To begin with, it’s time to scrap any case when it develops neck splits, regardless of the number of firings it has on it. Each time a case is loaded, the mouth is belled for the next bullet. After the bullet is seated, the neck is crimped to hold the new bullet in place. This constant working of the brass will harden it to the point that it develops splits in this area. This is probably the single most common cause for case loss. It can be reduced by simply working the brass no more than absolutely necessary. Don’t bell the case mouth any more than is needed to get the next bullet started, and don’t apply heavy crimps unless the load actually calls for it.