[Peter M. Eick]

I think WalterGAII has the right explaination. The factory crimp die does not resize every round, it only knocks back any rounds that are slightly "off".

I see it do the most effect on my 38 special rounds and the 380 auto rounds. he problem with the 38 special is that the brass length varies a bit (some are short and some are right at the max trim length) so the roll crimp will some times raise a bulge that hinders clean insertion. The FC die resizes that bulge and all is great. I do not even have to use the crimp part, just getting the first 1/4" of the brass into the die does the trick. The same is true for my 380 rounds (such is life of range brass).

If the die does not size your rounds at all, then you are correct and you are only crimping, but if you are using a meddle of brass from different sources, you may need it.

ps: I am looking forward to the day that all of my mixed brass fails and I am only using Starline. But until then, I cannot just throw out good brass!