I'm answering your question. The first part of your question was about the diameter of the barrel.
On the second part of your question, about the number of joules, I would answer that this is absolutely the case. We need only think of all calibres of the Cheytac and Wildcat firearms, which are used in Africa as well as in western Canada to hunt what is called big game.
The problem is that the lack of knowledge has caused confusion on this issue. There is an entire definition for armour piercing firearms that differs enormously in terms of the number of joules required and the type of ammunition needed, which is not available on the market. However, for hunting big game, those firearms are entirely necessary. If you have even a little respect for the life you are preparing to take, to harvest game for your family, yes, it's absolutely necessary.