If you send a gun into the PC shop for a Master Action Job it will return with the ribbed Wolf spring installed. Possible that some new PC guns are coming so equipped. I don't know. On the MAJ I believe a longer main spring screw is fitted to insure reliable ignition. I've had a few done and this is how they were returned. Zero ignition problems and a nice smooth action. I don't know if the Wolf spring is utilized on the other action jobs offered by the PC shop. I keep the standard OEM springs, both rebound and main, in all of my other guns.