Cylinder question for m27-2 & m27-3

[SWBigBang]

Did they change the cylinder between a 27-2 and 27-3?

Looking at the back of a cylinder of a 27-2 there are groove so the rims of the .357 fit.

Looking at the back of a cylinder of a 27-3 it is all flush.

Was this a design change and typical of a 27-3?

 

[mtime7]

thats where they deleated the recessed cylanders,, they also deleated the pinned barrel