Can't tell fron the outside, but I know better. Somehow this joint got contaminated, or something. The brass didn't flow all the way around like it's supposed to when you tin. Tinning is when you going around the joint and flow brass around the joint, sealing/penetrating it and creating the internal fillet. If the brass doesn't flow on the outside, it probably didn't flow in the inside...Probably. But I went ahead and built my fillet in hopes the second pass would correct the problem. There was no direct evidence of this, so what do you do? I mean it could go either way, but just to be safe a sawed it apart. All that work, time and $150+ of tubing and material down the drain.
Well it turns out I was right, it lacks an internal fillet in the place where I suspect I would find one.
To give you a better picture I sawed it in half again to give you a cut away view. The internal fillet doesn't have to be big, it's just got to be there to anchor eveything together.
What now? I can't get discouraged. I just got to emulate PhilWood oil...Tenacious.