a ~11" x 6" x 1.5" package and spring open in a similar manner, ready to fire.

ooooh!

That sounds great to me! Please keep us posted on how that comes together.

Would 17 3/4 also qualify?

Given that the FN P90 is 19.9" OAL, I would have to say yes. Likewise the Krinkov is also 19.375".

Which really gets back to the question of, what defines a PDW?

The original goal, of penetrating soft body armor is not really definitive, given that virtually any steel core projectile will achieve that; Buffman's testing of 1950's era steel core 9mm showed that it could defeat two IIIA vests stacked on top of each other. Likewise, the Russians have AP 9x18 Makarov ammo, and KTW even made an AP .25 ACP.

The unifying goals that all PDW's seem to share, is that it is a) a weapon substantially more compact then a rifle b) that is designed to defend against a surprise attack by men armed with rifles with improved hit probability than that offered by a conventional handgun.

Given that bullpups are 26" OAL, but are not PDW's, the OAL length must be shorter than that. I would say the Krinkov/ P90 set the practical limit at 19.9" - roughly the width of a man's shoulders.

In terms of improved hit probability against men armed with rifles, that covers a pretty wide range:

Specialized pistols designed for advanced adversaries:




Stocked Pistols:




Micro SMG's:




Purpose Built PDW's:






Chopped Rifles:




TL;DR - if it's below 20" OAL, and is designed for defense against men armed with rifles, it likely qualifies as a PDW.

follow up to my 7" folder quest.... I was able to greatly reduce the muzzle flash by going to hand loads with H322 propellant... not visible to shooter in daylight using a flash can, LeVang linear, 3 prong or A2 flash hider... the H322 loads are with 69 Sierra Match Kings, so I should get some pretty good accuracy