I really hug the shelf with my hand and have had this happen before to me, the fletchings (not sure if it was the cock feather, I wouldnt imagine so) was actually cutting my knuckle open just like as if I was shooting off my hand. anyway it happened when I was switching arrows and it turned out the new arrows needed to be knocked quite a bit higher than the previous ones to fly straight, once I did that the problem with the fletchings went away. I think the arrow might have actually been striking the shelf in some way not sure what the actual problem was though. hope that helps some