I would if I was concerned print out stickers for the ammo boxes with .280 Ackley Improved on the stickers etc.

This is an occasional problem in a lot of countries which are touchy with firearms or when encountering an 'enthusiastic' officer at an airport/border with custom and wildcat calibres. Just one issue you may have to cope with if choosing to use a wildcat or custom cartridge.

If it was me I would just do the sticker thing, have some photocopied pages on hand for reference, and just bluff it through.