Before this gets into a discussion about the cartridges here is some information about them - I bought a large amount of Eley's as per the contents of the bag - they were purchased from a dealer. The next day I happened to be shooting so tipped a box or three into the bag. I then noticed that quite a few of them were rusty. They still worked!
The next day I phoned the dealer and asked him if he knew that a lot of the cartridges had rust and he said "That's why you got them cheap!"an hour with a wire brush on a drill made quite a bit of difference.