I under stand that you have a guy working on casting technique for valves??? Have you ever considered high grade ceramics like those used by Boker Knives and like the ones Toyota used to build working engines from? High end ceramics can be made almost as hard and well wearing as a diamond. The only down side is that they are brittle if droped but how often do valves on high end trumpets get droped. Ceraics are easy to work with and easy to cast and machine. They wear better then steel in many case's. I have considered useing a multi-axis milling machine and high end steel and sumple machine the valves on a lathe and multi-axis milling machine. It would be easy to do since you wouldnot need to make and form air port's that are brazed in like on conventional valves. As for casting steel the bigest trick is makeing sure the temp. at the pour point is the same as it was at the Copala. If the steel turns orange before it is poured then it will not turn out well. Transducers can be used on the outside of the mold to help get ride of pocket's but you need to have an area at the top of the mold that is like an empty cavity that will need to be trimed later. This empty cavity gives the air a place to go. Ihad to fix some issues with GM's brakes a few years ago and it was foundry related. I would also suggest thatyou have a look at investment casting. The initial cost is higher but it will produce parts that are very easy to make uniform and it will elimanate any possable chance for air bubles. Invest ment casting is used to make carberator bodies and gun part's like recievers and bolt's asin bolt action not as in retainers. It isnot as strong as forgeing but itis a lot less energy intensive. If machine cost's are an issue with multi-axis cutting of high grade steel then use copper or bronze and then plate the part with nickle silver. You can remove excessive material from it to lighten after the initial machine of the ports is done. Just some idea's from someone that has been heavily involved with manufactureing in the auto industry and a little bit in the aviation industry.