I had been working on this magnetic buffer project for a few months, and as of a couple of weeks ago, I arrived at a configuration that I'm happy with for the time being. Since u/AddictedToComedy made a post today about a very similar project, I figured I might as well add to the conversation, and perhaps even address some of the concerns that were had in his thread.
The AR9 that I used for all of my testing is a CMMG RDB 9mm FE build with the following:
-CMMG 8" barrel with FTN5 PCC Flow (note that the lugs on my barrel extension are pretty well worn in after about 7500 rounds, and I strongly suspect the radial delay is a bit less effective than it was when the lugs were brand new, so keep this in mind if you are doing a brand new build and decide to test this buffer system).
-Lightened and long-stroked BCG with titanium FP (8.8oz total)
-JRC 8.5" buffer tube
-V Seven Weapons Systems titanium castle nut and end plate (more on this later)
The buffer system is comprised of:
-Neverwear Warthog spring
-Two 25mm X 10mm cylindrical N52 magnets
-0.1" and 0.2" thick 3D printed TPU spacers as shown (to adjust stroke length and cushion the magnets)
-Standard carbine buffer body with 932 bronze buffer weights (one cut slightly short to replicate the internal sliding length of a Vltor A5 buffer). Total weight was 3.19oz.
The ammo used for testing was:
158gr RNFP with 4.0gr CFE Pistol, 935fps
The mags used for testing were printed clones of the CMMG mags.
The buffer system makes use of Lenz's law which basically states that a changing magnetic field (caused by the movement of the magnets) induces an eddy current in a conductor (the aluminum buffer tube) that opposes the movement of the magnets.
It is important to note that this effect is completely separate from magnetic attraction and repulsion. Unlike the Miculek magnetic buffer, this system does utilize any movement between the magnets themselves, nor does it arrange them with same poles facing each other in order to make them repel.
The end result of this system is that the reciprocating mass is slowed during both the rearward and forward strokes of the BCG. Because of this, I opted to stop using the Tubb 300BO spring that I had used for early testing, because I find that it was too weak to reliably push the BCG into battery with the eddy currents slowing it down. I ended up replacing it with a Neverwear Warthog.
After having broken two hydraulic buffers, I decided that I wanted to stop using them. Early testing included some tests of a RB5007 with various magnet configurations placed in front of it, but I found that the magnetic force would cause the plunger to stick in the depressed position, which certainly wasn't ideal anyways.
After ditching the hydraulic buffer, I switched to a standard carbine buffer. I felt that it was necessary to preserve the dead blow functionality of the sliding weights, even if it meant I couldn't get the reciprocating mass down as low as I wanted. The first problem that I noticed with that was the fact that the internal sliding weights, whether made of steel or tungsten, would be attracted to the magnets, preventing them from sliding freely and functioning as intended. The solution was to fabricate some 932 bronze weights which have both low conductivity and magnetic permeability, and therefore do not interact with the magnets. I also tested some aluminum weights in the interest of making the reciprocating mass as light as I could, but I ended up sticking with three bronze weights for reasons that I will show below.
Another issue I had to address was the fact that the magnets would be attracted to the castle nut and end plate, which were both made of steel. This wasn't a huge problem, but I noticed that I would experience occasional short strokes (at least with my subsonic 158gr ammo), which I suspected were caused by the added resistance on the BCG by the magnets trying to stick to these parts. After replacing the castle nut and end plate with titanium versions, I no longer had these short strokes.
So how does the end result shoot? Pretty damn great if I do say so myself. The recoil feels exceptionally soft with very little sight disruption. Reliability has been perfect in the 1000+ rounds I've fired since setting up this final configuration.
I also have ROF data for those who are interested in FRTs, DIASes, M16 lowers, and such.
With the 3.19oz buffer described above, NO MAGNETS, and a 1.24" long solid steel weight with the same cross section as a Kynshot spacer weight. This setup had a total reciprocating mass of 16.14oz, and did 789 RPM.
As another point of reference, I have data with a RB5007 buffer with standard carbine spring and no other weights or magnets, which resulted in 14.8oz total reciprocating mass, and 723 RPM.
Below are the results with the two magnet stack described earlier:
With one bronze weight and two aluminum ones, the buffer weighed 2.2oz, total reciprocating mass was 13.45oz, and ROF was 670 RPM.
With two bronze weights and one aluminum weight, the buffer weighed 2.76oz, total reciprocating mass was 14.01oz, and ROF was 640 RPM.
In the final configuration with 3 bronze weights, the buffer weighed 3.19oz, total reciprocating mass was 14.44oz, and ROF was 616 RPM.
