Start at the beginning. Pull the gun apart and check the fit of the bolt an ALL the cylinder notches. Fit the bolt if necessary. Polish the sides of the bolt, and the bottom of the bolt where it interfaces with the spring. Check the contact surface on the spring. Polish the contact surface flat. Test. When you reassemble, insure the bolt leg of the spring does NOT drag on the side of the frame.
While apart, you should also check the travel of the bolt thru the window. Polish the sides of the window.
Make sure there are no burrs on the hammer cam to interfere with the bolt leg. Polish the contact area of the bolt leg.
Head for the range and see if you resolved the issue.
Coffinmaker