I took my mg 42 semi auto build out to test fire today and had a round fire while extracting / ejecting. The mg 42 extractor holds the case tightly untill the bolt is all the way back when the ejector extension hits the buffer and knocks the case down and out of the gun. A live round was in the bolt when I retracted the bolt and the firing pin hit the buffer ignighting the round. There was a pop and smoke came out of the receiver. I found the case and bullet in the receiver along with most of the unburned powder. it seems that as soon as the case popped the powder went out. nothing was damaged except the case.