After really having a chance to look closely at both the 5 and 10 round mags. The 10 round seems to have too much material removed just below the latch groove. The 5 round has a longer flat spot that locks it in tight to the mag well and prevents it from moving back and forth. . This same area on the 10 round, does not have such a long flat area, thus allowing the 10 round mag to rock back and forth in the mag well. It just looks like a manufacturer oversight. I will just see if I can send it back for a trade on a 5 round for an extra..