I'm thinking a Phased Plasma Rifle in the 40 watt range or the the old standby; 10mm Caseless, Light Armor Piercing, Pulse Rifle with Grenade Launcher.
If you can get the Terminator or the Colonial Marines from the Aliens movies to loan you one that is!
Are you expecting or going somewhere that you might be subjected to such a charge?
I once saw on some animal show filmed in Africa a story about a group of elephants that had to be destroyed. Six to ten animals as I remember, anyway four "game keepers" drove up the the animals in a Range Rover. The four, armed with HK91's, dropped the herd in it's tracks in a matter seconds. As you can guess each animal took multi-hits, but ammo is cheap.
If I really was expecting a charge like you say, not hunting, just beating off a wild charge,,,,,, M1A from Springfield Armory or HK91. Not sporting at all, but will do the job.
A BB on target is better than an artillery shell that misses.