My duty gun in 1990 was a 4506 with the square trigger guard(my own). I liked it so much I bought a 5906. The 4506 started having light firing pin strikes and I took it to the S&W warranty center. They "fixed it" and told me they could not test fire it. I took it out and click it went. I thought I didn't put a round in the chamber, pulled the slide back and out it came. Tried again and click. They had to send it back to Mass and then it sat in limbo while they argued over who would pay for it. I lost faith in it an sold it when I got it back. I did keep the 5906 and carried it for a couple of years, still have that one.