You've got a dirty shaft. There's a metal bushing that runs through the playfield and contains a shaft that's attached to the gun and makes it rotate. The bushing gets dirt inside it and makes the gun drag. Take your gun apart and clean the bushing and the shaft. And yes, the shaft does pull out through the top. If it's as gunked as the last one I did, it may take 20 minutes and a lot of swearing to pull it out.
New! Dark mode!
Browsing Pinside at night? Getting tired of all the white? Switch to dark mode using the button in the top right (or CTRL-B)!