You might look at Kelly's lance. He came up with a great way to make fine holes, and small bubbles is what you want. I was melting some dirty scrap making ingots yesterday and I was getting 11 minute cycle time pour to pour. My crucible is small, I was pouring 5 lbs at a time. I'm using a 4-1/2" OD 304 stainless steel pipe for a crucible and have a couple of hundred pours on it. I'll make another when necessary for aluminum. In what I do, and your parts so far, all I see with casting alloy is a slight improvement in surface finish. What are you burning for fuel?