Same as in non-progressive loading. I sold my Dillon progressive loader because it caused me to not examine cases as closely as I did on the single stage press. Every time you pick up a case the natural thing is to look at it. With the Dillon, I tended to dump the cases in the tumbler and then load with little time spent in actually looking over the cases. I started finding neck cracks in loaded rounds and also discovered I had loaded some rounds that still had media inside that resulted in squibb loads. Just me I guess, but the point is (in centerfire rifle cases at least) in my opinion, case dimension makes a difference no matter how you load.
