> we were able to smuggle old, old artillery shells potato mashers (no wooden handle), and other types of grenades in our checked luggage (plane belly)

If you travel on the Eurostar train from Paris to London...... before boarding at Gare du Nord station you will pass a French bloke by the escalators employed to hold a placard with a sign in English saying not to take unexploded ordnance on the train.

This is because a few years back, some fuckwit did just that, shutting down the channel tunnel for several hours.

https://www.bbc.co.uk/news/world-europe-32690320