My first reaction to your post was that 100 - 150 yards is a big ask for an Accu (CFX) You might prove me wrong but maybe not.
Stick with it and get it sorted. It will be worth the labour.
Well Im on about shot 180 and this thing has been dieseling/detonation since shot 40-50. It will settle down and then start back up and pop and smoke for 5 or 6 shots every 20 shots or so. Like i read, these thing must be greased to the max! Theres no way this is good for the piston seal. *(&^ Gamo would save thousands if they would learn to lube these things the right way!