I have a lot of 10 rd mags: about a dozen Pro Mag, some John Masen, a few clones from CDNN and 3 from Ruger (the first ones I bought after getting my 581 Ranch). To be honest, the only ones that were a problem were the Rugers - had to file the latching lug and drill out the locating pin hole on all three to get them so they could be properly inserted in the magwell. All the rest were (and continue to be) totally functional from the start. YMMVI have a bunch of Pro Mags and I have had no trouble with them at all. In fact,I can tell no difference between them and my Ruger 10 rnd. mag. except they don't have the Ruger logo,that's all.