[John Farrell, Charter Member #33]

What hotshot said. That looks like a classic 2 5/8" hull trying to crimp like a 2 3/4" hull.
Other considerations. What wad are you using? Cut the hull open and collect the shot, remove the wad with a pair of needle nose pliers, remove and weigh the powder. Start over with the reloading process and weigh both the powder charge and the shot. If the powder charge is, say double the recommended weight, the wad will sit higher in the hull and prevent fold crimping.

It is at least one of the above. My first concern would be the powder charge raising the height of the wad in the shell.