Bought a 300 wm mod 70 XTR push feed (1986 year) used and put a 26 in shilen barrel on it with my gunsmith cutting the chamber. Problem is sometimes it extracts the case and and more often then not it doesn't. Cycle speed seems to make no difference. I have taken apart and cleaned the plunger, spring and extractor and plunger hole plus polished the extractor to no avail. Can order parts from Jack First in Rapid. Am I on the right track or should I be looking at something else causing the problem'? I have had mod 70 push feeds in the past and never had this problem.