Master gunsmith Jerry Kuhnhausen and author of the Kuhnhausen Shop Manuals on gunsmithing thought the Mark III and later Colt's were the strongest medium frame DA revolvers ever made.
He attributed this to the frame design and Colt's high quality steel forgings.
The internal parts are made of an early type of powdered metal technology called "sintered steel".
Colt did this right and these parts gave almost no trouble. I saw virtually no parts broken by normal use, EXCEPT, there is some occasional history of the trigger in the Mark III breaking through the pin hole.
This is not common at all, but it was known to happen.
In the later Mark V and King Cobra the hammer and trigger were made of cast steel so even that potential issue was eliminated.
Most modern revolvers cannot be tuned in the same manner as the old Colt's and S&W's could be up until S&W started using MIM powdered parts.
In the Mark III the internal parts were surfaced hardened and if you stoned or polished much you could break through the hard surface, exposing soft inner steel. That ruined the part.
In any case, the Colt sintered steel parts were already so smooth you gain nothing by any polishing (actually smoothing, not polishing to a mirror shine).
The purpose of polishing or stoning was to reduce rough machine marks that cause rough operation.
Since the sintered steel parts are not machined, there ARE no machine marks and the parts are as smooth as will do any good.
For that reason, like most all modern revolvers, trigger work involves installation of spring kits and using a little grease on key areas.
