It was not, at the time TSA found it, a weapon; at least not how it was described. So why are folks calling it that. It was demilled, they only way it could reasonably be used as a weapon would be to club someone with it or drop it onto someone from a height. It was being brought to the SHOT show, it was declared (source) to the airline which allegedly did not report it to TSA (and why would they). It was confirmed as being a prop that could not fire. The guy with it had the paperwork for it. The guy was released; yet, his so called weapon was not allowed onto the flight by TSA. My bet is a hungry lawyer will make a nice tort claim for him against TSA if that is what he wants.
A bit more in this article: https://www.foxnews.com/us/tsa-finds-undeclared-84-mm-caliber-weapon-checked-luggage-texas-airport
A bit more in this article: https://www.foxnews.com/us/tsa-finds-undeclared-84-mm-caliber-weapon-checked-luggage-texas-airport