Bad brass or overcharged. Thats a wild case rupture. The 40cal is one round where you have to be careful on bullet depth. Pressures can shoot up. Maybe somehow the bullet got knocked in the case further.

Also, if your gun has a rough feed ramp, or jams easily, it could have pushed the bullet in the case further. I have a 357sig and had this problem. I had to have the feed ramp smoothed out.