I recently put together a 9mm AR, and I really like the set up. But with the magazine adapter, heavy buffer, and bolt, it is a pricey item to set up. Yet a 9mm blow back carbine seems like a fairly simple item to put together. A thread caught my attention, and I did some reading on the PPSH, and noted the simplicity of the action. It got me to wondering if  something similar could be accomplished with an AR 9mm. The main item of note was that the recoil spring was contained within the reciever. If an AR was set up similarly, it would open up the option of a folding stock or 9mm pistol with no stock.

Reading up on the PPSH, it was pretty clear that the Russians learned a hard lessons from the Finns, who employed the Suomi KP/-31 (a 9mm sub gun) to great effect. The Russians responded by ramping up production and use of the PPSH, which proved itself throughout the war. According to the accounts I read, the 9mm Finn sub gun was used heavily and played a pretty large role in their defense against the Russian invasion. It demonstrates the point that if your ranges are fairly short, a 9mm carbine can clean up, and having an intermediate rifle cartridge with a 500 yard range is overkill, but that's another topic.

Anyway, all of this is just an observation. A 9mm AR is probably a better system than any of the WW2 9mm sub guns. It is just somewhat surprising to me that given their history of performance and simplicity, it seems pretty tough now-a-days to get a well performing 9mm carbine.  

The PPSH 41. The excellent photos are care of this thread, and I thank him for the great write up and post he did.
http://www.m4carbine.net/showthread.php?32181-PPSh-41-Submachine-Gun


Overall, you can see the fairly compact size of the carbine.


Notice the size of the bolt and action. For a blowback action, could a bolt and recoil spring fit within the reciever of a standard AR? Then you could lose the buffer tube and then fold the stock. Just a bolt and a spring, no buffer or tube.



The recoil spring is captured in the receiver, and does not extend into the stock. Note the overall simplicity of the action.


Overall view of the action.

Blowback guns need a heavy bolt to work. In other words, the bolt has to be a certain weight.

One difference is the PPSH has a steel receiver as opposed to the aluminum of the AR. I think it would beat itself to death.

If you want a side folding, buffer free 9mm buy a M-11.

I did read that in use the PPSH was hard on it's buffers. It was an 8 pound carbine, so the frame was probably fairly beefy. The WW1 Bergmann German sub gun that lead to the PPSH was even heavier. The Marlin camp carbines had buffer issues too I recall, so perhaps the long spring and separate buffer in an AR helps in some ways.

At any rate, since it will finally be above 30 degrees this weekend for the first time in months, I think I'll be getting some range time this weekend.

It could be done, similar to the Uzi. Problem is the bolt would have to be redesigned and have a proprietary buffer spring. Simplifying it in design, but would substantially add to the cost.

Like the AK, the PPSh uses a heavy bolt with a channel for the recoil spring guide.  That bolt is heavier than a 9mm AR bolt, and the spring isn't exactly "light" either.  While the PPSh runs 7.62 Tokarev (a high power pistol round) as compared to 9x19mm, the balance between bolt mass and spring is pretty close.  There are "bufferless" 9mm ARs out there, but they are just not as common because one of the things that makes a 9mm AR attractive is the commonality with rifle-caliber ARs.  "Bufferless" 9mm ARs use a proprietary bolt and upper, and that makes the price point considerably higher.  In contrast, you can use ANY standard AR upper (figure $90) and any 9mm AR bolt (anywhere from $120 to $150) to build your "conventional" 9mm AR upper.

Yes, it's doable, and not all that complicated.  But for me, it's not worth all the extra fuss.

The commonality of parts that GHPorter discussed is probably the biggest driver for maintaining the typical ar9 bolt/buffer combo.  There's also the weight required to slow down the recoil of a blowback system. In order to remove the buffer tube/receiver extension on an ar9 you have remove the latter half of the bolt (weighted) and as well as the buffer (another 5-12 oz).  If you look at typical blowback smg designs (ppsh, m11/9, uzi) they all have heavy bolts to slow down recoil.  Uzi's and m11/9's use a telescoping bolt minimize the rearward length of the bolt...something you can't do with a milspec ar15.