Thank you , but I am looking for the detailed differences from the standard 686 and this version.
From web results that the "security special" is a customized 686 (CS-3?) but I would like to know the list of the improvements.
From the web: "After the CS-1 production run (both for Customs Service and over-run guns shipped to US distribution), the factory left this model in the "line" for future law enforcement orders. Think of the CS-3 as simply the same model as the CS-1 but a later engineering change. The basic CS-1 features are there - bead blast finish, round butt gripframe on both 3" and 4" models, and a pinned in front sight. The CS-3 also has the later - CNC machined - ejector star that appears to be a square cut (due to the CNC machining), as well - the front sight is wider - 1/8" instead of the CS-1 model's 1/10" wide blade.
Many CS-3 guns were shipped into US distribution, but the majority that I've seen were actually shipped to S&W's German distributor - Wischo - and marked on the sideplate as ".357 Security Special". These guns were 3" guns. They were apparently slow sellers and many were returned by Wischo and released into US distribution".