Hi Lorne, Sometimes the mix you have mentioned can cause a
problem. Most likely your problem is in the spruing area. Don’t
worry about turbulence right now. Spruing is consideration #1.
You should be spruing to the thickest spot (or spots) with a
sprue(s) that are slightly larger in diameter than the spot you
are spruing is thick. Old Silver can give you more firescale
problems, but that is a different story.