The first answer
is correct, it is caused by the bullet wobbling and it doesn't hit straight and the paper flips it . The bullet wobbles or goes in a circle called yawing because for whatever reason, slow twist or some other factor it hasn't went to sleep as they say and is not spinning true. I have a .17 Rem that seems to exhibit this on a really hot day with berger bullets. So I use only Hornady bullets in it now. Max