First I would take the mags apart and clean them well. Make sure the spring and follower move smoothly. Inspect the feed lips for any burrs, bends, etc.
What is the history of this gun - how long have you had it, how many rounds have you put through it, have you done any other modifications to it, has it always had this problem? What is your level of shooting experience? If you are relatively new to shooting, sometimes limp-wristing can cause jams. Let someone else with more shooting experience shoot it and see if it does the same thing to them.
Look into these things, then send it to Ruger if you don't discover the problem. I can't recall if this will void the warranty or not but just to be safe, I wouldn't mention "reloads" to Ruger.
