S&W know way more about gun than you ill ever dream of, and they missed it!
They handle thousands of guns a day, they all look the same to them...
You have powers of observations that people don't have power of observations. I'm curious why your curious?
Don't you thoroughly inspect a gun before you buy it? Or least clean and check it out after you get it home? Especially one you're paying $1K+ for?
My Ed Brown 1911 is my most expensive handgun. After spending 20 minutes examining it at the dealer I brought it home and tore it down for a cleaning and thorough inspection. I wanted to see what $2500 looked like inside.
But, I do that with all my guns.
I've even disassembled used guns (when the dealer/seller allowed it) before I bought it.
Maybe I'm just less trusting.
I'll admit, that's not the kind of problem you would expect to see and I'm not trying to insult the OP. Obviously, that's something he didn't notice, as well as a few others after he posted the picture...
Anyway, it will need to go back to S&W for a new cylinder. Maybe he can convince them to let him keep the cylinder as it would make a great conversation piece.
Jim