I have several FX Crowns in various calibers and configurations, I thought I would give the .177 cal a try and I am using a STX 500mm liner with extended shroud, set up to shoot 10.5gr Crosman Premier heavies just a little over 900 FPS for best accuracy and power and am amazed how accurate his little .177 is.I can consistently print 3/8" groups at 50 yards all day long. I tried to make gun as light and efficient as possible, using a FX 300cc bottle and reg pressure is right at 90 BAR. Getting 100+ shots from a 250 BAR fill Tried several other .177 pellets and none come close to the 10.5 CP's