I do not want this to come across as snarky but it seems several on here have a confusion between the 2. The calibre is the ize of the bore of your rifle for example .308,.264,.284 and so on. Cartridge is the chambering of the rifle or case that we load in our given rifle. For example 300 Winchester Magnum,6.5x55 Sweedish Mauser and so on. There are times it can get confusing for instance the 308 Winchester is often shortened to just 308. I hope this will help some and if someone can clear it up a little better please do so .