Radial Delayed Blowback

[Sgt_Mike1]

figured I would ask here as some Have actually dealt with this system specifically to the 9mm only and I have not any experience. most of my experience is with the traditional blowback as used by Colt.

So my question here is I understand that the Locking lugs of the bolt is chamfered beveled. The barrel Extension I'm wondering if is standard 5.56 type or if propriety ie shortened in the distance between locking lug distance of the extension and barrel. OR is it done to the same dimension as the 5.56. I'm assuming that the feed ramp of the extension is not the same as the 5.56mm/.300 black.

 

[Demi-human]

I’m adding just to follow along.

The feed ramp is not the same, as a 9mm would get hung up on the narrow rifle feedway.

I’ve just been reading on this now, as I’d like a 45 Auto PPC, ala’ modern Tommy gun. And RTB.com has the BCG and barrel sets for sale. This link doesn’t really say much about your question, but someone might find it interesting.
https://ultimatereloader.com/2022/03/26/tested-cmmg-radial-delayed-blowback/

Sounds good to me!

 

[243winxb]

No experience. Just googled it.

I would ask here?

https://www.righttobear.com/radial-delayed-blowback-9mm-bcg-and-8-inch-barrel-99d517a/

Now you can build your own CMMG Delayed Blowback SBR rifle or pistol. You can even use a standard AR lower receiver with these PMAG to 9MM Conversion Adapters (see link below)

https://www.righttobear.com/cmmg-mk...conversion-adapter-delayed-blowback-only-2pk/

Patent Pending? Different patent? https://patents.google.com/patent/US20180142972A1/en

 

[Sgt_Mike1]

Demi Thank you for a quick reply. Yes I look at that link before posting as well.

depending on the setup such as endomag versus a Hahn device modified or a Older CMMG MK9 a barrel extension feed ramp maybe a moot point I dont know for sure. my basis for such a statement is the traditional blowback feeding the ramp is fixed to the lower versus the barrel. And I know that CMMG has a refit kit for those of us that have the OLD non RDB MK9 lowers, in that kit a new feedramp for the lower is included. could a Hahn device be modified with the same kit as the refit of a MK9 lower it is possible i think so but not for the faint of heart.

I know that the cam pin path is completely different than a regular AR15 BCG just by photos and is not interchangable.

In responding I re started a google search I found the following graphics that I never seen earlier before posting my question .


found the above graphic on Primary Arms website





based on what I'm seeing from the graphics, One "might" be able to use a regular extension provided that one modifies the feed ramp when doing a cartridge based on a 9mm case (.30 Luger and .22 TCM comes to mind, as cmmg doesn't offer those calibers).

One of the other interesting thing I came across was that a cmmg 5.45 AR bolt could be used with a RDB carrier effectively converting to akin a bolt action. found that on AR15.com.

P.S. Thank you 243winxb as you posted while I was working on this post

 

[Demi-human]

I wonder if the bolt lugs are wider so they start their travel already off of the extension lugs. It doesn’t have to be a flat face for the bolt lug angles to ride it, but it wouldn’t work if the angled part wasn’t past the edge beforehand.
Looking at the picture of the extension from the barrel, there seems to be a rounded or beveled corner to the extension lugs. This could be perfect to initiate the rotation of the bolt.

Thank you for the pics.
I am even more interested now. A 45Auto PPC would bump my 300Blackout out of bed.

 

[halfmoonclip]

Hey Sarge, thanks for the diagram. I've been studying it for 5 minutes, and CANNOT see how the cartridge could impact the bolt carrier (as the gas does with an AR). Instead, the case head must push on the bolt itself; the 'locking lugs' are tapered, not square. So the bolt itself turns, unlocking (with the help of the cam pin?), and then pushes everything to the rear, extracting and ejecting.
The bolt is never truly 'locked' in the sense of an AR, but that radial motion should at least tend to slow things down.
Watching Honest Os review, it does appear the Banshee has more recoil than the MP5. But I had a MPX, and never thought the recoil was much different than a Scorp.
For guys who are gun racing, perhaps it makes a difference; for the rest of us, not so much.
Moon

 

[zaitcev]

The bolt is never truly 'locked' in the sense of an AR, but that radial motion should at least tend to slow things down.

There's no "at least tend" about RDB at all, it's a proper 2-part delayed blowback. Its principle of operation is no different from roller-delayed (H&K) or lever-delayed (Kirali) action. Unlike the 1-part systems, like Reising, the action contains two parts: a bolt and a carrier. The bolt is locked against the receiver in such a way that it can still move, balancing against a mechanical disadvantage and the mass of the carrier. The leverage in the disadvantage, thus, is how much lighter the carrier can be versus a bolt of an equivalent straight blowback gun in the same caliber.

 

[someguy2800]

I had one for a couple years. I am 95% certain it was just a normal 5.56 barrel extension on the barrel unless there was some modification that was not easily visible. It was incredibly soft shooting and it fed very reliably, but I could never make mine eject reliably. Brass wouldn't make it out the port and would stovepipe. I went back and forth with CMMG customer service on it for a long time changing springs and ejector plungers and modifying the receiver and I finally gave up. I hear generally positive reviews from most though.

 

[halfmoonclip]

Zaitcev, maybe I'm missing something.
In an AR, the bolt has square locking lugs; when the bolt carrier is driven backwards by gas pressure, the cam pin is forced to turn in the camway, unlocking the bolt. The action of the carrier is what unlocks the bolt.
With the radial delay, it is the action of the bolt itself that starts things moving; it's rotation is caused by the ramped surfaces on the bolt itself, and the cam track in the carrier.
So in the first case, the bolt carrier unlocks the bolt. In the second, the bolt unlocks itself, and imparts motion to the carrier.
Hence, 'radial delayed blowback' just tending to slow things down.
Moon

 

[Sgt_Mike1]

I had one for a couple years. I am 95% certain it was just a normal 5.56 barrel extension on the barrel unless there was some modification that was not easily visible. It was incredibly soft shooting and it fed very reliably, but I could never make mine eject reliably. Brass wouldn't make it out the port and would stovepipe. I went back and forth with CMMG customer service on it for a long time changing springs and ejector plungers and modifying the receiver and I finally gave up. I hear generally positive reviews from most though.

Sorry to hear about your experience , and without owning one myself I have No clue as to what the cure could have been.

it's a proper 2-part delayed blowback. Its principle of operation is no different from roller-delayed (H&K) or lever-delayed (Kirali) action. Unlike the 1-part systems, like Reising, the action contains two parts: a bolt and a carrier. The bolt is locked against the receiver in such a way that it can still move, balancing against a mechanical disadvantage and the mass of the carrier. The leverage in the disadvantage, thus, is how much lighter the carrier can be versus a bolt of an equivalent straight blowback gun in the same caliber.

Agreed no matter the system roller delay, radial delay, lever delay, or traditional blowback they all are going to the same purpose /destination they are just taking different route or highways to get there. That is to retard the bolt from extracting the case until the case has "relaxed" and can be extracted while there are no forces preventing extraction.

Hey Sarge, thanks for the diagram. I've been studying it for 5 minutes, and CANNOT see how the cartridge could impact the bolt carrier (as the gas does with an AR). Instead, the case head must push on the bolt itself; the 'locking lugs' are tapered, not square. So the bolt itself turns, unlocking (with the help of the cam pin?), and then pushes everything to the rear, extracting and ejecting.
The bolt is never truly 'locked' in the sense of an AR,

Yes in any version of blowback the only impact the cartridge has is via the bolt face. In a gas system it provides assistance onto a carrier which causes the bolt to rotate or move into a unlocked position. I fully understand what you meant in the last part of your post of the bolt not being locked, but in my experience that bolt is in a locked position with the AR15/AR10 family. not to argue a point, but rather clarify as I think you understand the system very well. And really Thank you for sharing your observations, as I'm sure many will find it helpful and you saved me from typing all that.

 

[someguy2800]

Sorry to hear about your experience , and without owning one myself I have No clue as to what the cure could have been.

I took a bunch of slow motion video of it trying to figure it out and its really just a geometry problem with the case being too short. The ejector spring is trying to kick the case out while its still in the barrel extension and the short case doesn't have a large enough moment of inertia to get it heading out the port before its released by the extractor. I think there is good reason why most 9mm firearms used fixed ejectors rather than spring loaded ejectors.

With that said I know other people with CMMG's that run great, so I guess there is a way to make it work. I think it was softer shooting and quieter than my roller delay setup, but the roller delay setup just plain works with every and all loads. From hot +P loads to cast bullets loaded so light they won't even cycle a handgun. It just eats them all.

 

[Crosshair]

Too bad Remington went under, as the Hesitation Lock of the R51 is a far simpler delayed blowback solution. It could have easily been used in a carbine.

 

[Demi-human]

Too bad Remington went under, as the Hesitation Lock of the R51 is a far simpler delayed blowback solution. It could have easily been used in a carbine.

You assume Remington would ever consider the idea. That they are defunct has perhaps gotten the idea closer than ever to becoming used in a carbine…
Besides the Swiss MKMO.

I’ve looked at my other barrel extensions, @Sgt_Mike1, and they all look like the one pictured.
I’d wager the proprietary geometry is in the bolt alone, as that would be the most efficient mode, and that a cartridge conversion that you speak of would work as expected. Provided the new case had enough oomph to make it do so. It sounds like a fun project.

And I am more interested than ever in a Banshee or whatever they call the 45Auto model.
Especially since I can build one cheaper now!

 

[Sgt_Mike1]

I’ve looked at my other barrel extensions, @Sgt_Mike1, and they all look like the one pictured.
I’d wager the proprietary geometry is in the bolt alone, as that would be the most efficient mode, and that a cartridge conversion that you speak of would work as expected. Provided the new case had enough oomph to make it do so. It sounds like a fun project.

Yes I suspect you are correct on the bolt and extension.

 

[Slamfire]

Thompson called his mechanism a hesitation lock.It was supposed to be a delayed blowback, don't know if the Blish principle actually worked in practice.



That brass locking piece slides up and down, and that incline provides the dwell so the bolt does not open at pressures that will rupture the case sidewall.














I have handled a Thompson, never fired one. A Thompson is very heavy, and even though it was so heavy, I was told it would string. No doubt the heavy bolt moved the whole weapon each shot.

CMMG is claiming a light bolt, for less firearm movement during cycling. It sure looks like a AR15 type weapon, so the flippers, levers, mode of operation will be similar for an AR15 owner. And that is all to the good. It is a new weapon design, no idea how it holds up, or how sensitive it is to ammunition.

 

[halfmoonclip]

Sarge, agree, the AR bolts are actually locked at the moment of firing, as surely as a bolt action. The others are delayed blowback.
Slamfire, I remember there being a lot of discussion if the Blish lock actually did anything, or if it just added mass to the bolt. The later, M1/M1A1 version answered that question; it went to a pure blowback.
Had the pleasure of shooting an earlier, (1928?)civilian version. They are cool as hell; very deliberate rate of fire, beautifully made, not especially ergonomic, heavy.
Moon

 

[zaitcev]

So in the first case, the bolt carrier unlocks the bolt. In the second, the bolt unlocks itself, and imparts motion to the carrier.
Hence, 'radial delayed blowback' just tending to slow things down.

The word "tend" means that it does so sometimes. But in this case the action always delays the opening.

 

[zaitcev]

Thompson called his mechanism a hesitation lock.

It's quite unfortunate, too, because hesitation locking as well-defined type of action, somewhat in between a blowback and a locked breech. Its operation requires the case to move, like in a blowback. However, the motion of the case is limited mechanically, and not by the mass of the moving parts of the action. In a typical hesitation locking action, the bolt and carrier are linked by a lug, so that the carrier drives the bolt into battery, and conversely bolt imparts force on the carrier. However, bolt only moves a short distance and lands on a locking shoulder of the receiver. At that point, the action turns into a fully locked one, the carrier continues on its own for a dwell distance and further to unlock and retract the bolt.

 

[Nuclear]

I have a CMMG RDB in 45ACP, and after downloading the extended aftermarket Glock mags by one, plus tuning it with the bolt weight kit for the suppressor I put on it, it now runs well with 230, 200 and 185 grain rounds. The recoil is quite reasonable, less than a 9mm pure blowback.

 

[someguy2800]

Thompson called his mechanism a hesitation lock.It was supposed to be a delayed blowback, don't know if the Blish principle actually worked in practice.

View attachment 1141248

That brass locking piece slides up and down, and that incline provides the dwell so the bolt does not open at pressures that will rupture the case sidewall.

View attachment 1141249

View attachment 1141250


View attachment 1141251

View attachment 1141252





I have handled a Thompson, never fired one. A Thompson is very heavy, and even though it was so heavy, I was told it would string. No doubt the heavy bolt moved the whole weapon each shot.

CMMG is claiming a light bolt, for less firearm movement during cycling. It sure looks like a AR15 type weapon, so the flippers, levers, mode of operation will be similar for an AR15 owner. And that is all to the good. It is a new weapon design, no idea how it holds up, or how sensitive it is to ammunition.

I believe it was the British that figured out the Blish lock didn’t do anything because when it broke you could just throw the parts away and the gun still worked perfectly fine. From like 1942 on they did away with it and the thompson was just a straight blowback.

Interestingly Thompson actually made a delayed blowback 30/06 rifle to compete for the army service rifle contract. If you study how it works it’s using the exact same delay mechanism that the CMMG radial delayed system does, but with a lot more mechanical advantage. It was basically using the bolt handle as the only locking lug. Thank god it didn’t go anywhere.

 

[zaitcev]

If you study how it works it’s using the exact same delay mechanism that the CMMG radial delayed system does, but with a lot more mechanical advantage.

CMMG RDB and Thompson Autorifle are nothing alike actually. The Autorifle is an example of 1-piece delayed blowback mechanism, and I was tempted to include it above alongside Reising. The CMMG RDB action is a 2-piece, like MP-5 or FAMAS. The key difference is that the acceleration in a 1-piece system applies to the whole mass. Therefore, the low acceleration required for a short travel of the case requires a great disadvantage. But in a 2-piece system, the whole point is that the blowback mass moves faster than the bolt, and it can cover a greater distance under acceleration than what is permissible for the bolt. This is they key element present in RDB and that Autorifle lacks.

 

[Sgt_Mike1]

slight thread drift here and at first I really didn't understand that nuclear was trying to say

..... downloading the extended aftermarket Glock mags by one, plus tuning it with the bolt weight kit for the suppressor I put on it, it now runs well with 230, 200 and 185 grain rounds. ......

Then it dawned on me he was using a computer term in a gun applications. Then it became clear his "downloading" was 1 less than the max qty of a magazine ie 25 rds mag load 24, 32 rd mag load 31. In that statement while it was intentional or not he brought up the slight effect of magazine spring tension on the carrier as well as everything else. Just never heard it put that way before.

 

[someguy2800]

CMMG RDB and Thompson Autorifle are nothing alike actually. The Autorifle is an example of 1-piece delayed blowback mechanism, and I was tempted to include it above alongside Reising. The CMMG RDB action is a 2-piece, like MP-5 or FAMAS. The key difference is that the acceleration in a 1-piece system applies to the whole mass. Therefore, the low acceleration required for a short travel of the case requires a great disadvantage. But in a 2-piece system, the whole point is that the blowback mass moves faster than the bolt, and it can cover a greater distance under acceleration than what is permissible for the bolt. This is they key element present in RDB and that Autorifle lacks.

The auto rifle is a 2 piece system. There is a brass piece behind the bolt that is accelerated rearward by camming action at a faster rate than the bolt. See video above at 4:10

 

[gotboostvr]

slight thread drift here and at first I really didn't understand that nuclear was trying to say



Then it dawned on me he was using a computer term in a gun applications. Then it became clear his "downloading" was 1 less than the max qty of a magazine ie 25 rds mag load 24, 32 rd mag load 31. In that statement while it was intentional or not he brought up the slight effect of magazine spring tension on the carrier as well as everything else. Just never heard it put that way before.

That a pretty common term for the practice, fyi.

 

[halfmoonclip]

The word "tend" means that it does so sometimes. But in this case the action always delays the opening.

Uh-oh, we're debating the meaning of "is".
Actually, for me, in this context, "tends" says it somewhat retards the opening of the bolt. It's not an intermittent thing.
We're not disagree here.
BTW, the Blish lock thing is typical of discussion on locking systems; what they accomplish in theory, and what they do in reality, is really tough to judge. Modern, high speed photography, may help answer those questions. If anyone is looking.
Moon