Dyotat100
I thought my 35 cal Jkhan N400 ( 150 fpe) might be acceptable, I ended converting it to a 30 cal ( 100 fpe) Pellet shooting rifle.
I might consider building a regulated (200 bar) dump valve air rifle, electronic trigger, no hammer, press buttons to charge dump chamber . No 90 degrees air flow bends, should be able to produce 400 - 450 fpe.