The Collapsed Shoulder is in an old Speer manual. Light loads & slow powder are the cause. Use a faster burn rate of powder. Pressure is low & neck not expanding to seal. Make sure the bullets have enough neck tension. The expander (if using one) should be .002" smaller than bullet diameter. This will keep the bullet from moving when the primer fires. The bullets bearing surface should be in full contact with the neck. If seating the bullet long to get close to the lands/rifling there may not be enough shank of the bullet in the case neck. http://thefiringline.com/forums/showthread.php?p=4928827#post4928827