[John Sabato]

Matching Part #'s even in a Krieghoff doesn't guarantee smoothness. Does the breechblock travel smoothely in the upper receiver if the sear is removed? Or does it bind anywhere? Be generous with gun oil in those grooves. Does the stripped upper receiver travel easily in the frame? Any problem with ejection with or without a magazine iinserted? Try removing the left grip. The interior of the grip may be rubbing on the mag button wth just enough drag to slow down the follower so it misses the feed timing cycle causing a failure to feed.