Returning from the ECRA meeting in Germany, one of those attending tried to carry back about 0.3Kg (0.66 lbs) over his 5Kg weight limit. Remember, the weight limit includes the weight of the boxes. He was flying Lufthansa with a connection in Frankfurt. His bag got on the first flight, but when it was scanned again in Frankfurt (as most bags are at international connections both in Europe and the US) it was found to weigh 5.3Kg and was seized. He had some great items from the meeting, and his cartridges were very nearly destroyed. He got lucky and made the correct cconnects to have the ammunition stored for a few weeks and is flying back to Frankfurt to pick up 5Kg of his treasurers.
I once had a similar problem, my fault for guessing at the weight instead of precisely weighing my ammo. They checked the weight at check-in. To reduce the weight I had to open some sealed boxes and dump about half of the cartridges for destruction. Broke my heart but no choice.
Now I carry a digital scale to weigh what I have found at the end of each day, and temper my appetite to stay in the limit, or make arrangements to pick up my overage at a future meeting. I never leave for the area of the meeting with more than my 5Kg.
International meetings are a great way to add super items to your collection, and meet some great people, but be careful to follow the rules or real problems can occur.