Brass life depends mostly on how hot you're going to load them. With max (or near max) loads, you might get 5 - 6 reloads before they start to go. With a fairly mild target load, perhaps two to three times that. You need to be sure you're not excessively resizing them, and annealing the necks when needed. I think keeping brass clean by tumbling can also help with life.
In most cases, it's split necks from either not annealing or improper annealing that ends the life of a brass case early. The other problem is expanded primer pockets from hot loads, or even case head separations.
And finally, I guess a badly cut chamber will also contribute to short case life.
