Even a Sigma should not experience a FTF simply because it's being limp- wristed, but FTFs will definitely show up for somebody who's limp- wristing first.
I think the problem actually *is* the gun, but it's probably easily fixed.
You're going to have to strip down the slide and remove the extractor. Inspect the extractor and spring for damage (you probably won't see anything wrong). Thoroughly clean the extractor/ spring, and the channel in the slide as well as the spring pocket. When you reassemble it, don't use any lube in that area.
Afterwards, have your dad try it again. Odds are it won't stovepipe on him anymore.
*edit* whoops! I should read the entire thread before responding...
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