That is a unfluted cylinder. Most people think unfluted cylinders are safer as they will take
an excessive hot charge, don't know if that's true or not. Nice looking gun

For a .357 magnum, an unfluted cylinder is really just extra weight. On a fluted cylinder, the grooves aka flutes are offset so the amount of metal surrounding the chamber is quite substantial. Even the S@W 500 mag. revolvers have fluted cylinders, and they can fire a 500 grain bullet with overs 2,000 ft/lbs. of energy at the muzzle! By comparison, a 200 grain .357 round, puts out less than 600 ft/lbs. at the muzzle. Ruger's Super Redhawk .454 Casull has an unfluted cylinder and is known as being built like a tank, so maybe over years of shooting heavy loads unfluted "might" make a difference, I hate to second guess Bill Ruger . Some handloaders might prefer unfluted, maybe someone will chime in on that. Anyway, like I said, beautiful gun you got there!
Eli