RRA has a bufferless 5.56 AR
Gilboa has made a bufferless 9mm AR glock hybrid

This is my latest project.

What problems do you see coming up during the process?

I figure I need:

9mm bolt cut down much shorter.
Custom recoil spring system build to run in the gas piston area of the upper and attached to the bolt. HK style side charging concept in the future after a working design is made
Possibly another spring in the rear of the bolt for additional recoil control
A cap/side folding stock adapter fro the rear of the lower
Glock mag lower or magwell adapter


I can't be the only one that wants to build this.

You should probably check into what all is required to run a gas operated 9mm setup before you get too far into fantasy island.

Didn't POF just come out with one last shot show?

This. The demand for bufferless ar's is low anyway.

Aside from the cool factor of having a folding stock, there really isn't much of a point

Would you not consider looking at a Sig MPX?  Fire controls, grip, mag release, and charging handle like an AR.

You dont need gas. 9mm runs just fine on blow back.

Only reason you mess with the gas piston/tube area would be to put in a recoil spring in there.

As gor the Sig mpx and scorpion they are great but take different mags. I'm looking at a mp5 replacement that uses the same mags as the duty pistol. Mags that are cheap and already real common.

Thank you, that was more of the answer I was looking for.  My next question would be can you lessen the mass and substitute it with heavier spring tension?
Couldn't you adjust the back of the bolt to catch the hammer if fired when it isn't all the way forward?
Also Say with a non ramped bolt and a notched hammer couldn't you add a lip of metal under the firing pin/bottom of the bolt so that the bolt would have to be fully seated to make contact with the hammer?

Physics isn't my strong suit  

Spring tension will not substitute for mass in a blow back action.  However - what Mad-Machinist missed is that not all the weight of the bolt has to be in the upper.  Using the gas tube hole on the upper, you can run a connecting rod to weights that overhang or surround the bbl, and reciprocate w/ the bolt - kinda a reverse long stroke piston.  The slimmer the handguard, the longer that bolt mass will be.  Also makes it easier to add a forward charging handle, as you just cut a slot in the handguard and directly connect a charging handle to the forward bolt mass, albeit a simple handle would reciprocate.

This thread may give you some ideas, as a poor New Yorker behind enemy lines built himself a pump-AR that uses the gas tube hole for an op-rod, which is what you'd need to tie your forward bolt mass to.

Greg Carlson (Carlson's Comps) has a patent on a Pulse Recoil System that puts the op rod and spring forward of the bolt to eliminate the need for the receiver extension. It is a nice clever design. He is still looking for someone to license the patent for production, which should tell you about the size of the market.

Pulse Recoil Patent

No, happily not me, but indeed it's a well-built NY legal AR.

Did you consider putting the forward bolt weights on a track on the underside of the handguard, instead of riding on the bbl?  I agree, the connecting op-rod is weak, but is what PWS is using for their piston op-rod.  Of course, this morning I just read a thread about one of them breaking...  

http://www.ar15.com/forums/t_3_122/676545_Broken_and_Confused_PWS_MK_109___Ideas_.html

It would have been nice if the MPX took Colt/Uzi mags, that's for sure!

The man who perfects the forward action AR will make some serious coin.  PWS is getting close, if they can get their oprods to hold together.

I ordered 5 Uppers today to start playing with.

With a weight ring under the hand guard has me thinking about a guide rod/spring setup similar to a M11/10 setup.  Weight off the barrel and tracked on the hand guard loosely and using the guide rods to limit movement that may stress the rod  and springs to handle recoil.

While I am thinking about all of this I am thinking about how to assemble and disassemble for cleaning and maintenance.

With the larger rod I would have to remove the factory AR style charging handle.  I may look at some of the side charging AR uppers or use the same concept of a m11/10 charging handle that is installed after the bolt is in place.

Not only "NO" but "NFWIH NO".

Unless you have some mystery element up your sleeve that's about 2 or 3 (maybe more) times the density of depleted uranium, there is no way you're getting enough mass in a half-length AR size bolt to work as a 9mm blowback.  There is a reason things are made the way they are.

You want a folding stock that bad, you need some kind of locked breech mechanism (example:  MP5, MPX) or a larger cross section to the receiver so that sufficient bolt mass can be achieved in a shorter space (example: HK UMP/USC).

This is a most interesting thread with some very bright and inventive people like the famous "Mad-Machinist", people who really put some serious brain power into this stuff. As I follow this however I do wonder why people limit their thinking.that these things have to be built into an AR platform. The AR platform is OLD. It was also built to be a gas operated firearm. The impinged system has its limitations as all should be well aware of. In every competition the military has done the M-4 sort of comes in last place.  As for 9mm you have a system that is even weaker. If I recall the whole 9mm thing was started as a way to make a simple conversion of an impinged 5.56 into a PCC.  That worked, but again with limitations.

I think its a credit to a large group of very intelligent people that we have seen so many variations built on the basic AR platform. Personally I have AR's in four different calibers and enjoy them all. But, as time has passed and I have lived with these calibers I can no longer dismiss the clear limitations of the platform, especially with the 9mm blow back guns. 9mm blowback firearms have their limits. They run dirty. They need a bolt with a lot of mass to contain them. I have six or so blowback 9mm carbines/rifles and each has some compromise to get it to function well. Mostly its the very heavy bolts.

Look at the construction of a Marllin Camp 9 or a Beretta Storm 9mm. They are built in such a way that they could have a folding stock. The AR design however has the bolt running too far back into the receiver and needs that buffer tube for it. Now, if you want a folding stock you have to go to great lengths to make major design changes as you try to keep the general outward appearance of the firearm. To be quite honest, why bother? It would seem easier to look at some other platform or even start from scratch to build a shorter action gun that could have a folding stock.

In the end however I just pull out my CX-4 Beretta and think, "Why go to so much trouble?". Short, compact, reliable firearm. No stamps, no hundreds of hours of work, nothing.  Stick a magazine in it and go shoot. On the other hand, if you just love working, working and working on your own design, some thing truly unique, then go for it! I got too old and burned out on AR's to spend that much effort on trying to make it into something Eugene Stoner did over fifty years ago with a different direction in mind.

Never underestimate the power of building on an AR lower receiver - $40 "firearm" and the rest "parts" - plus easy 80% receivers for folks who wish that route.

I love my Camp9 - and have for the last 20-odd years, but there never were very many stock choices for it - scope rail is interesting, and you can have any iron sights you like as long as they're the factory ones  I never found a 20-30rd magazine which worked for it.  (Remember "USA-brand" magazines? Shudder!)

There are factory 20rds for the CX4 at least - and if I ran a 92 or PX4, I'd have one for sure

For us poor slobs in ban states, magazine compatibility becomes a BIG deal - the MPX using proprietary new magazines makes me cry.  I've got a big stack of Colt/Uzi-style magazines, a handful of MP5-type magazines, etc, so for me, being able to use those is a big big deal.

YMMV, and all that

It's a interesting idea, but I would imagine there would be very little demand with the new PCC's that have been recently released.

This is something I would buy.

This is what I am thinking so far in custom parts

Cut down 9mm bolt
free float rail system/guide for relocated mass from the bolt
2 x Guide rods modded from a M10 parts
2 x Springs from M10 parts

What I need to do is figure out how much mass I will be removing from the bolt
How I want to rebuild that mass into a hand guard.
How I will attach the bolt to the relocated mass.
How I will make this easy to assemble and disassemble for testing/end user cleaning and lube

After that, I need to look at loose enough tolerances to move freely but not loose enough that I would break the connecting rod.
Also thinking about the back end I need to think about a cap and maybe reinforcement to the rear/buffer tube hole

I wonder how much stuff I will destroy while trying to make this work.
I'm betting a lot of connecting rods and one upper will be FUBAR by the end

How about a tungsten bolt carrier for additional weight?

In an end product maybe but for testing I have to use as many parts as possible that are already available.

Build it to work first, then build it pretty and custom

If I can do this with common parts then conversion kits will easily be made

Same point in using an AR lower, common parts.
Then there are mags, glock and colt depending on the bolt a little.  Again common parts.

If all you need is a bolt, connecting rod, and hand guard system then conversion would be easy.

If your objective is to manufacture an AR15 style PCC with a folding stock would it not be better and possibly cheaper to just design a gas operated locking breech retrofit? You could use the same the M10/M11 recoil guide rods and springs along with a chopped standard carrier. The only difficult part would be spec'ing a piston system to work with the lower pressure gas from the 9mm cartridge and tucking it up under the handguard. You would also have to figure out how to solve carrier tilt, but if Sig pulled it off with the MPX then it shouldn't be too hard to make the same concept work on the AR15.  In my mind locking breech gas-op > blowback, but that's just my opinion. Either way you go it sounds like a fun project and I wish you best of luck.

the MPX has the gas port right at the leading edge of the chamber, and the piston is tucked up tighly to the barrel, it would be difficult, but not impossible, to replicate this in an AR-pattern upper, but "off the shelf" components kinda goes out the window.

I've built some DI.45s, and i experimented with a piston, but couldn't get it far enough back without completely butchering the upper and making it difficult to disassemble and service.
If 9mm weren't so dirty, DI would be the way to go.

.45 on the right

Damn, that one on the right looks sweet

Much as it pains me to say this - the MPX appears NOT to have solved the dirty issue.  From all reports it keeps RUNNING, so by some folks' definition that IS solved, but not mine....
http://www.ar15.com/forums/t_6_45/445783_MPX_running_dirty____.html

I don't care how dirty it is unless it stars to cause too much friction in the action and affects function. Anything that's semi-auto and shoots factory pistol ammo is going to be dirty.  How much that crud affects function is another matter.  The MPX uses a vented piston to keep some of the crud out of the bolt/carrier, I wonder how many rounds it can take between cleanings before binding up.

I'd say you have some unreal expectations if you expect any PCC to stay clean when you shoot it...

They're real expectations all right - perhaps unreasonable

Ok, so WHY is it an unreasonable expectation that an 8" 9mm piston gun should run clean when a 7.5" .223 piston gun *DOES* run "clean"?  (Both on factory ammo)

Formerly I attributed the unreasonable expectation to the fact that PCCs ran blowback - and it's demonstrably dirty in pistols as well as rifles, so no shock there.  


Locked breech 9mm 3-5" pistols run clean, so I'm again not sure why this is an unreasonable expectation from a rifle?

I'm willing to be educated....

Powders used, bolt unlock time and barrel length, mostly powder type.
With a pistol,  all powder and filler is out of the bore before the slide unlocks and the case begins extraction.
In the case of blowback,  the case begins extraction immediately.
With gas guns and piston guns,  the gas and powder that are vented end up somewhere, on top of what exits the breech.
I'm not sure what ammo you're using that runs 'clean' in a handgun but 'dirty' in the MPX, but put 100rds through both after cleaning and compare, handguns are dirty.

Agreed - so do you think an 8" locked breech pistol would start being dirtier?  I guess I never directly compared a 3.5" to a 5" for instance, but I don't think my little PM9 runs noticeably dirtier than my P89 or 5906 - though neither of those have "long" barrels.



Agreed - but in the .223 that somewhere doesn't get terribly dirty.  The piston and vent area are of course not clean, but the chamber and receiver area are.  I think the unlock time is the most likely culprit from your description - the MPX is opening "early" compared to the .223/.308 guns.  My question then would be "Must it?"



UMC Green Box - and I did, the same day I did the MPX vs AR9, I ran close to 100rds through a 5906.  There was very little powder fouling in the 5906, just a few swipes to get the slide and frame clean and a couple on the feed ramp.  Maybe half-dozen patches to clean the chamber and bore.  My experience is that BLOWBACK handguns are dirty, but locked-breech are "relatively" clean - the point I was making is the MPX is EVEN DIRTIER than blowback.  (Again, I don't dispute that it might keep running longer - I just didn't test that, and am not likely to burn up enough 9mm to prove it on my own dime!)

One thing I don't like is how long the ar receivers are. I bought a DDLES lower as well as a mp5k upper and like the smaller size of the HK but even it is longer than it needs to be.

I had never heard of the gilboa till this thread but looking at pictures it sure seems like a good size. I always liked the TP9 too but it's proprietary barrel made suppression tough.

And so it begins

The m10 guide rod almost fits perfectly.  I need to look at length and a few more ideas

You have to replace not only the mass of the back half of the bolt (bolt plus tungsten weight) but also the weight of the 9mm "buffer" as well.

I was thinking about that as well.  

Lots of things to look at:
Force generated from a 9mm being firedwith the modified bolt
the mass of buffer and any mass removed from the bolt
resistance force of the buffer spring
mass of new connecting rod
mass of relocated forward mass, with ability to fine tune the weight
resistance of M10 springs cut to length to fit and work with length of travel that will be needed
the use of guide rods or track type system inside the rails
the ability to separate the bolt from guide rod, or guide rod from relocated mass
buffer tube hole filling/reinforcement possibly with a spring in case of over travel by the bolt
charging handle keep it, remove it, or side charge it?

First build on my pistol lower to see what can be done, 2nd build on a nice lower to SBR it

Where is everyone getting the caps they are using in their bufferless AR22 builds?  
What folding stocks are out there?  I would like to find a slim design similar to the gilboa stock.  

http://www.agparms.com/agp-arms-ar-15-folding-stock/

One option in folding stocks.

Spring can be contained in the upper receiver, or can be forward of the upper under the handguards, acting on the operating rod/action mass.  If there's no fixed sight block, oprod can unscrew out of the front of the free-floated handguards.

I have seen that.  I want to seen one in person before I buy it.  if its all plastic then I'm not so sure about it, but might be worth a try.  I was also thinking about the Romanian AK side folder as a base for a possible concept.  



While reading your post and thinking also about the charging handle issue I decided to check the M10 rod's fit on the charging handle.  

It fits fine

Now do I want to thread or pin or e-clip attach it to the "gas"/op rod key

To some degree the force of the hammer hitting the firing pin and the hammer spring also help keep the bolt closed.

As an engineer I feel I should point this out.

Spring rate has VERY little effect on initial bolt speed.  The mass, and therefore inertia, is the primary controller of opening speed once the impulse is imparted.
After that, the spring rate controls the bolt deceleration, how fast the bolt is still traveling when it reaches it's rearward limit and how fast the bolt closes.

If I wasn't at work I would drop some example equations on you.

My experience is only anecdotal in terms of 1911/2011 raceguns built for USPSA competition.



You'll have a "rib cage'd", lightened slide, with maybe as low as a 9 pound recoil spring, and maybe a 20 something pound main spring (for the hammer).  Some guys can say they can feel the difference in the recoil impulse between a rounded firing pin stop vs. A squared off firing pin stop.  

And yes, I do realize there are locking lugs  and barrel links involved.

Here is the bolt/BCG from a Para TTR (Zitta):



I have no idea what this:



It does not look very elegant.

It just popped up in a google image search for "Para TTR bolt".  

There is also a video of Todd Jarret disassembling a Zitta "TTR"

The bottom one is an Oly OA93/96 pistol, and I've actually had a ZM LR-300 carrier assembly in hand.  The gun in my avatar is based on a beefed up version of the ZM gas system.

With an AR, the speed of the bolt can be entirely controlled by how much gas you feed it and for how long, all that remains is sufficient spring force for feeding from a mag and to overcome any drag from things like dirt, and then enough carrier mass to drive that spring back far enough upon firing.  It's all a balancing act.

With the 1911, the rotational inertia of the hammer relative to the firing pin stop contact point can certainly affect slide speed when you're using a super light slide.

I'd say I know a thing or two about bastardized ARs

ZM top, mine bottom




Carrier from the .45 above:

This thread? http://www.weaponsguild.com/forum/index.php?topic=53142.0

The crucial difference is that the other examples you offer are locked breech firearms.

In a straight blowback, the inertia of the reciprocating mass IS the locking mechanism. Springs have a minimal effect on the "unlocking" speed of a blowback.

Which is why I suggested a locked breech approach to begin with.

I was out looking at recoil formulas online. I am planning on doing the math and seeing how it computes to the theory in my head.

I am fascinated with my idea and making it work and work right.
The second half after i get it working will be interesting too.

ETA some of what I have been reading up on. https://en.wikipedia.org/wiki/Recoil

The Rock River PDS carries a good bit of weight in the piston rod assembly. Even a blowback should be able to spread the weight over a larger area. But then, I ain't no RDTCU by any stretch of the imagination.

I don't think the world could handle more than one