So I picked up a used in great condition Sig 229 .40 today from an individual. He said he had no issues with it, just getting out of .40. It was clean, box,docs and 6 mags (3 Sig and 3 aftermarket). I loaded up 2 mags of WWB and it ran great. I ran thru 200 rounds. Came in and cleaned it and loaded up a mag of Fed Prem JHP and cycled the slide and the first round jammed against the feed ramp. Dropped the mag and tried it about 5 more times with same result. I disassembled it, everything looked good and put it back together. Tried it again with the same mag. Same result. Loaded up some more WWB and it was fine. So I tried 2 different mags (1 Sig and 1 aftermarket) with Feds and it was fine. I manually cycled the entire mag twice with no jams. Loaded up the first mag again and it jammed again. Is it safe to assume the mag is faulty? I'll take it out tomorrow and try firing with the other mags with Fed ammo and see what it does but it just makes me a little uneasy since I have no history of the gun.