I just wanted to add my positive experience with Jel-Flux from
Pro-Craft and AS hard solder. This flux works better for me than any
other flux I've tried. I'm getting full or near full flow with little
or no skull. I think it may be worth a try if anyone else has had
difficulty getting the AS hard solder to flow. I'm using a Smith
oxy/air torch with a large-ish flame heating the work and then
sweeping the flame back and forth along the seam with palions in
place from the start.
I had been very frustrated with the hard solder until now.