Mild roll crimp. As I have written in other threads, I have recovered a few of these fired rounds from clay banks and found no damage to the plating that appears related to the crimp. One of these days, I will try to take and post some decent photos to illustrate.
I'm not a bullseye shooter, so I'll never be able to tell you the difference between a load capable of 2" versus 4" at 50 yards... I can't produce either of those with a laser gun, much less something with recoil and mechanical limitations! But I have yet to notice any problems arising from putting a mild roll-crimp on the xtreme .41's... nor, for that matter, on their 158 gr SWC .357's. I am not trying to drive either at real magnum velocities, though.