10 percent is actually what I'd expect regarding overlong and overshort (undershort? naw, that's BVDs!) brass. Just finished trimming all my .357s, and will try harder to keep them sorted by number of firings so they all have a greater chance of growing at the same rate.
Otherwise, a crimp die adjusted for the "average" will kill about 10 percent of the motley lot, and will not crimp the short 10 percent at all. On average, FWIW.