"Lexan", "Plexiglass" are both trade names.
Lexan is a form of Polycarbonate, Plexiglass is Polymethyl methacrylate, more commonly known as Acrylic.
Depending on where you go, ultimate tensile strength varies slightly - According to Emco, for instance, their Polycarbonate has a slightly lower tensile strength then their acrylic.
Obviously, the ideal way to do it is to use an MQ valve, and huge chamber, so the gun can be run below 200PSI. But that wouldn't have all the nifty moving parts.
The way to still have a moving hammer, and not have it haze up, is to build a new hammer, ideally one with a with a PTFE sleeve on it, for reduced friction, and less wear.