Pic is of Teddy Roosevelt in Africa.
As Europeans made inroads into Africa in the early 1800s, guns were developed to handle the very large game encountered. This was for self-protection, food gathering, and, later and most commonly, sport. The first guns were the simple muzzle-loading shotgun designs already used for birds and loaded with solid balls of lead for use on large game. Due to their ineffectiveness on the largest game (up to 35 shots being recorded by some writers for a single elephant), they soon developed into larger caliber black powder smoothbores. The caliber was still measured in bore or gauge - 10, 8, 6, 4 bore, or even 2 bore - or the guns were named by projectile weight in ounces. The projectiles were lead round balls or short conical slugs, sometimes hardened with antimony.
These very large and heavy firearms were the first to be known as the elephant guns of the black powder era (1850-1890), though their use also included all thick-skinned dangerous game such as rhinoceros, hippopotamus and cape buffalo. Due to the velocity limitations of black powder and lead - usually around 1,500 feet per second (460 m/s) - the only way to increase penetration was to make a larger gun. The largest bore guns in common use (and bore rifles with the advent of breech loading and rifling in the late 1800s) included the 4 bore- using a 2,000-grain (130 g) slug at up to 1,400 ft/s (430 m/s). Despite their enormous power, the short low velocity slugs still suffered the penetration issues which plagued guns of this era, particularly for the toughest shot of all - defeating the bone mass for a frontal brain shot on an elephant. Thus, dangerous game hunting in the 1800s was as much a test of the gun-bearer's ability to relay guns to the hunter, and his skill on horseback in the earlier days to evade charges long enough to reload.
It was not until the parallel developments of jacketed projectiles, closely followed by smokeless powders in the late 1800s, that dangerous game could be taken with near 100% certainty.