The answer would just be a generalization. Upon examining the internals of S&W's from the perspective of a machinist and a person with a degree in Metal Processing, the inside of the revolver (without regard to stainless or Carbon Steel), exits the factory with no apparent finishing of the friction points other than sear/trigger surfaces. Machining marks still exist as produced. Therefore, there will be a great variations in trigger pull between two instances of the same models made of the same type of steel, let alone one of Stainless Steel vs. one of Carbon Steel.Carbon steel S&W always smoother action and trigger than stainless?
I agree with your assessment as to MIM parts, but the S&W frames (under the rebound slide, around the hammer pivot, etc.), are forged, then machined.Many of the machining problems that folks paid to have pistolsmiths smooth out have gone away with the use of MIM parts. Since MIM parts are not machined, there are no tool marks that need stoning for smoothness.