Scout, you are right about the taper crimp. Don't roll crimp for rimless cases. In theory, it will headspace on the case mouth. In reality, due to variances of brass length in manufacturing and manufacturers, it headspaces off the extractor. If you were to roll crimp, you likely would not be able to chamber the round due to a slight bulge at the crimp. Your dies will adjust to allow you to apply the correct taper crimp.