Benjamin Kratos.
Mine unmodded runs 400 to 877 FPS with Kings with a simple twist of the power knob.
On low power the Kratos is very quiet. If you adjust your hammer spring to give you 500 FPS at low power, with a twist of the power knob your getting close to 50 FPE on high power.
You have four ways to make it quieter, lower the power and shoot 34 grain pellets, get an 1/2 x 20 adapter for the shroud and use a ldc, remove the entire very effective shroud and use the 1/2x20 threads on the end of the barrel for a ldc, if you want to be very stealthy, build a sound box and use any of these methods with a sound box. The sound box is great for bench shooting and off hand shooting, but unless you hire sherpa’s to carry it, no so good for squirrel hunting.
Regards,
Roachcreek