Standard 4506's or 4566/63 tsw models dont come with a spring loaded decocker or a bobbed hammer.Some melonite 4566's had spring loaded dc's,and 4513tsw had bobbed hammers. So Im not sure what model your dealing with unless it is some type of special order,only the PC guns came with a briley type bushing unless, someone sent the gun in for some special work, of course with SW there is always the possibility of a special run of something,so maybe thats it,a spring loaded D/C is easily changed out for a regular version, good luck, /Bob