I bought a 4566 police trade in 3 months ago. Etched on the right side of the dust cover is H.P.D.553. Whatever PD that is. Absolutely a great gun, I treated it to a new Wolf firing pin spring and a Wolf factory spec recoil spring just as a precaution and Hogue black rubber grips to replace the same grips that were on the gun but had some wear. Fit me very well. I have fired about 350-400 rounds through it consisiting of 45 hardball, Remington 230 grain Golden Saber, Hornady 200 grain XTP and Winchester 230 grain JHP. All fed without a flaw. It shoots where I point it! It is now the gun I carry in my truck consul and in a Missouri winter ocassionally concealed as I have a Missouri CCW permit. Probably couldn't carry it concealed in the summer. Even when I carry my snubby 38 on my person the 4566 again is in my truck. My carry load is Remington factory 230 grain Golden Saber. Since I am a reloader I load practice ammo with the same bullet. I really like this gun!! I wish I had found S&W 3rd gen pistols before this! Got an El Paso Saddlery Double Agent holster for it. A little pricey but great leather.
The Wolff spring kit did fine. However I did find that the firing pin spring took some pressure to fit together as did the recoil spring. When I laid them out together the recoil spring in the pistol was 1/2 inch shorter. I believe it had taken a set. and it was DEFINITELY harder to reassemble the psitol with the new spring. Again the old spring had probably taken a set. Function is flawless however.