After a month of backorder I just received a mag for my Ruger mk I from Triple K. Haven't had a chance to take it to the range yet but it appears to be constructed like the original factory mag, with the zig zag spring and fixed bottom plate. Only noticeable difference is the bottom plate is black plastic instead of chrome steel but it does load & drop just like the original mag. It's also the same width as original, unlike the current Ruger replacement mags. The button for the follower also reverses if needed. I've run Triple k mags in my High Standard Sport King for years with no issues, so i was willing to take a chance on this.