The brass "failures" that I've seen are usually cracks appearing in the area of the crimp, or sloppy primer pockets, as previously mentioned. With the lighter loads that you talked about, you may be able to lighten up on the crimp a bit and thus lengthen their lifetime.
I bought 500 Starline brass for heavy-duty .45 Colt...and I still have some brass that hasn't been loaded yet. Of course, some of them have seen a lot of reloading action.
So good brass, as in brand-name, is also important, IMHO.
I personally like Federal, Starline, Hornady if I'm going to buy new brass.
Sonnytoo