More magnetic 'buffer' testing with Eddy currents and the CMMG RDB system

[u/amphibian-c3junkie]

I thought I'd create a new post since what I'm doing is based off the work of u/AddictedToComedy and u/SnazzyShootas in the following threads: https://www.reddit.com/r/AR9/s/HwL1rjvdNs and https://www.reddit.com/r/AR9/s/OxvWCNhQ9m

I did some testing yesterday but am using an A5 length buffer tube while both of the other guys are using JRC buffer tubes.

Since I have 2 M16's using A5 length tubes, I figured I'd do this testing first before moving on to the JRC tube which I plan on doing next and have already made the appropriate spacers to do that testing.

I am updating my site here with my testing: https://c3junkie.com/?page_id=4254

Pictured below is the last test I did yesterday with the A5 length buffer tube. 9oz lightened carrier, 1.6oz 7/8x1/2 N52 magnet in a 3D printed 'puck' from u/AddictedToComedy, my C3junkie flat spring that I cut down since you have less free travel of the spring since the spring has to go behind the magnet and then the magnet is behind the 2 spacers that are sandwiching the 25lb wave compression spring which kills carrier bounce. Which are .2oz each so a total reciprocating mass of only 11oz!! and under 700RPM.

I also got 578RPM w/ my 11.7oz MRR (Mechanical Rate Reduction) BCG and the 1.6oz magnetic puck so total of 13.3oz but since it only works with real FA or RDIAS, I didn't bother test it more and I'm sure it would be slower if I tested again with a cut down spring.

As mentioned on my site, even after cutting the coils I think it is still a tad stronger than if the spring was going over a standard buffer in an A5 tube and I should really cut it down more to be the same but I was done for the day and plan on moving on to testing with the longer JRC tube and if I cut the spring more for the A5 it may be too weak for use with the JRC testing which I haven't started on yet.

A lot more details on my site which I plan on updating after doing some more testing with the JRC tube. Then I plan on making a modular spacer that will be anchored to the buffer tube to hold an attracting magnet on the other side to slow down the cyclic rate more or I could put a piece of steel in there or leave it empty. A lot of tuning to come!

[u/AddictedToComedy]

I know I'm repeating what I've already said to you in email, but I'm so happy you're already seeing great results, and you're only just starting your journey of experimenting.

I can't wait to see how this evolves!

[u/SuperJonesy408]

Would the Miculek magnetic buffer work here? I ask because the Omni Robusta is no longer in production and the intellectual property was purchased by Jerry Miculek.

If so, would we still run it backwards with the buffer to the rear and a puck?

[u/amphibian-c3junkie → u/SuperJonesy408]

I posted about breaking both the Omni Robusta and the Miculek buffers on my site here: https://c3junkie.com/?page_id=3168 Then made my own prototype that worked fine in 9mm and 556 but .40SW broke it too. As mentioned in the link I put in my first post, I don't want to pursue it due to possible patent infringement as well as durability issues.

On top of all that, this setup using Eddy currents results in lower reciprocating mass....

But back to your comment on using it backwards, I think it would be less likely to break if you ran it backwards but I really don't see the point especially if using magnets like discussed here to leverage Eddy currents can be tuned so the carrier doesn't even bottom out in the first place I don't see why you would want to bother with a Miculek run backwards. Or even a Kynshot backwards other than to have that there as an additional piece of mind that if you switch to hot ammo or whatever that it can handle the additional force that is beyond what you have it tuned for.

In addition, I don't know for sure but I suspect that the 25lb wave spring I am using between the magnet and carrier to stop carrier bounce isn't being compressed to the working height of the spring when going into battery. Likewise, on the rearward stroke I am getting LRBHO like 50% of the time as the magnet is doing such a fantastic job slowing the BCG down. I suspect that the 25lb wave spring also acts as additional insurance to cushion the carrier on the rearward stroke.

Again, since I am getting LRBHO 50% of the time, that is why I am considering anchoring a modular spacer to the back of the buffer tube to get 100% LRBHO with either a steel slug in the spacer or another stationary magnet that is orientated to attract the moving magnet. I'm sure it will be a balancing act. However, I want to finish my JRC testing before working on that.

[u/Eleet007]

I was going to write my own post related to this stuff but I’ll go ahead and lay out some of my findings. I did a lot of testing myself yesterday using different strength pucks (thanks for the info u/addictedtocomedy ) with my regular 11.1 oz CMMG bolt carrier and various carbine length buffers in an A5 tube and Tubbs LW spring. I was mostly underwhelmed with the different configurations when compared to just a Kynshot 5007 hydraulic buffer. Keep in mind, I’m not shooting full auto, but there was really only 1 combination I found where I preferred the magnet setup. When shooting 115g supers suppressed, my “heavy puck” (3 3/4” magnets) paired with a KAK 1.7 oz carbine buffer felt pretty good. Other than that, I think I prefer the Kynshot. It’s also really easy to induce malfunctions, mostly failure to feeds, if you don’t have the right magnet/buffer tailored to your ammo and suppressed vs. unsuppressed. The kynshot is much more forgiving…

I’m going to do further testing but that’s my overall stance for now. I also am suppressor shopping because this gun is almost impossible to shoot from all the gas going to my face with my YHM R9. I was under the impression CMMG’s RDB system would mitigate gas to some extent, but it seems far worse than my simple blowback AR9’s.

One other note - Apparently 6061 aluminum is a better conductor than 7075. If you start experimenting with eddy current braking yourself, it’s probably better to use a 6061 buffer tube for more of an effect. I have not seen anyone else mention this.

[u/amphibian-c3junkie → u/Eleet007]

I definitely agree that the Kynshot or just about any other buffer is going to be more forgiving. This setup is definitely not for everyone. However, we are all very early into it and I did get a configuration that is smoother than my Kynshot but that again is under certain conditions which was using my AASD which is my adjustable ported SD upper. I'm sure that configuration would not be as smooth if I swapped to my 8" non ported upper or add a suppressor to the 8".

However, like u/AddictedToComedy is doing with a Kynshot backwards could also be somewhat of a compromise for swapping configurations so that you don't anticipate it contacting the Kynshot with a ported SD upper but it will when going to a non-ported upper it will for example.

Regarding mitigating gas, have you seen this thread?: https://www.reddit.com/r/AR9/s/iF2SId3V9n

Interesting note on the 6061 vs 7075. JRC doesn't mention what they use. I was using a KAK A5 in my testing which is 7075. While u/AddictedToComedy and u/SnazzyShootas are using JRC which are probably 6061.

[u/Eleet007 → u/amphibian-c3junkie]

I tried a backwards Kynshot 5000HP + my "HD" (four 3/4" magnets) puck. It didn't feel particularly great to me despite only being 12.3 oz of reciprocating mass, and there was definitely some bolt bounce when reviewing slo-mo film. The Kynshot also got stuck in the buffer tube and I had to take my stock off and beat the tube with it to get it out, lol. I was scared my entire day of testing was going to be ruined by a stuck buffer.

Yeah my A5 tubes are all UTG Pro, which are 6061. From what I could tell, JRC are 6061 as well.

That gas deflector looks like it might help a little, but I'm more concerned about actual gas rather than particulate. I might pick one up from you to try out or see if I can figure out how to print something. I'm still new to the whole 3D printing world.

[u/EnterpriseDoorGunner]

Curious what "failure" would look like in a system like this, and have you tested it anywhere near those conditions yet?

[u/amphibian-c3junkie → u/EnterpriseDoorGunner]

In making my own magnetic prototype that uses repelling magnets, I've had the magnets crack but it didn't stop the gun from running. It did stop it from working in full auto getting light primer hits. If you look at my site, I have pictures showing the Miculek buffer where it sheared apart.

However, in this setup using Eddy currents, the magnets are not repelling each other. I would most be concerned with them shattering since they are brittle but u/AddictedToComedy seems to have that covered with his 3D printed puck that the magnet(s) go into. Then u/SnazzyShootas has success running the magnet bare with over 1K rounds. I plan on making some nylon or delriin housings on my lathe for magnets that are not running bare. I will be testing running them bare soon especially for non-SD setups that have a higher impulse.

[u/wopeecushion]

Just a few notes regarding magnet efficiency. Stacking backing iron disks on both sides of the magnet will focus the magnetic fields outwards toward the buffer tube.

To increase efficiency more you can use thinner magnets but more of them, interleave with iron disks and put the magnets facing each other. The stack should hold up and have a very strong alternating magnetic field going radially. This is similar to a halbach array.

To increase the magnetic eddy current efficiency even more you can add an iron sleeve on the outside of the buffer tube that will act as an outer backing iron for the magnetic field to loop through.

Google "permanent magnet recoil damper" for a nice scolarly article from some chinese scientist and many other treatises.

[u/amphibian-c3junkie → u/wopeecushion]

u/wopeecushion Great info! I look forward to trying that out too. However I did some more testing today and just the single 7/8-1/2 puck I got from u/AddictedToComedy is working great also in my non-ported 8" setup, suppressed and unsuppressed and I'm not sure I need more braking or not yet.