James: Thank you. Since I've JB Welded the fins on, I've got a slightly spiky water bottle now (I did keep all cut edges turned in, though). I was thinking that adding a shroud would make it a little smoother to pack and access as a water bottle.
Ben: Re: Extending fins below pot to capture all the hot air. I thought about that, but there's so much length/mass in the fins, I'm thinking a shroud of the current outside diameter is less weight than making all those fins taller. The windscreen I envision is JB Welded onto the outside of the heat fins. But maybe it could be beer-can thickness instead of flashing thickness.
Ben: Re: JB Weld's thermal conductivity - imperfect compared to lead solder or that Arctic epoxy with silver and aluminum. But I smooshed the fins right to the Rockstar can to achieve contact and the JBW fillets around that contact. I'm sure the JBW is better than air. And I can get it in my little northern town. I also liked the safety margin between 600F rating and 212F boiling. But, yeah, there's probably better stuff. Certainly JBW's chemistry but with silver instead of steel would be better.
Clayton: "What's stopping you from welding the fins to some kind of windscreen? If you kept the ring tight enough that you had good contact with the Rockstar can," I'm not sure if this is what you mean, but your post has me thinking: if I welded the fins ONLY to an outer windscreen and NOT to the Rockstar can, then I could separate them, pack them each more tightly (a la MSR's version), and retain the water-bottle function of the Rockstar can.
Clayton: Re: the jig. I'll get some pics of that in action and post it. I started bending the flashing by hand and it wasn't straight or consistent enough at all. I wanted all those inner turns to touch the can so I need a pretty consistent procedure. A hunk of scrap plywood, some wood glue and a few air-gun brads and I had a jig. Pics coming. I'm now trying to imagine a jig for the Jet-boil style of HX.
And you know what? When I finish these experiments? I might end up with a better BPing pot. Or I might stick with the Jet-boil pots. But I'm sure:
1) I've already learned a lot.
2) I've fun doing it. and
3) I'm going to have the fastest, most efficient pasta pot in town when I convert it with bottom and side HXs and a shroud. Cause in a good year, I BP 20-30 nights. That leaves 300+ nights of cooking dinner at home.