I'm pretty much lined up with Greyhawk on this except for the rifles. I think big bore rifles start at 40cal. Back in the day the .40-65, .40-82 and the .405 were considered 'big medicine'. TR made a name for himself as a big game hunter using the .405Win. I think today many African nations draw the line between medium and big bore right between the 375 and the 40cal. I think most of us would agree with that logic if we fired a box of .416 Rem Mag from the bench.