I tend to shoot only one arrow at a time when practicing on my McKenzie target. So that arrow gets shot a lot. This summer I suddenly started shooting very poorly, kinda kicking myself, couldn't figure out what was wrong. Checked the brace height of the bow and knocking point, nothing there. Looked at the arrow and could see nothing, rapped it against my leg and could feel no vibration of a cracked shaft. Finially on a whim I put it on my spine tester, what should have been a 65-70lb shaft was only spining 40lb. Bingo! While there was no visual defect, I suspect that pulling that arrow time after time out of that McKenzie had some how broken down the shaft internally. Noticed that if I flexed the shaft one way or the other it would stay there. Took the point off and dicarded that shaft. It was Doug Fir, by the way.