You can also leave the selector switch, the plastic U shaped bit, out. Your cut-off lever will fail, this is just how M14s are, and Guarder makes a steel version for those. The best life span I have heard on stock parts is 20000 on a TM cut-off lever. If you want 400FPS I'd go for a POM piston head and check your shimming and lube. There is no problem to having a reliable gun at 400FPS it just wont last as long as if you had a low FPS. Thats one of the reasons why TMs last so long, they don't shoot over 300FPS.
http://extreme-fire.com/SW-COMPUTER.html
semi-semi-safe plus they will soon have pre-cocking which will be available as an upgrade for their MOSFET. I have two of these and they are pretty fun. The AEG boots once its plugged up to a battery.