I've had my 550B for a couple months now, and have loaded just shy of 3,000 .38 cowboy loads.  In the begining, I was pretty disappointed with the crimp that the shells were getting.  I could just never get the neck of the casing to crimp in enough to not hang up in the chamber of my lever gun, no mater what depth I set the crimp die.  I tried several different bullets in both .357 and .358 with an assortment of crimp groove profiles.  Nothing worked. 

My troubles are over, now.  I have been using a Lee "Factory Crimp" die for the last 500 or so rounds, and the shells feed flawlessly. 

Despite assurances from Dillon, I am still convinced that I have a taper crimp die, not a roll crimp die.  I don't have enough experience with reloading to effectivly debate the issue, but more than a dozen folks at a recent cowboy shoot inspected some of my older shells and their opinions were unanimous:  The shells definitly did not have a roll crimp.

Now that I've vented, I feel better.  I'm likely going to send the questionable die back to Dillon and let them have a look at it.  They HAVE been very communicative and helpful as I stumble my way into reloading.