So after careful consideration I decided to go with the GLR Qwik-Lok Slimline retainer.
This was not my first preference as the look of the Bell grew on me over time, although out of the gate the Slimline was my first choice. However as much as I like the look of the Bell I believe that I may live to regret using it, but I know I won't regret using the Slimline. The fact is I know far too little about the Krushnic Effect, even though I read whatever I could find about the phenomenon in a couple of days and even made some inquires outside TRF resources.
At the end of the day no one was able to provide a firm answer and remarkably it appears that this particular effect could use a bit more study. As I indicated I have some ideas on how to mitigate the effect, or at the very least use it with more confidence, which I may do at a later date.
So on with the build. Over the last two nights I continued working on the fincan assembly. The first thing I did was to pass the Kevlar Y harness back through the holes in the top CR, and re-insert the pins. This was slightly challenging but very doable. The reason I assembled the top CR this was was because I did not want to create a stiff, weak point due to the epoxy that may harden and crack over time. I still need to dab a small bit of epoxy on the pins so they don't fall out. Next I sanded the lower CR on it's top and bottom, as I did with the top CR. Then I mocked up the assembly so I could mark where the CR, fins, and retainer would eventually be located. Once I was confident in my measurements I disassembled everything and prepped the tube with 100 grit. Where the CR and retainer attach I sanded perpendicular to the length of the tube, and where the fins attach I sanded along the length of the MMT. Then I slid the CR back on.
One advantage of the slimline retainer for this build that I had not considered is that I can insert it assembled onto the MMT into the tali-cone from the top and it slides right through. This will allow me to assemble things in a different order than I had originally pictured. The gap between the retainer and the aft opening of the tailcone is almost zero, it fits very well with no play at all. However the MMT is significantly smaller than the ID of the retainer. To fix this I took some masking tape and applied it to my cutting board which allowed me to use the grid pattern to cut even rows of tape that I stacked 7 high times high times by 3.
This gave me three masking tape spacers that I put on the MMT 120° apart.
I then test fit the retainer and it was slightly sloppy. I want the fit slightly tight but not overly, otherwise when you slide the retainer on you can slide the tape around. So I added one more piece of tape per spacer, making up 8 layers.
Next I mixed up a batch of JB Weld and applied it to the tube in between the tape spacers at a thickness that would fill the entire cavity and squeeze out the excess, but not too much excess.
This was a good night for me as I got it right for once and there was almost no excess or mess to deal with. This was done last night and it was left overnight to set up.
This evening I started sanding the tail-cone on the inside where the fin-slots are for the internal fillets.
Then I cleaned up the aft of the tailcone from where I ground it off, using some 2000 wet sandpaper. I did this because once I assemble the MMT and fins, sanding the aft end would not be possible. I also made sure that the internal sanding that I had previously done on the aft end was adequate for when I adhere the retainer as the assembly goes together. The plan is to rough up the retainer part that slides under the tail-cone and epoxy it to the tail-cone.
Up next will be more prepping/sanding of the fins using two different grit sand papers, a heavier grit for where the fillets will be and a finer grit just to sand off the shine. I like the shine but I will be clearing the rocket with something possibly just polish, but I want it to be a bit more uniform. Also to sand will be the area on the outside of the tail-cone around the fins, again this is where the fillets will go. I will be marking this off using my carbon paper method. Then I will be onto tacking the root of the fins to the MMT and this fincan may be close to complete, except for fillets. The fillets will be done after I glue the fincan to the booster tube.