I have a 2010 production C3 and its never failed in any respect in 2k ish rounds. I did, however, buy Chip McCormick mags from the get go and never used the factory as it sits flush and tends to pinch my palm. Sure sounds like a mag problem to me. I would recomend trying any of the above mentioned brands before I would send the gun back to Sig.
How about some pics? I've never seen a C3P.