The protruding primers absolutely happens with controlled round feed rifles, with ctgs producing less than about 45,000psi.

Ctgs. over that pressure level then usually stretch at the web and re-seat the primer, flattening it excessively in the process. Many see the excessive headspace result as being high pressure, when it is not.

Thus the excessive headspace caused what will become case head separations along the way & usually with the next firing, if the shoulder is shoved back during reloading that case/s.

Case head separations are caused by firing unaltered ctgs. in rifles with excessive headspace, not by excessive pressure.