Define proper buffalo rifle.
Read the chapter dealing with this exact topic in Dr. Robertson's excellent book "Africa's Most Deadly".
Otherwise, in synopsis, he recommends rifles such as the Mauser 98, Brno 600, CZ 550, and others, beginning in caliber .375 H&H or perhaps larger, depending on the individual hunter's ability.
As a side note, he has a rifle for recoil shy clients in 9.3x62 that has taken many buffalo but I will add that this caliber is legal in some countries for heavy dangerous game and not legal in others for that.
My favorite PH (Hannes Swanepoel) has mentioned to me that he really likes the Ruger No1, because when he sees a client with that particular rifle, he recons that client is a shooter and very likely to put that first bullet exactly where it needs to go, including for heavy dangerous game.
Based on that endorsement, I will guess the Ruger No1, in .375 H&H or larger, would likely be a "proper buffalo rifle", in terms of clients selecting it.
If for some unknown reason I decided that I simply must shoot a buffalo with the .45-70, for sure I would select the Ruger No1.
However, I totally cannot imagine what sort of mushrooms I'd have to eat in order to not want to choose a .404, or .416 (or .450 No2 NE like I did) or .500 Jeffery, etc.