Well said Hoyt
Brent, that load stops both the bus
AND the driver. It's not rocket science. It's pretty much all there on Hodgdon's .45-70 Modern Rifle loads. I use a .405 Remington and slightly less IMR 4198 on the max end. It works. 1950 fps. A 400 - .405 hard cast would work also. Asian buffs ain't armor plated, they're not an African Cape Buffalo. I have no reason to believe an '06 with the right load wouldn't work. More than a few elephants have been killed with them, so I don't know where that farmer is coming from. I believe most farmers are not gun experts....and I'm a farmer.
In Italy, where I lived for three years, farmers milk Asian Buffs and make Mozzarella Cheese. It's the preferred cheese, very rich. Throughout the Eastern world, they are beasts of burden, as well as food and milk. In my opinion, three grand to shoot one is a bit much. It's more than the average Third World farmer sees in a year. You could shoot a prime Angus Bull for that or less. Depending on the level of domestication, it could be like shooting Holsteins at a dairy barn, or they could be wild and more of a challenge......I don't know.
Good luck and let us know how you make out.
Pete