Looks like I need to put baffles in the tube. I will use the distancing of the original Unitron F15 tubes. Any suggestions on how to make the baffles?
When I redid the baffle in the 80mm f15 Jaegers, I used the technique of mounting the rings on thin dowels and sliding the whole assembly into the tube. The rings were made from thin plywood, like you can get at craft and hobby shops. The smaller holes were cut with a hole saw. For the largest, I drilled a series of holes, then carefully cut between them with a razor blade. Lined them all up and drilled three holes through all of them, near the edge, for the dowels, then glued it up with the proper spacing. It ended up a tiny bit warped, which gave it enough tension in the tube to stay in place.
For the 6"f9, I'm planning to add some baffles this spring. It only came with two in the middle, each about 1/4" thick, doing double duty as baffles and reinforcement of the tube against pressure from the rings.
I have some 1/16" aluminum sheet, and plan to cut the holes with a fly cutter. At this point, I think I will cut the outside circumference with the bandsaw. I could directly glue them in place with JB Weld. But have been playing with the idea of making three small tabs on each, that bend at 90*. I would over-bend them in a bit for test fitting, then bend them out a bit to provide a little pressure for final placement. A dab of silicone glue under each would hold them. What I like about this is that if the rings are a hair under-sized, they will still have some mechanical force keeping them in place, and the tabs can flex with expansion and contraction. It would also be fairly easy to reverse.
For the Jaegers, there was no way to reach into the tube. The 6" has a 7" tube, so it's easy to get into. A 4" tube would be a close call for one way or the other.