The 5.5 New Model SBH all come with the fluted cylinder. All other SBH come with the solid cylinder. Why, I don't know. Maybe to add some weight to negate recoil. Maybe for looks. They do not add anything to strength, the thinnest part of the cylinder is between the chamber and the locking notch. Look at the chamber under the notch, and you'll be surprised at how little metal there is. BTW my favorite SBH is a light-weight I made up. I started with a 5.5 ss ( for the fluted cylinder ), had it shortened to 4 5/8, removed the "warning" on the barrel, and replaced grip housing and ejector rod housing with polished aluminum pieces from blue blackhawk. If I could only own one handgun, that would be it. Mark.