Last year I took various cartridge components from Colorado to the UK, in my checked luggage. Here is what I had:
1) Unfired cartridge cases where the bullets had been pulled and the propellant removed.
2) Oiled primers (made inert)
3) Intact unfired bullets (as mentioned above, pulled from the cartridge cases) in various calibres.
Here is what happened:
1) On the day before I left Colorado I had a word with the security personnel at Colorado Springs airport. I told them what I was planning to take in my checked baggage. The advice I received was that the US carriers on both legs of my trip back to the UK were happy for me to have those components in my checked baggage as long as there was no loaded ammunition and as long as the components I was transporting did not constitute a hazard to the airplane or the passengers or their belongings. I was warned that the UK authorities might confiscate the items as I arrived in London.
2) I flew from Colorado Springs to Chicago and my luggage was automatically transfered to the intercontinental plane. While I was waiting in the boarding lounge my name was called and I had to go and see security at the gate. He advised me that the components had been found on X-ray and their properties had been identified and that although the carrier was happy to let them on board in checked baggage, I might get these taken away upon arrival in London.
3) Upon arrival in London my bags came through to the carousel with no unusual deviations in handling/announcements.
4) I had nothing to declare financially. I could have just walked out. However, in situations like this it is better to declare what you have in case you have drawn attention to yourself and you are being observed because of a mistake being made in the recognition/ID of the components. So I took my bag to customs and opened it up and said "I have cartridge components here and they may have shown up on X-ray as loaded ammunition, which they are not."
5) The two people at customs had a look at the components and said "Bloody hell, mate, these are big bullets, these look nasty."
6) They could not recognise what components these were and could not tell me right there and then whether they would be taken or not. They called the special firearms cutoms experts and I had to wait for half an hour before they arrived.
7) The firearms guys had a look and basically the problem was this: several bulllets were hollow-points and therefore they are illegal to own because they are classed as expanding ammunition. They told me they would take the whole container and have all the components analysed and then they would notify me by phone within three days whether I could have all the components, some, or none. What was clear was that I was not in trouble with customs as I had declared these first.
8) I had to prove that I had a reasonable need for these items. Luckily I had my manuscript with me (almost finished) to do with gunshot wounds and related research. I provided them with some ID and let them see my research papers and I also provided them with the name and address of the individual who had rendered the primers inert in case they needed to contact him. Then I left, fully expecting to lose all the hollow-point bullets and all the cartridge cases.
9) I got a call the next day saying I could come and fetch the items. I was allowed to keep all of them! I was told something by the firearms expert at customs about the hollow-points, explaining why I got to keep them, but I have decided not to repeat that here because I don't want to aid nefarious dealings to do with these projectiles.
10) I kept the guy's name and number and the evidence tag that they used to seal the items after they examined them. Just in case someone one day asks what I am doing with these.
My opinion about shotgun cartridges: these shouldn't be a problem as long as the cartridges are fired and there is no propellant/primer left. To be extra sure, he could cut the hull once down to the head. I have several shotgun cartridge components here that I shipped in a container from SA and I had no problems at all. My feeling is that France is going to be less anal than the UK about these components, but the key is to declare what you have at both ends of the journey. Just be honest and if they take the stuff away, that's unfortunate.
But if you hide them and they get found....hoooooo booooyyyy