When I first bought my P89, I went shooting with a friend that had a Ruger P94 and we commented on the magazines looked identical. Well, we swapped magazines and I discoved that his P94 mag worked just fine in my P89. That was great because a 10 shot P94 mag holds 12 9mm's. Well, later, when the high capacity ban was lifted, I bought a 30 round magazine for the P89.
Fast forward to today, and I have a PC4 carbine. I was disappointed to find that it does not function properly with anything besides factory Ruger magazines, and it will jam with the 30 round P89 mag, or just about any other 9mm magazine I put in it. So, to answer Plink's question, if it isn't made by Ruger itself, it's not likely to work.