I used to machine parts for a aerospace/military manufacturer out of AlBeMet which was 70% pure beryllium and 30% pure aluminum. Shit was crazy expensive, super lightweight, super rigid and really really tough to machine. It was all done with ceramic tools or CBN inserted or diamond coated carbide tooling. Some of the coolest stuff I ever did and only thing worse to machine was a nickel and tungsten infused aluminum that we made large bearings for under ground mining equipment out of but that material was almost as heavy as solid carbide.
Can't believe anyone would be making beryllium pistons, that shit is extremely toxic! I had to go through special training and wear a breathing apparatus when I machined it even with a full enclosed machine. Then had to be tested every 6 months for lung issues.