I had one FWB 124 that i absolutely couldn't get the piston out! Some idiot had peened a dimple in the tube between the trigger and the disassembly bolt!

That dimple even made it a chore to get the trigger unit out,.....

......i had to back off the compressor a few MM's and use a wooden dowel and hammer to tap on the disassembly bolt,....tap tap tap,....then back out the compressor a few more MM's.

Eventually i got the trigger unit free, but the piston wouldn't clear the compression tube with the dimple still there. So i used my jeweler's flexable shaft machine and a small drum sander to remove it.

.....came out fine after that! lol

.....i ended up putting in a Maccari "Everest" full power kit and seal,......shoots hard and sweet now........

......hope that airgun mechanic retired! lol