I should contribute to this thread as I'm that "fellow" Tom sourced from. Glad to see his playing with the bits I sent. I pretty much said the same WRT propane's being able to produce the heat but suggested the issue is the small torch set up.

When I braze a crown/steerer (these days nearly only with bronze) with my O/A set up I use a tip with about .060" diameter. I find that tip size (for my Victor J28 this means a #3 tip, for my Purox it's a #15) is about the max I can run with the mid/smaller A tanks I use. I haven't gotten Acetone spitting out... But this made me remember some forum I attended back in 2019 we had much the same discussion about A flow volume WRT tank size (or the surface area of the top of the dissolved A inside the tank). Here's a chart referencing this flow volume VS tank size from, I believe, Smith. Andy.