jorge (..and subsequent posters!):
You need a more open mind on this subject!
Here in Australia's Northern Territory, many hundreds of buffalo have been laid low over the years with the standard 1 1/4 ounce Brenneke shotgun slug fired from various smooth-bores, most frequently the CBC break-open single-barrel gun! With a side-on chest-shot, the slugs typically pull up in the off-side ribs or under the hide after penetrating the chest cavity. We're talking ~550 grains of hardened lead at 1500 fps, not your average 1-oz Foster POS!

Hell, even one of your countrymen has decked an American buffalo with Brennekes recently, read about it in the latest American Slug Shooting Assn Newsletter.
He even includes a pic of the recovered slugs! Beautiful!

BTW, not defending the "dangerous game in Africa" claims, just pointing out that there is a gross underestimation of the effectiveness of the purpose-built modern base-wad shotgun slug in jorge's last post.