I think you mean PCC.....sub gun means full auto....if you tried a full auto MP5 or anything not blowback to something that is straight blowback in full auto it would be clear that straight blowack will never be as smooth.

Maybe not important to a lot of people here.  How many people buy these PCCs for plinking vs training vs competition.  If you're just plinking you probably dont care about dot bounce, split times etc...but my point is for $350 retail you can get delayed blowback with the best ergonomics and modularity...so why not?

Full auto MP5 is buttery smooth.

Yes it is....and so is my CMMG Guard now...but also is:
Ambidextrous
BHO
Modular
Better cyclic rate
Better trigger (Geissele SSF)
So retiring my full auto MP5

That's the funny thing about it. There is absolutely a technical aspect here. And there is also a practical physical amount of measurable force on your body. On one hand I don't like JP GMR 9mm carbine because I think it's a rip off, suppresses like every other straight blowback 9mm AR and it has a lot of recoil for what it is - but - the dot does come back on target and split times can be fast. It's something you need to experience over direct comparison back and forth testing.

But once you know it, you're ruined.

My hope is to ruin more people so mfgs start making the delayed action guns that I want. :)

Oh, I don’t doubt any of that. That’s why I’m going to build one that uses MP5/40 mags.  I’m trying to decide on the 5” or 8” barrel, but I’m leaning towards the 8” at the moment.

You want to do a 40SW Guard?  I need to shoot mine some more but think its kinda rough.
Again, as mentioned on threads here and my blog site, I didn't like the 9mm Guard with the recommended buffer/spring setup.  They cut the angles on the 9mm to work in a large operating window.
So much so that as seen on the previous page the less aggressive 40SW bolt works in 9mm.....(suppressed ony)

So likewise, I think they cut the angles on the 40SW to be too aggressive for 40SW to give a large operating window for 40SW......EX....If/when they releas a 10mm Guard that bolt will most likely result in a smoother 40SW.

Not want to.  Going to.  NFA C-5 lower is at the LGS waiting for me to pick it up and MP5/40 mag shipped today from HKParts.  I'll start there with the fitting of the mag in the lower, then decide if I want to take apart my straight pull .300blk upper and use the Lantac side charger or buy a Bear Creek or Gibbz upper then fit the mag to that.  Then it'll be time to buy the BCG, barrel, buffer, tube, and spring and dick around with that and the feed ramps on the lower.  At some point in there I'll need to file a Form 1 for another can.

I have your site bookmarked for reference.

Nyet. Delay blowback is fine. Actually, it's cheap and simple, not optimal. Any PCC advertising a price above $400- which is a lot of them -utilizing a  straight blowback design is ripping you off. Which is why I won't go any higher than a HiPoint or Keltec. Even the new ruger is pushing it for me. I took a sub2000 as a balance of pros and cons, blowback being one of those cons. One day I'll probably even buy a hiPoint in 45acp becuase... Well, anything else in 45acp is stupidly expensive. But again, it's blowback and cheap, not a PCC masquerading as a Tier 0 operator gun costing a nearly a $1000 that still uses blowback.

Not sure if serious, or just believes guns should be zero-margin items for manufacturers...

NFA C-5 lower?...isn't that for 9mm MP5 mags only?  MP5 40/10mm mags engage a catch on the back....not the side like a 9mm MP5 mag....or is there a C-5 lower out that takes MP5 40/10 mags now?

Same lower.  Have dremel, will travel.  I think a sanding drum will do the trick since the mag body is plastic.

Wow...good luck

Its really no different than cutting mag release notches in Uzi mags to use in Colt-style lowers.

Yeah..but Uzi mags are steel.  You are talking about notching polymer mags as well as probably having to enlarge the magwell.

Whoops, meant straight blowback. "Delayed" snuck in there somehow.

But a keltec makes it painfully obviouus-- it's two pipes and a big spring. Nobody should be paying more than $400 for that but slap an AR chassis on it or give it a brand name, presto. Kind of like how making a rifle a bullpup magically adds $200 to $400 to what would otherwise be a mediocre rifle.

I had a good laugh when I read this, this needs to be a shirt or a sticker.

This thread has been very good.

Well, I possibly can fit the mags to the magwell similar to fitting AK mags.  I should have the first batch of parts Monday so I can see just make I'm working with.

I've wasted more money on dumber things, but I like a challenge and enjoy tinkering on stuff like this.

+1.  I like your style.  Looking forward to the pics!

They sure don't teach economics like they used to, no wonder socialism en vogue today...

When you have to make everything in-house (ie not Palmetto), and you aren't making it in massive quantities that are guaranteed to sell (ie not Ruger), and you are having to actually machine most of the parts in some way (ie not Hi Point), production costs will be higher.  For all the talk about how cheaply KTs are made, the designs are rather inefficient in terms of parts count --which adds to the cost (and I think contributes to the QC issues), but allows KT to avoid paying for specialized machines.  The result is a more dynamic business model than, say, Hi Point, but with costs that are slightly higher than they could be if Kelgren had decided years ago to optimize the whole production line around, say, P3ATs.

The barrel itself is the bulk of the cost of any gun design, especially blowbacks.  To be honest, the delay feature isn't all that much additional cost, but it is a significant differentiation from straight blowbacks, and one people are willing to pay money for.  I suspect if we more than a couple more sophisticated designs out there, it will eventually drive costs of simple blowbacks downward (stuff like the Scorpion won't cost the better part of 1000$ for example).  Except B&T and H&K, because they are expensive largely for the sake of being expensive (I bet B&Ts margins are a lot lower than H&Ks, though)

Needs to be on a business card

I don't know. If we are talking about full auto specifically, there is certainly a benefit to slower cycle speed. Slower cycle speed has no real benefit in a pistol caliber semi auto.
For a semi auto, straight blow back is a simple and reliable design. Why complicate things when there is no benefit? Adding a locking bolt or a delayed blow back is adding to the parts and complexity when it isn't necessary. There are plenty of reliable straight blow backs to prove it's ability.
I realize the semi auto guns we use are often neutered from a full auto design, fair enough.  Building two versions of the same gun to satisfy the full auto version and semi auto version is how things are done, 'they are different'. I'm sure most people want their semi as close functionally to the full auto version as possible but that requires reverse engineering the function based on what's best in full auto. Full and semi are different whether we like it or not. Again, why complicate a semi auto design with features that only benefit the gun in full auto?

For what it is worth and not to get too far off optic, when I was in high school not so long ago we didn't do a deep dive into economics. We briefly looked at how the economy affects us everyday, and how the different types of economies that a government chooses to participate in affects that governments and nations growth.

It wasn't until this last fall and spring semester that I actually took macro and micro economics. Before that I had a hands on understanding of manufacturing economics.

There's a lot more benefit than simple rate of fire, which has more to do with bolt travel than anything

What benefits are there to delaying the bolt unlocking in a semi auto 'pistol' round? At least, what benefits are there in delaying the bolt from moving from battery slower than a weighted and spring loaded blowback bolt carrier can provide?

I would argue that you are further complicating things going to a straight blowback 9mm AR vs a delayed blowback CMMG.
Pictured below are the only two unique parts you need to do a delayed blowback 9mm AR from CMMG:


Now, for straight blowback you also need a 9mm barrel and bolt right?...so it is a wash there...
But what else do you also need for a straight blowback 9mm AR?
1.  Excessively heavy buffer for more reciprocating mass.
2.  The buffer also needs to be longer OR use a spacer to restrict how far the bolt travels so you don't snap off your bolt hold open from all that excessive mass flying forward when the BHO is engaged after firing the last round.  Again because the straight blowback 9mm uses a solid bolt and again has a different geometry than a 556 BCG....while the CMMG has a proprietary bolt and carrier, the distance the bolt protrudes from the carrier is the same as a 556 and the bottom of the carrier is identical to a 556, while you have a hodge podge of different ramped bolt angles for the 9mm straight blowbacks out there.
3.  Considerably stronger spring to help soak up the recoil.
4.  Several trigger manufacturers also do not the support the use of their triggers in straight blowback 9mm's due to the recoil.  See following thread where Geissele chimes in: https://www.ar15.com/forums/Armory/m16-w-geissele-SSF-trigger-and-a-colt-9mm-upper/23-492959/?page=1
Now Geissele didn't comment back on the Guard specifically and they may not care to as it is hard for a manufacturer to test their products with everything out there.  I run my Geissele SSF with my delayed blowback Guard and see no issues as it is softer shooting than my 556.

With my Guard setups, I am literally doing just an upper swap.  I make zero changes in the lower.  Can anyone say the same for a 9mm straight blowback?  Even with Endomags, if you did that with straight blowback, you would most likely be running too light of a buffer and spring in your 556 for it to run 9mm without encountering trigger slap and a rough shooting upper.

How many times do we see threads about trigger slap with a 9mm straight blowback?  It is a very common problem.  This simply doesn't happen with the CMMG delayed blowback.

All these straight blowback AR's all have to elevate the mag higher for feeding.  The Guard is actually bringing it back down to the same height as 5.56 due its similar bolt and carrier relationship.

While most of my testing is about full auto, if you look at my site, one of my goals is also suppression, the delayed blowback suppresses way better than any straight blowback.  It is stupid quiet.  Like my MP5.

Again, going back to my analogy of a Hipoint 9mm pistol vs Glock or any other non-blowback pistol, the benefits are obvious and very few manufacturers do straight blowback 9mm handguns as it is quite clear what the benefits are when shot side by side.  I think the benefits are less obvious when we are talking about a shoulder fired 9mm.

However, it is evident even for a semi auto, it can be seen in rapid shooting paying attention to your split times and dot bounce.  Many people just looking for the plinker may not care or notice the difference, great see your point but my point is if you look at all the points I made above about compatibility with your 556 lower why wouldn't you want to go delayed when you are actually making things less complicated and MORE compatible.

Lastly, price....I think everyone reading this already has an AR15.  So you can just get the BCG/BBL combo starting at $350 retail and slap it together at a low cost.  Most people here have Pmags.  So you can get Endomags and if you want to go cheap just swap guts till you want to buy dedicated Pmags for the Endomags.

Sure you can get a straight blowback bolt and barrel cheaper than $350, but don't forget my other points, you will now need a heavier buffer, spring and if you have a nice trigger like a Geissele the mfr may not support using it in a straight blowback 9mm setup.  So are you really saving anything and making things less complicated?

I'm sure the CMMG is a fine and reliable weapon. The use of an AR trigger is nice since ARs have nice reliable triggers.
As far as the complexity and parts goes, it's still more complicated (more going on and requires added parts) than a simple blow back. In a Blow back weapon, you have the carrier/bolt and a action spring to cycle the action, that's all. In the CMMG, you also have the same carrier/bolt and action spring but you're adding the complexity of separate carrier and bolt and the bolt rotates unlocking from a lugged barrel extension. I would assume the rotating bolt can be sensitive to pressure changes? A blow back, blows back and that's it.
Adding more complexity may very well make for a smoother or softer shooting weapon? More complexity isn't a bad thing as long as everything works reliably.
My point is simple, blow back works and is reliable without added complexity. I guess I consider non blow back semi auto as unnecessary over engineering.

Agreed..and to my reiterate on my analogy...that is why we rarely see straight blowback handguns anymore like Hi-Points.  Browning lockup as well as other mechanisms over straight blowback have been proven for over a century now....
I do not think it is over engineering...rather I think it is way overdue...it is 2019 and straight blowback handguns are pretty much a rarity these days while it is the opposite for PCC's.

If we are talking semi, I would rather go with a modified Browning lockup Glock in a Roni chassis than a straight blowback AR.

My petite wife and kids can handle my 9mm CMMG Guard even in full auto.  I cannot say the same for a straight blowback 9mm.  One round and they are handing it back.

Again, suppression is also superior with no port 'pop' like you get on a straight blowback 9mm.

Wow, the rof on the guard was really impressive.

You own a handgun, right?  Is it a Glock/etc, or a Hi Point?

Less moving mass, less recoil, less spring tension.  Big benefits, even in a semiauto.

Don't you also need an enlarged ejection port for the upper on the Guard? Or is it just the 45?
Thanks

Only for .45

CMMG sells the enlarged uppers for 9mm too. But I don't think it's needed. 9mm is the same size as 556, but I think the concern is they come out a little crooked.

I used an Aero XL, worked great.

I dont know,

Theoretically you are correct that straight block is not as smooth delayed roller action, but being 100 percent unacceptable is a little silly.  i

I could see if your sole criteria for selecting a weapon was recoil impulse, but if in order to achieve that goal, you have to go to a weapon system the is more susceptible to fouling/sensitive to ammo with horrible ergos, slow mag changes, no last round bolt hold open/bolt release and garbage trigger that most likely was built in in some 3rd world shithole.

If JP can achieve 95 percent of the Mp5's smoothness and nail all the other factors being a blow back action, That IMO is totally acceptable. at least is actually produced by Americans. same thing applies to the B&T GHM9

If anything, choosing a PCC/Even a Delayed Blowback over a 300BLK/PDW should be considered unacceptable.

I will eventually pick up a Mp5 Variant but for as awesome as it is, its just going to be a toy since at the end of the day, its still a 9mm. In the even that something needs to be grabbed to slot floppies, its going to fire a rifle round

95% huh?

If it's good, I don't care where it's made.

Are pistols toys?

Is it good? Shit ergos, slow reloads, shit trigger, heavy for the size of it.

Are pistols toys? sometimes.

What would be the primary reason to chose say a 6lb Mp5K variant over a sub 5lb Honey  Badger. The HB outclasses the Mp5K across the board.

The Mp5 does some stuff very well but struggles in other areas.  It's a PCC that belongs in the collection of most shooters.

Yeah it's good. Have you even tried one?

The MP5K weighs 4.4 pounds and can be concealed under a coat in a shoulder harness.
That'd be a primary reason to choose it over the Honey Badger.
Mission dictates equipment.

Surprisly, no, it's one of the few classics that I have not shot. I plan on picking on up. While I will concede its recoil  is best in class, reloads are twice as long, and have limited range.

Once again, why would one run a 4.4 lb mp5k when you can run a 5 lb honey badge with a folder, have have three times the range, subsonic capability, modern ergos, trigger and faster reloads.

The Mp5k is the king of obsolete weapon platform.

That doesnt mean that it cant be an effective tool, and quite fun to shoot. But just like an AR PDW outclasses an mp5, the mp5 edges blowback guns. It doesnt mean blow back guns cant be effective on target.

Fuck, give me 4 hobos, some mosin M38's and some MD 20/20 and they could probably overthrow NZ.

Is there a list of glock lowers that work with the CMMG upper?

This is more in response to your comments on PCC not particularly to the MP5 comparison....
1.  Shoot steel close up.
2.  Cheap to shoot.  I reload jacketed 9mm 147 Gr for about 11 cents per round
3.  Good for training, same lower as 556/300 BLK and again, so can shoot more since cheaper to shoot and also allows use in more ranges since it is pistol caliber.

Pictured below is my Radially Delayed blowback CMMG Guard.
Has all the modern Ergos, Geissele SSF trigger, fast reloads, BHO on the mags, with the PDQ, I can lock the bolt back and release it on the right side.
Using the Endomags, so same mag pouches as 556/300 BLK.

I want to shoot 556/300 BLK, no problem.  Literally just an upper swap.  Everything in lower stays the same.

Yea, IF JP blowback guns could achieve to be 95% as smooth as an MP5 that would be something! That is wholly not the case though :(

This is the point of this thread - if you think blowback and delayed are "about" the same thing - you don't actually know the difference.

And that's fine. But, there is a difference whether you understand it or not, and to go from delayed back to straight, is actually pretty unacceptable (with scenarios cut out for open bolt auto and some other atypical uses). If you are happy with your straight blowback guns, don't go looking, it can't be unfelt.

Sorry man, but JP guns don't get anywhere near 95% of an MP5. A JP GMR 9mm has more recoil than a DI 556, that sucks.

Great thread.  My 5" Guard and endomags should be arriving today.

Main goals were suppression and for a good trainer platform for my kids.

Looks like a 40 bolt is in my future when CMMG makes them available.

Now to decide whether to wait the year on a Form 4 for a TiRant 9M or build a Form 1 can to lessen the wait time.

Probably should Form 1 a lower for an SBR as the pistol brace is kinda meh.

“CMMG Guard” better than MP5, BT etc??   LOL

The fact that the Guard requires a huge buffer tube sticking out of the back of a 9mm is an automatic fail and a sign that you are 50 years behind engineering in your "new" design.

Try again OP.  Get back to me when the radial-delay blowback is paired with a compact recoil design such as that used in the SIG modified AR weapons.  There is absolutely no excuse for designing a modern 9mm weapon with a foot-long+ recoil assembly.  Ridiculous.

(and yes, I do in fact own 2 AR-pattern 9mm, but am not delusional about them or the design hack that the AR pattern buffer tube mandates)

You mean like the ability to drop it onto an existing SBR or machine gun lower/RDIAS?

Or drop it onto an existing 5.56 lower for lower cost training with an identical manual of arms?

Not sure why Amphibian, who clearly owns most of the platforms discussed in this thread, would have any impetus to state anything other than an opinion unbiased by confirmation bias.

I guess if concealment is priority 1, a folding stock would be nice.   I think you could get that feature with the LAW folder if you were so inclined.

Its not necessary if you're willing to chop the carrier and make a custom recoil assembly.  I guess you failed to realize that the Guard was designed to be plus and play with existing AR setups.

I guess you failed to realize OP brought up CMMG “as delivered” as a superior solution to MP5, BT, etc.

And yeah, once you get into a custom built action, anything is possible, but I thought we were talking about commercially-available weapons, not one-off customs.

"CMMG Guard is the best 9MM PCC/PDW action within the confines of the standard AR plartform"
is an entirely different argument than
"CMMG Guard is the best 9MM PCC/PDW action of all weapons platforms available".

I might agree with the former, but have a significantly different opinion on the latter.

I plan to do just that at some point, and compare it to my bufferless DI 45 setup.

Attached File


The angle on the lugs will be critical due to the reduced carrier mass, may look at using a .40 bolt with 9mm, as Amphibian is doing with his super-short barrel suppressed RDB upper.

+1....exactly.
Better than the MP5...yes...look back on page 2 of this thread and I list 10 facts why it is.
Aren't we on AR15.com?  I happen to like the AR/M16 platform.  The ability to do a straight upper swap with 556/9mm with no lower changes is a great plus.  Being delayed blowback another huge plus.  Lastly, using the buffer tube is an advantage to me as well so I can leverage the enormous buffer/tube/spring options out there. (With new innovative variations coming out all the time).  As I've posted many times, I think out of the box, the CMMG is way better than any straight blowback AR but lags a lot behind the MP5 in terms of smoothness....however just changing to the A5 length tube, 556 Tubb flat spring and hydraulic buffer it is now very close to the MP5 and already smoother than a straight blowback BT (not including TP9 which is a Steyr design)

As I posted before, I have a full auto Sig MPX and don't like it at all.  Smaller operating window even with the ILWT 4 position gas regulator.  Not tunable.  Stuck with the recoil system from Sig.  Suppression sux...gassy and too much gas leakage of piston making it loud.

Not trying to be a CMMG fan boy but I personally believe it to be the best 9mm closed bolt option today.  If someome comes out with something better I'll certainly welcome it.  I've said many times I'd like to see a roller delayed 9mm AR upper but again, I DO want to use the buffer tube to take advantage of all the options out there....as another example see that Taccom just released a new delayed buffer system using magnets.  While currently only designed for short stroke pistol caliber ARs, sounds like they will release a long stroke version....I would be interested in trying that.  I like options...

Got a chance to put some rounds through my new 9mm upper yesterday.

Swapped it straight onto my 5.56 AR pistol lower with an H3 buffer.  Ran mostly well, 100 rounds with one failure to extract that resulted in a stovepipe type malfunction.

Pulled my standard weight JP SCS from a different AR and tried that.  Another 150 rounds with one more malfunction that occurred when my neighbor was shooting and he cleared it before I could see exactly what happened.

This was all with WWB ammo.  The standard weight JP SCS felt smoother.  When I get a chance this weekend I am going to try a standard carbine buffer, as well as the other two, and run some drills to see if I can discern which is faster.

I was really impressed with the accuracy.  I was mostly shooting steel and I was stacking hits one on top of the other on freshly painted steel.

LRBHO worked perfectly every time.  Overall I am very impressed.

Couldn't have said it any better myself. No AR9 platforms of ANY design are going to make me want to give up my HK's and my B&T's.

Too bad the CMT AR-Mini is still vaporware.
I never heard whether it was delayed blowback or any other details really.



I'm also curious if the Strike MP5 uppers are dead...