I have a 639 (fixed sight version) that was a duty gun, along with 3 or 4 of the original all-metal 8 round mags. It is one of the most accurate handguns I've ever shot and it's never bobbled. Only thing I've replaced is the recoil spring. The newer -39 mags are indeed 9 round and aren't really flush in the 639 as the floorplate is longer, but they've worked fine. All-in-all, you've got a great gun. Most 3rd gen Smiths are seriously underappreciated. The first-gen 39s, like the Illinois State Police adopted 50 years ago, are beautiful guns. Maybe one of the old ISP guys on here can chime in, but I think they carried 115gr Silvertips in them. It wasn't altogether too uncommon to see an ISP old-timer still carrying a 39 or 439 in the late 90's and early/mid 00's, but I haven't seen one in a duty holster in at least 10-12 years.