I think this may be the best possible setup for taming AR9 recoil. I did not expect the results I got. I've tried a bunch of different things with varying degrees of success, but this was completely different.

With help from all the high speed video (currently doing 1000fps bolt bounce and spring resonance tests) and the Overmass Project work I did recently, I was able to put together a configuration that is, in my opinion, the ultimate "gentle recoil" simple-blowback 9mm AR. Double-taps are easy and I don't lose the dot even for a moment.  It's not as gentle as an MP5, but for less than $180 in parts, I was stunned at how good it felt.

It's not .22 rimfire gentle, that's just not possible. It's still a solid push, but all of the snappyness, harshness, punchyness, etc. typical from a 9mm AR is gone. If anyone asks for a configuration for their girlfriend/wife/daughter, this is the one I'm going to recommend.

In a nutshell, it has the recoil advantages of heavy mass, hydraulic shock absorption, and no noticable spring noise.  No bolt bounce at all, high speed video in the article in the link.

Here's the recipe:

- Just Right Carbines extended buffer tube. This tube is 1.5" longer internally and externally, and is the perfect size for a 9mm AR bolt to use these parts and still have the correct travel. Finding this tube was the key to making this combination of parts work.
- Kynshot RB5007 6oz. hydraulic buffer. The heavy dampened RB5015HD should work too.
- Two Kynshot 2.5oz. spacer weights (R15015098), which add 5oz. in mass, giving 11oz total buffer mass.
- Strike Industries flatwire carbine spring. Other brand carbine-length flatwires should work, too. (ETA: It's TIGHT. Oil the buffer body.)

A competition-shooting colleague uses a similar, but different, setup for his competition rig.  Heavy damped RB5015 and 1 Kynshot mass in a short stroked system.  He has a CMMG RDB and says he feels no significant difference between the two. My configuration has an additional 2.5oz and is full stroke, slowing the recoil impulse even more.

Here's the full writeup, with parts links: Gentle Recoil 9mm AR

I am NOT affiliated with any company and I don't get any kickbacks. There are NO share-a-sale links or any of that crap. This is my hobby and it's all completely sponsor-free. I'm doing this for fun, to learn, and help people enjoy their AR9's.

I'm going to do more testing on this configuration, but I was really impressed.  It felt like a completely different gun.


UPDATE: Range report, Dec 8, 2022

I wanted to make sure I wasn’t misleading anyone (or myself) about how the recoil felt, so I went to the range again. This time I brought three 9mm PCC’s.

- My 27oz. heavy mass 9mm blowback, which was my most gentle recoiling setup so far. MidwayUSA 11oz buffer, DI Enhanced carbine spring.
- The Gentle Recoil 9mm blowback, with the JRC tube, hydraulic buffer, 2 kynshot spacers, 25.7oz total mass, and flatwire spring.
- An MP5 - the gold standard for 9mm PCCs.

I loaded them all, set them on the bench, picked them up one at a time, and cycled through them over and over, taking 2-4 shots each until they were empty. I was able to get direct side-by-side comparisons of their performance.

Recoil perception is all subjective, but the best way I can describe the difference is: the Gentle Recoil setup feels like it has the same smooth-push impulse of the MP5, just there’s more of it. After comparing them side-by-side, the recoil characteristics feel very similar to an MP5 to me, just with more push.  The recoil is "heavier" but not "sharper", if that makes sense.

The 27oz felt harsh, snappy, and punchy compared to both of them. Frankly, I don’t even want to use it now that I’ve felt how good the recoil can be in an AR9.

I've added all the other details such as the effect of barrel length, removing one spacer weight, spring noise differences, and dot movement to the article on my site.  I'm not going to paste it all here, so please check the bottom of the article if you're interested in those details.

I’m now a firm believer in this system. More testing will be needed to see  how it holds up over time, but I’m going to upgrade my other guns to use hydraulic buffers + spacer weights once time and funds allow it. If it holds up, this is going to be my go-to recommendation from now on for anyone who wants to tame the AR9 recoil.

They'll be pretty clever if they can compete with roller-delayed blowback.

I agree. I'm waiting for a friend of mine to get a RDB so I can do some comparisons. Next range trip I'll compare it to my MP5, but I expect it'll be no contest.

BTW, there is no "they", this is a combination of parts of my own concoction based on everything I learned about the platform through research and experimentation. I should probably clarify that in the original post.

More info: Blowback9.com - I am NOT affiliated with any company and I don't get any kickbacks. This is my hobby and it's all completely sponsor-free.

So I bought a Strike Industries 'AR Pistol' spring trying to save some bucks over the Tubb Flatwire 300BLK spring but the Strike's ID is too small for the Kynshot to go into.
So wondering if they use a larger diameter for the Carbine length you have.

Thanks for the information.

We really need stickies at the top of the page for stuff like this.





.

It's tight. I lubed the outside of the buffer with CLP and slipped it on. Doesn't seem to affect functioning. I have high speed video of it through a skeletonized buffer tube and it looks fine when cycling.  I have a Botach carbine flatwire as well, and it's the same, very tight.

I need to get a couple more flatwires to test, but the budget is shot for the year.

What about the JRC extended tube with an A2 buffer and spring ?

Cheapskates Unite !

Tubb makes a standard 5.56 buffer spring and a 300 BLACK buffer spring.
Is one recommended over the other for a 9mm PCC?
I currently have a Kynshot buffer and “Red” sprinco spring.

Thanks

RB5005 or RB5007 buffer
Tubbs Flat wire spring
CMMG RDB Bolt/Barrel

That’s pretty much it.  It’s literally almost MP5 smooth.  Seriously.  I actually run a Griffin SOB buffer because I like the RPM a tad faster in a machinegun for fun.

IMO you don’t even really need the heavier 5007 or heavy damped ones if you’re running a delayed action setup like an RDB.  They’re just fine with ~5oz give or take.

As mentioned on my site:https://c3junkie.com/?page_id=280
I run the 300BLK Tubb in my full auto CMMG RDB.  The 556 Tubb goes about 30 RPM faster which  I don't want.

This interests me, I'm playing with a 4.5" FX9 and working up a design for a dual-mass, ball-lock delayed buffer.
Still a work in progress, just want to get more dwell time for less port pop without having 1.5+lbs of bolt/buffer mass.
The bolt is about an inch shorter than an AR9, and i would like to use a Q shorty stock.

Well, yea... RDB is a mechanical delay. Mechanical delay systems always have an advantage over simple blowback because they can work with lighter masses.  No big surprise here.

The surprise is how smooth this new configuration is for a simple blowback.  As I mentioned above, a colleague has an RDB.  According to him, compared to his blowback with the Kynshot/1 spacer weight/flatwire, they feel the same.  With the JRC tube and 2 spacer weight, the buffer mass is up to 11oz and the impulse is slower, which translates to even less perceived recoil. Plus it costs less than $200 for the parts.

I'm going to get back out to the range today and play with it some more, and compare it side-by-side to another build I have and a roller delayed.

I have high speed video of the Kynshot with both flatwire and Sprinco Red through a skeletonized buffer tube. I used a Strike Industries 5.56 carbine flatwire. The flatwire settles much faster, and the extra force of the Red spring is really unnecessary for 9mm.  Here's the video link if you want to take a look.  42 seconds.

That is awesome...you may have seen my slo-mo vids I did at 1000 FPS with a cheap Casio...crap resolution....
I'm jealous I need to get that camera you got.  I came to the same conclusion about the flat springs and have been praising them for a few years now.  

As a competitive PCC shooter I’ve tried about everything to find the smoothest recoil impulse. Adding weight made it feel benign but it translates to increased and less predictable muzzle movement.

Standard short stroked system with a Blitzkrieg buffer was objectively the best running 135pf 124’s.

I’ve since converted all my AR9’s to roller locked and never looked back.

With the Scheel's buffer?

Big update posted at the top.

Yup.

OP, I appreciate you doing the research and taking the time to post it in multiple locations.

Particularly given the ejector issues CMMG has had w/ their delayed blowback system, this would seem ideal for a suppressed house gun as even if the hydraulic buffer fails, the gun can continue to run, albeit w/ a sharper recoil impulse.

I’d be shocked if you could get a Blitzkrieg to fail.  I’ve got over 100k on one and probably close to 80k on another.

im in ne colorado with an rdb if you wanna play

i like the rdb as it has less extra "unique" parts

@45-Seventy

What is your exact spring set up?  Buffer spring color and the springs in the buffer, and position of those springs?

Suppressor use?

For recoil mitigation of any shouldered firearm, I like to use a gel type butt pad.

MHO, YMMV, etc.  Be well.

None of my race guns are set up for a can.

My USPSA guns have a 10” rifled barrel with 6” lightweight P/W comp. 135-138 PF ammunition with 124gr slugs.
Light spring in position 1, heavy spring in position 2, medium buffer spring, short stroked.
Right now I’m experimenting with using the TACCOM air buffer to short stroke the system and it’s working amazing.

Steel Challenge is a ultra light barrel with 5” of rifling and full length aluminum tube for 16” OAL. 105 PF ammunition, 100gr slugs.
This has light spring in position 2, medium rate buffer spring, full length stroke.

For an AR9 predicable and minimal muzzle/dot movement is far more important than just benign recoil impulse.

Which is why I try to minimize reciprocating mass, which in turn, may cause a higher horizontal recoil impulse at the buttstock, eh.

Disclaimer:  I have no affiliation with or financial interest in any vendor or manufacturer.  I am not a competitive shooter or a blogger who receives any form of compensation for endorsements or favorable public or private comments.  I do not have a website or online videos.  Use of vendor and/or product brand names, if any, is for informational purposes only; and products or services were purchased by me from regular commercial sources.

Best of luck.
MHO, YMMV, etc.  Be well.

Fixed it for you. If you don't believe me, ask my wife.  If the recoil impulse is harsh it gets left at home.

How does the Scheel's buffer affect charging?
Does it take a good yank?
It doesn't unlock like a typical roller locked bolt before primary extraction.

Neat

The AR Pistol i built was pretty brutal with a shockwave blade... That fucking hard plastic corner man lol.

Stock weighted BCG with a KVP 9mm heavy buffer. I also tried a 308 spring.

I think a linear comp kinda made things a bit worse but not by much

That was a lot of mass chonking back and forth.

It does. It’s weird in that it takes noticeably more effort to unlock, but then it’s easier.

That's what i figured.
The system I'm working on may include a captive linkage to begin unlock before the bolt moves when pulling the charging handle
Would be more akin to the function of a Stribog A3 dual-mass delay, but in the buffer tube.

@Droppoint

What muzzle device are you testing with?

The reason I ask is that I went on a similar journey in 5.56 for work. I wanted to replace my pig of a Sig 556 at 14 lbs with a >7lb rifle that had (almost) the same recoil impulse.

I took some ideas from 3 gun competition rifles and came up with a combination that has gone through my testing and an instructor school (1500 rnds) flawlessly (did run it wet though). I ended up using a Precision Armament M4-72 comp which really needed a ton less gas. From the beginning I had an adjustable gas block so it was a non issue.

I am curious about muzzle device and blowback operation. Theoretically they work when the pressure in the barrel/chamber has already dropped or is dropping dramatically. I know IDPA PCC shooters run some big comps.

I am just wondering about the intersection between your recepie and a gnarly comp.

@Digger440

All my barrels are set up for tri-lug, so pretty much bare muzzles.

Last I saw, the consensus was that 9mm really doesn't produce enough gas for most (any?) comps to have a significant effect. Those big PCC comps may just be acting as muzzle weights. I could be wrong, though. Other folks may be able to provide further input on that.  I'll need to do some research on the topic.

I've had 3 'fail'....it didnt' leak.  Just the head of it fell off.  Each time they replaced it, they said they made improvements to prevent it happening again and I could see some differences which I think I've posted before.  Since then, I haven't had one fail again but I don't think I've shot as much since then either.

We had a guy on the HiPoint forum that was having problems w/ his 9x19mm Yeet Cannon.  He had screwed a giant brake on it, and was having rounds stovepipe out of the mag, instead of the usual HiPoint problem, nosediving into the feed ramp.  We suggested he try it w/o the brake, then HPFF deleted his threads & banned him.

A properly designed comp absolutely works to stabilize the muzzle and reduce movement. My primary USPSA stock has a 10” barrel with 6” comp. While only the first inch or so is actually effective you can clearly see vented gas in videos, particularly in slow motion. Running a similar barrel without a comp is noticeably less predictable.

Good info! Which ones work besi in your experience?

I'm confused by this part...


9mm Bolts are shorter, not longer then standard 556 BCG's so why would I want a longer buffer tube? I actually used a buffer spacer to limit the rearward movement on my 9mm AR with a standard 9mm buffer. Is this extended tube needed to run the hydraulic buffer you are using?

Yes, it can be confusing. 9mm bolts need 3" of rearward travel if you want LRBHO.  5.56 need 3.75".  A 3.25" carbine buffer provides 3.75" of travel in a 7" carbine tube, too much for 9mm, which is why you need a buffer spacer or a 4" buffer.

A JRC tube is 8.5" internally.  Add a 4" hydrauilic buffer and two 0.75" weights, and you're taking up 5.5", leaving 3" for bolt travel.

Gotcha

The TACCOM Enhanced bolt is designed to allow for LRBHO when short stroked.

That's going to be part of the next phase of this project.  I've got a combination of parts that will all fit in a carbine tube, maybe even with a standard bolt, but the Taccom testing is going to be first.  Just need to buy everything and start testing.  Probably in January.

I used to run a pretty light load of Power Pistol as the competition ammo my girlfriend and I both used in PCC division and while she was shooting with her 16" barrel I could see flames coming out of the ports of the brake.  That was enough to prove to me that the old wisdom that 9mm will fully burn its powder in 10" isn't true.

I think the point of that saying is that there is little to no velocity advantage to barrels longer than ~10" for service pistol calibers.
All that hot gas doesn't suddenly cool before exiting the bore, regardless of length.
Power Pistol is also a very flashy powder.

I have not tried the Scheel buffer or the hydraulic buffer but have tried the Taccom Magnetic Delay Recoil System and am very impressed with the recoil and dot movement. I have run it with Taccom 10/16, ULW and ULW mid brake barrels.  Ii tamed all three barrels for movement and reduced the impact recoil of the guns.  This recoil buffer is also very tunable for different loads from light steel challenge reloads to factory 115gr ammo.

I tried my stupid short 2.5" barrel and a 5.5", which is the longest I have.  The 5.5 did have a little more recoil, as expected, but it was still a lot better than a similar weight deadblow buffer, at least to me.

I didn't try shooting it as fast as I could.  I did several quick double-taps, but I wasn't trying to race.  One more thing to test for next time - I still have it all build and ready for another range trip.  It's supposed to warm up, so hopefully next week.

You described the order of the parts perfectly:

Typically for a blowback system, long barrels tend to have more recoil as the shell has more dwell time (the time that there is pressure inside the barrel pushing the shell on the bolt) putting more energy into the bolt. With more energy, the bolt tends to move faster, hitting the back of the receiver extension harder. Once the recoil energy is overcome, a heavier spring tends to accelerate the bolt group faster back into battery. The increased speed causes the bolt group to hit the barrel harder, driving the gun forward.

So ideally in a blowback system, there is the maximum amount of mass such that the action fully cycles and the weakest recoil spring so that the bolt goes back into battery slowly. Such operation tends to make function problems. If the bolt group has so much mass that the bolt group hits the ejector slowly, ejection will be weak. Possibly causing the shell to be knocked off the extractor but not thrown clear of the mechanism. If the recoil spring is too weak then the bolt will not have enough energy to strip the top round out of a fully loaded magazine. All the forces need to be balanced for proper function.

The MP5 mechanism seems to be the gold standard. I think that a big part of that is the mechanism diverts some of the recoil energy into the receiver. This allows the bolt group to be lighter than a simple blowback system. The lower the mass of the bolt group moving around in the gun, the lower the energy in the bolt group. If there is less mass moving inside the gun, that lower energy tends not to move the gun. Whether simple blowback or delayed blowback, the bolt group needs a certain amount of speed to function. If two bolt groups are traveling about the same velocity, but one has more mass, the one with greater mass has more energy. The more energy in a bolt group the  greater the force acting on the gun.

Scott

Scott

Well said! Great explanation of how all the components have to interact.

I'll add, 9mm blowback appears to have much greater tolerances for barrel length, mass, and spring rate than we all seem to think it does.

My Overmass project found that a 2.5" barrel could consistently cycle 115gr. range ammo with 37.5oz (21oz buffer, 16.5 bolt) and a standard 5.56 recoil spring.  The ejection of the 1st round was weakest due to, I believe, magazine spring pressure on the bolt, but after that ejection was better. No jams.

So far the Gentle Recoil project, with the slightly stronger flatwire spring (8lbs at bolt closed instead of 6.2) and 25.5oz cycles great with the 2.5 and 5.5 barrel and the recoil impusle is so much better.

BCA just came out with a bufferless upper with only 13.5oz of mass, no AR buffer, and as one person put it "an anemic spring", with a bolt impact rubber bumper at the rear.  No case blowouts or bulges reported and reports are that recoil is not bad at all.  This is much too light for a traditional AR receiver set, and generally considered too light for 9mm blowback, but it works.

One of my future experiments is going to include cutting down an AR spring to see how little pressure it takes to cycle 9mm AR's.  I'd like to do an "Undermass" project to see how light we can go before bulges/blowouts ACTUALLY happen, but it would require an entire new sacrificial build.  That's going to take a while to budget up for.

Very interesting. Seems like an attempt to build a GHM9 from available components.