At this point (if it were mine) I would probably suspect a twisted or otherwise magwell/grip. You can insert the mag into just the frame (slide off) and check clearance of the mag, side to side. I once had a cheapo polymer pistol with that problem.

I hear your frustration with S&W and agree. Sounds like they just tried mags with no rounds, and mags engaged correctly at the factory. Had they duplicated your loading, etc, they might have experienced the same issue.

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