So I go to remove the burner and no-go. Turns out the exit has belled, pretty wild. Also disintegrating.
It's about an 1 1/2" to long, .8125 id X 8.75 running a .031 tip. I do have the inlet beveled.
With the 2 burners, it would melt a #2 crucible of copper in 20-30 minutes.
Volume is about 990 in3, 10w. X 9h. X 14d. I used 9.5 for the dia.
The volume will reduce a little as I plan to line it with the cast refractory and still use the same depth of blanket, 2".