Thanks guys! It was definitely not as late as 1993. My only problem is proving any of this, since my father passed away a decade ago. The transfer was "Son, you'll put this to better use than I will. It's yours." He was getting into his 80s and I think he was worried he'd shoot his nose off. I should probably establish the manufacture date from the serial number. I've not been at all inspired to register it. It's reassuring to know I'm not committing a felony. [If I commit them, I prefer not to do it accidentally.
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On the traveling out of state question, I have other pre-ban hi cap magazines for other handguns (P226, P229, etc). Can I assume that the same rule applies? I own them legally, having bought them pre-ban. Can pack them in checked baggage, go out of state and come back without it being considered importing?