I went through 3 of the 5 pages and have trouble understanding what went wrong so bad that discouraged continuation? Can someone summarize? Feel free to PM if not desiring to post publicly. I built a Dominator 4 v1 with a boat tail retainer and indeed it was a devil.
I tried and succeeded in getting the centering rings just right so the fin tabs ultimately abutted against them while maintaining the proper
overhang of the aft end of the mmt. Some pictures on a Dominator 4 I was going to use for an L3 attempt but decided against it because I
didn't feel I had enough room in the upper bay for an appropriate parachute. Plus I was going to use two Featherweight magnetic switches.
The upper bay is flush mounted to the sustainer with a thrust ring in the forward sustainer to take the loads. Room for a chute is at a premium and I was too far along to redo the upper bay or buy a longer upper bay body tube. It will fly but not as an L3 attempt rocket.
Getting everything lined up when epoxying the mmt assembly in the rocket is challenging to get the right overhang
of the mmt out the aft end and still have the forward centering ring just line up with the forward start of the slot. I didn't mount the aft ring until internal fillets were laid with a silicone tube swaged to a syringe to inject the 4525. I used Duralco 4525IP epoxy and it works for the fillet material as shown too. The one view is of the McMaster Carr metal jacknuts that are great for glass rockets and mounting the rail buttons. I used a bit of plywood for a standoff.
In the motor mount end, I had to drill the hole for the jack nut all the way through the motor mount tube, inserted the jacknut and screwed it down. The jacknut retracted to the outer wall on the aft rail button and all is fine there. I had done that on a 4" Wildman Rocket previously so no sweat there. (I'm going to use it for the L3 attempt as it's more conventional albeit with a longer upper bay tube.).
In the end, I had to sand just a wee bit of the aft end of the motor mount tube in order to be able to screw the retainer flush with the end of the rocket. It was close so I didn't have to do much sanding.
I really sympathize with the poster if the retainer was a hangup as it is pretty involved especially if doing it for the first time. I was building this project over several years and thought long and hard on trying to pull it off. The thing left is to J&B the threaded retainer portion and work on the dreaded electronics sled. I went back to planning the attempt with a 4" Wildman as it is stock except for a longer upper bay tube to carry a larger main chute.
Why the two rockets? Both were on like $200.00 specials years ago and I couldn't resist. I've got two 7.5" Smok'in
rockets "collection of parts" for an Honest John and Nike Smoke that were on special 2 for 1 I bit at too. Those have to wait. Kurt