I have noticed lately that my G21C has a problem. When the slide is open and locked, and I slide a magazine in and tap it in, the slide sometimes lets go (closes) without releasing the slide lock. I think it is rounded off. I used to let my mom shoot it and she would release the slide by pushing the slide lock down instead of pulling back on it. She since has bought her own Glock (G19). So can a gunsmith fix this? Help the newbie. Thanks!