Colt Hydraulic SMG/DOE 9mm buffers

[secondofangle]

Hey, guys - there's an old thread that's locked from 2009 about these buffers, mixed reviews. Anyway, I picked up two from a dude on GB ($200 each) and when I compress them (at any rate/force I can apply manually) I don't feel anything like a "hydraulic" action - just a spring action. Because these are known to leak the fluid, I wonder if I've been had, even though they were described as "NOS" and with "strong" compression. Should I be able to feel the hydraulic action? I'm tempted to run one in my SMG and see if they "work" compared to a variety of other SMB buffers I have (original, "X" marked from SAW, and 2-piece) - to see if there's a difference. But I have only test fired my SMG lower once, so I don't want to put it through the paces only to discover that I got old duds.

Any advice/insights appreciated. If I do fire them, I'll report back.

 

[A&S Conversions]

Sorry that I can’t help. Mostly because I have never seen a Colt 9mm carbine length hydraulic buffer. The only one I have seen is the Colt hydraulic rifle length used with the green spring and the LMG upper. I would like to see the Colt 9mm hydraulic buffer.

Scott

 

[TSPC]

Sorry that I can’t help. Mostly because I have never seen a Colt 9mm carbine length hydraulic buffer. The only one I have seen is the Colt hydraulic rifle length used with the green spring and the LMG upper. I would like to see the Colt 9mm hydraulic buffer.

Scott

One of these I assume:

 

[SecondAmend]

A human cannot generally move forcibly and quickly enough to manually actuate the physical hydraulic damping aspects of a hydraulic buffer. You need to either test the buffer on a test rig that is specifically designed for such testing or shoot with it. Rapid actuation of the buffer is needed to rapidly force the hydraulic fluid through the ports/orifices. Maybe a Mike Tyson punch would work.

As an example of what I mean by your not being able to test it manually, consider the KynSHOT RB5100 Adjustable Shotgun Recoil Buffer. I have a couple. There are three settings. "0" is spring only, "M" is medium damping, and "H" is heavy damping. Regardless of where the damping setting is, a person pushing on the buffer only feels the spring force. But shooting proves that the buffer produces the desired hydraulic damping.

FWIW, I've had excellent results in AR-15/M16 9mm shooting with the B & T AR9 hydraulic buffer when compared against five different conventional AR buffers and six other AR hydraulic buffers, none of which were the Colt 9mm hydraulic buffer. I've never bought the Colt item as I've been concerned that the seals, probably being rather aged, have stiffened to the point of reduced capability or failure.

MHO, YMMV, etc.

ETA: And by excellent results, I mean that the B & T AR9 hydraulic buffer resulted in the lowest full auto, rate of fire. With a 5.5 in., 9mm barrel, 17.1 oz. direct blowback BCG (standard small extractor, Glock cut 9mm BCG with KAK Industries tungsten internal weight), standard length buffer tube, no spacer, and standard recoil spring shooting Federal AE 115 gr. RN copper covered ammo, the ave. ROF measured 655 RPM.
AETA: The weight of the B&T AR9 is listed as 6 oz., but my scale reads it as 6.1 oz.

 

[hkg3k]

Hey, guys - there's an old thread that's locked from 2009 about these buffers, mixed reviews. Anyway, I picked up two from a dude on GB ($200 each) and when I compress them (at any rate/force I can apply manually) I don't feel anything like a "hydraulic" action - just a spring action. Because these are known to leak the fluid, I wonder if I've been had, even though they were described as "NOS" and with "strong" compression. Should I be able to feel the hydraulic action? I'm tempted to run one in my SMG and see if they "work" compared to a variety of other SMB buffers I have (original, "X" marked from SAW, and 2-piece) - to see if there's a difference. But I have only test fired my SMG lower once, so I don't want to put it through the paces only to discover that I got old duds.

Any advice/insights appreciated. If I do fire them, I'll report back.

I had forgotten I had one of these till I saw your post. With the exception of the Colt LMG full length hydraulic buffers, neither the Colt 9mm DOE hydraulic buffer or the commercial hydraulic buffers I've used have what a would call a lot of "resting hydraulic resistance."

The Colt LMG buffer is very stiff at rest, especially in comparison to all the others. The DOE buffer is not quite as stiff as the Enidine and Kynshot buffers, but has a slightly longer throw. I found my DOE buffer in my spares box. I can't remember if or how much I used it as I probably purchased it over 20yrs ago. I wound up settling on a heavier / longer hydraulic buffer which provides a shorter bolt throw and is only suitable for pistol calibers. As SecondAmend points outs, the harder / faster a hydraulic buffer is compressed, the more effective the damping action.

I can tell you my DOE buffer weighs 4.8oz. Dennis Todd shows them on his website, he's been a Colt part vendor for as long as I can remember...you might give him a call or email and ask him about your buffer before you decide to give it a try.

Good luck...

 

[amphibian]

Here is a link to my really old straight blowback 9mm M16 I used to run 20+ years ago: https://c3junkie.com/?page_id=752
Picture below from my site above. That Colt hydraulic ended up leaking and bled hydraulic fluid all over my gun.
I think I read that Colt didn't make them and those were contracted out by another vendor.

 

[A&S Conversions]

One of these I assume:

View attachment 40741

Thank you for the picture.

One of these I assume:

View attachment 40741

Thank you for the pictures guys. I have had a Garrison DOE clone made from a Colt 9mm upper and a pristine set of M231 hand guards. I had no clue until this thread that Colt had made a hydraulic buffer for the DOE. “amphibian” thank you for the link. Overall this forum tends to move slowly. But the UziTalk community has been so knowledgeable and supportive in my journey to learn more. So much better than the drama on some other sites. Thank you all for sharing your knowledge and experience. I need to try “amphibian’s” Kynshot/Tubbs combo with the DOE clone with the M60Joe ramped and tungsten weighted Colt bolt.

OP good luck with your two Colt hydraulic buffers. With the information for this thread I would think you could try one of the buffers in your Colt 9mm lower. If the two buffers look new, you could weigh them with a fine scale. If they weigh about the same, what would be the odds that the same amount of oil leaked out of both buffers? Did they come to you in Colt boxes? If so was there any oil stains on the packaging? Let us know how you make out.

Scott

 

[secondofangle]

smart ideas from all. I especially like the "weigh them"

I'm going shooting in the desert tomorrow, and I think I'll throw a new upper on that DOE lower and give one of the buffers a run.

I inquired with Dennis Todd (was going to buy another two and double down!) but never got a response.

I'll post a video on uTube, since there are none, and link it if it comes to fruition.

Again thanks for weighing in guys!

 

[secondofangle]

They both weigh 140 g which is 4.9 ounces

And yes, the top one has some staining which looks like from storage. The plunger ends are pristine, and I doubt they have been fired.

 

[amphibian]

I bought mine from Dennis Todd 20+ years ago. Again, I think the Kynshots are way better as there are different spring rates available as well as lengths for different applications.
Here are some links on my site regarding the tuning I've done regarding 556 and the CMMG delayed blowback setup. I use the Kynshot RB5007 for about 95% of all my full auto configurations (including 9mm and 556).
https://c3junkie.com/?page_id=325
https://c3junkie.com/?page_id=977
https://c3junkie.com/?page_id=1733
https://c3junkie.com/?page_id=1403

 

[secondofangle]

OK, I don’t have a shot timer, but I can tell you that the difference between running it with a ramp to bolt and a 7 inch DOE upper appears to be very minimal between the current two-piece SMG buffer and colt hydraulic buffer, which I tried.

I can edit the video down to 1 hundredths of a second, and I timed it from the first round muzzle flash to the last bullet/case exit in a 20 round burst

When I do the simple math on the amount of time it took to empty the 20 round magazine, the rate of fire is about 865-875 with both of them.

So if there is a difference, it is within the measurement error in 1 hundredths of a second. Of course, I think the two-piece bolt is heavier, and over the years that may be the reason Colt went that direction because why screw around with a problem, prone hydraulic buffer when you can just make a heavier, two-piece bolt and achieve the same result.

When I get home, I can upload some videos to YouTube to share with you. But I’m not sure you will get a lot of more out of them than what I did. Perhaps I should’ve used slow motion, but looking at them in real time you really can’t notice a difference.

(I have edited this post 40 minutes after I originally wrote it because I realized that not all of the muzzle flash and bullet exit was recorded in the video and I had to adjust my timing to capture the full 20 round burst. Previously, I thought there was a 6% difference in favor of the hydraulic buffer, but that difference went away on closer inspection of the video.)

 

[SecondAmend]

Here's a link to a Small Arms Review article about the Colt 9mm that includes discussion of the Colt hydraulic buffer and rates of fire:
https://smallarmsreview.com/the-colt-9mm-nato-smg-carbine

 

[secondofangle]

 

[secondofangle]

My conclusion is that there is no sense messing around with antique hydraulic buffers.

I will save them as collectors items to go with my DOE uppers. But I don’t think I’m going to buy any more of them.

The current issue two piece SMG buffer does just as well without the worry of malfunction

Now those other modern buffers that have been linked above, have my attention

 

[A&S Conversions]

I think that the buffer spring is more of an issue. The higher the spring rate, the higher the rate of fire. The advantage of the flat wire spring is that the bolt needs a certain amount of force to strip a round from the feeding device, chamber that round, and fully go into battery. The flat wire spring fits more coils in the same space. So each coil has to impart less energy per coil. So if a standard carbine length spring has to give 9 pounds of force at rest on the bolt face to be fully in battery, then to pull the charging handle back so the full throw of the bolt is achieved, each coil has more compression than the higher coil count of the flat wire spring.

“amphibian” has gone over this in his research. So the higher spring pressure of the standard spring at the back end of the throw of the bolt, causes the bolt to go back into battery quicker than the flat wire spring. The increased speed of the bolt causes a higher ROF and tends to cause increased bolt bounce issues.

I have to admit that the carbine length Colt hydraulic buffer is new to me, but I am familiar with the rifle length Colt hydraulic buffer and green rifle spring used with the Colt Light Machine Gun upper. That buffer and spring commination slows the ROF considerably. I wonder if the DOE hydraulic buffer was also designed to be used with a lighter spring like the hydraulic rifle buffer and green spring used in the LMG upper? Just a thought.

Scott

 

[amphibian]

What is your goal w/ the DoE? Are you trying to slow it down or smooth it out or both?
Here is a picture of some testing I did with the Maxim RDB (Roller Delay Buffer)

I ran it in a DoE clone I built as pictured below but felt the cyclic rate was still too fast for my liking. It is smoother than straight blowback though.

 

[secondofangle]

only goal is to get it set up correctly, functionally, and as “Colt” as possible so if I ever go to sell it I can advertise it properly. I will rarely shoot it, but if/when I do I’d like it to run “nice” like my MP5

 

[amphibian]

only goal is to get it set up correctly, functionally, and as “Colt” as possible so if I ever go to sell it I can advertise it properly.

Maybe someone can correct me here but I don't think the original DoE uppers used ramped bolts back then. As you probably know, non-ramped bolts are more prone to breaking hammer / trigger pins.

I will rarely shoot it, but if/when I do I’d like it to run “nice” like my MP5

No offense but I think those two are contradictory, unless you are thinking you want a DoE 'factory' config and a non-factory DoE config for 'smooth' shooting.
I personally think all straight blowback 9mm M16's will never run as 'nice' as a roller delayed blowback MP5. I don't care what buffer you use (even the Maxim Roller Delayed Blowback buffer) it will never be as smooth as an MP5. Although, I think the Maxim is the best option for a factory DoE upper but still pales in comparison to an MP5.

Myself and several of my friends have wanted a smooth shooting 9mm M16 to rival the MP5 for 20+ years.

I discuss all the known options I can think of in this link here: https://c3junkie.com/?page_id=361

If you read all that, you will see that I finally have what I've been after for 20+ years and now have my 9mm M16 surpassing my MP5 but it required custom work as documented here: https://c3junkie.com/?page_id=1733
I have built over a dozen for friends and people I don't know that are all running them in full auto and we all prefer them over our MP5's.

I have always been a sucker for the gook looks of the DoE upper and tried to bring new technology with the old school looks and did below:

That project was a failure above. I know I could build out one of my hybrid Dissent's using a DoE handguard but the problem is I need a thicker upper to machine a new cam pin slot and now it wouldn't have the DoE look anymore so I gave up and now built this out.

The looks of the DoE but in a full auto 22LR setup.

 

[secondofangle]

Noted, thank you!

 

[secondofangle]

I like your idea of getting an AR-15 conversion so you can shoot a lot and not worry so much about the receiver

OTOH, great argument for a RDIAS