On a classic DA Colt like the Python, the cylinder latches into the frame at the rear of the cylinder only. Out at the crane, it can "wiggle back and forth", so the alignment of the back of the barrel to the cylinder bore is a bit iffy under recoil. Only the crane's stiffness holds that end straight, but that's at the end of a couple inches of metal bar (the crane).
To make up the difference, Colt heat-treated the crane better. On their best guns of that type, such as the Python, it wasn't too much of an issue. On "lesser stuff" like the Dick Special, Police Positive or similar, it was a bit more troublesome as a long-term thing.
On your average S&W, there's still no lockup "right at the crane". The very tip of the ejector rod is dished and "plugs into" a spring-loaded button under the barrel, so that end of the ejector rod is "loosely locked". But as the ejector rod is skinny and can wiggle, the increased "cylinder stiffness under fire" over a Colt is marginal.
Like the Colt, the S&W locks at the rear.
Ruger and then DW and Charter Arms came up with a latch that locks the crane solidly into the frame, in addition to the latch at the rear. With the cylinder "axle" held stiffly at each end in the frame, both accuracy and reliably are at least theoretically improved.
S&W played with a crane lock briefly, while retaining the "semi lock" at the end of the ejector rod. That was known as the "triple lock". Ruger, DW and Charter all realized that the latch at the end of the ejector rod was of limited usefulness, so they either let the ejector rod free-float (early Charter) or enclosed it in a shroud but otherwise didn't retain it (late Charter, Ruger DAs, Dan Wessons.
Ruger, DW and Charter all rigged up "interlinks" allowing release of both locks (each end of the cylinder) with one button. On Rugers, the release switch is at the rear, DW mounts theirs on the cranes, early Charters had TWO releases (crane and S&W-style button) that were linked to each other. The forward "switch" (actually pulling the ejector rod forward) was deleted on later versions but it's still locking up at both ends.
When Taurus played with two locks on their "Raging" series, they were too stupid to rig up an interlink so they ran two switches, one for each lock. It's got both a DW style crane-switch and an S&W style switch. You have to manipulate both switches at once to swing the cylinder out; OK on a hunting gun but sucky on a defensive piece
. (This may actually be marketing; if people are activating both switches, they'll KNOW there's two locks, and think it's an advantage over, say, a Ruger SRH 454. Wrong. The Ruger has two locks too, but their engineers weren't smokin' something funky when they did their thing.)
On any DA Ruger, swing the cylinder out and push on the back of the cylinder axle pin from the rear while looking at the crane. You'll see a little switch move back and forth at the crane, which fits into a cutout in the frame to match. That's the forward latchwork and you're also seeing how the interlink works.
On a Charter, the ejector pin is "oversize" and backs into a cutout hole in the crane, freezing crane motion during firing.
I haven't examined the DW lockwork but I know it's functionally equivelent to the Ruger except for the funky switch position.
