Next I kludged up a long BT-50 to ST-115 centering ring. I cut another short piece of ST-115 and cut out a strip to make it a slip fit into the body tube; then I added three layers of 90# index cardstock. Here it’s glued up, dry fit inside the end of my leftover ST-115 to keep it round. Once that was done I glued it onto a piece of BT-50 and then glued that into the front end of the airframe. There’s more to be done on the front end but it’s time to take care of the back first. I printed out my cone template from OpenRocket, twice, on cardstock and cut both out. Two because I’m making a double layer cone. I omitted the gluing tab. There needs to be a slot for the launch lug, and it needs to be in different positions on the two pieces so I can offset the cone seams. I’m not sure exactly how long the slots should be but I used OpenRocket to make an educated guess.I cut the slots out, but not all the way to the front edge, for now at least.
Then I made the cones. I used bond paper tabs on the inside surfaces, so the seams are butted rather than overlapping. Meanwhile I also made an ST-7 to BT-80 centering ring by the expedient of gluing an ST-7 to ST-115 ring onto a BT-50 to BT-80 ring. I cut a notch for motor hook clearance.
Once the cones were ready I selected the one I liked better and glued the other inside it. I trimmed the part of the inner cone that was sticking out the back. Then I dry fit the cone, motor mount, and big centering ring.
Finally I pulled the cone forward, applied glue on the outside of the body tube just where the front edge of the cone had been, and slid the cone back to place.