Took me a while to find the article, I for the life of me couldn’t remember the name of the company -
http://www.sae.org/technical/papers/970292
I don’t care how precise it is, at that size and weight we could mass produce them if we wanted to.
At 29% efficient, why would we want to mass produce them?
Gas turbine component costs are not really about precision components. You can buy a $5 roller ballbearing with the OD cylindricity within a couple ten-thousandths of an inch.
Gas turbine components need specialized materials developed for high-temperature applications. That means high-nickel super alloys, if you want the engine to last for more than a couple of starts.
If you think gas prices have escalated sharply, you'll really get your feelings hurt when you go to buy some nickel.