Hatsan mod 55 s power loss

[RichardK]

http://www.hatsan.com.tr/en_mod_55s.html

It was given to me, but looks unfired. Took apart and no broken pieces (as far as I can tell)
The spring inside is "loose" as in it moves around when not cocked, but when cocked doesn't move at all.
Shot a rat in the chicken coop and the thing just did a backflip and ran away, lol. So tried to put it thru a half inch ply and made a dent but definitely didn't go thru. Any ideas?

 

[Barfman]

The spring shouldn't be moving when not cocked. You can either shim it, or get a new spring.

I've killed rats with a pistol doing as little as 360 fps in .177, so it definitely shouldn't be surviving a decent rifle shot.