Did a quick search but coudn't find something similar to my problem. Am using a Coharie MP5K/40. changed bolt, ejector, extractor,trigger group to HK german. using RCM as bolt carrier. problem arises after firing a few rounds. extractor spring tilts out of the extractor until it loosens. tried installing it again and after a few rounds it tilts again until it loosens. extractor spring is new bought from hkparts.net. Installed an hk rifle extractor spring but bolt won't go into battery when chambering a round. I analyzed that extractor was too stiff to move. has anyone experienced this type of problem. thanks.