Elephant gun

An elephant gun is a large caliber gun, which could be (but does not have to be) a rifle. Elephant guns were first made to be used by big-game hunters who were hunting elephants and other large animals.
Early use.
As people from Europe began exploring Africa in the early 1800s, guns were made to handle the very large animals that people saw. This was for people to protect themselves, to shoot animals for food, and later, and most commonly, sport. The first guns were the simple shotgun designs already used for birds. They were loaded with solid balls of lead that could shoot large animals. Because they did not kill large animals very easily (some writers said that it could take up to 35 shots to kill one elephant), elephant guns were soon made into larger caliber black powder smoothbores. The caliber was still measured in bore or gauge - or the guns were named by how much the projectiles (what was shot out of the guns) weighed in ounces. The projectiles were lead round balls or short slugs shaped like cones. Sometimes, antimony was put in them to make them harder.
These very large and heavy firearms were the first to be known as the elephant guns of the black powder era (1850–1890). They were not only used to kill elephants. They were also used to kill dangerous animals such as the rhinoceros, the hippopotamus and the cape buffalo. Because black powder and lead cannot go faster than about - the only way to make the projectiles go deeper into the animals' skins was to make a larger gun. Although they were very powerful, the short slugs (a type of projectile), which did not go very fast, still had problems going fully into their targets. This was especially hard for the toughest shot of all - going through the bone when an elephant's head was shot around the brain area. 
Nitro Express rifles.
Nitro Express elephant guns were first made around 1895. They used smokeless powder, which was new at the time. With smaller metal-cased bullets with sizes from .400 to .620 and speeds around , they had a much better trajectory and penetration over the black powder guns. In a few years the big bore guns disappeared from the gamefields. Early 20th century rifles came out in single shot, bolt action, and double rifle ways and were used until ivory hunting died off in the mid 20th century. Then the guns switched roles to tools for game wardens and as backup firearms for professional hunters guiding international hunters.
The American gun market made several famous dangerous gun cartridges around this time, such as the .458 Winchester Magnum, .378 Weatherby Magnum and .460 Weatherby Magnum. Many of these were 'wildcatted' (to modify an existing case and rifle to fire a different caliber bullet). The rest of the old Nitro express calibers faded to obscurity until people starting safari hunting in the 1970s and 1980s. Then elephant guns like the .416 Weatherby Magnum and the .416 Remington Magnum were made again. The .700 Nitro Express (made in the 1980's and 1990's) and the new brass manufacturers made even more powerful elephant guns such as the .585 Nyati by Ross Seyfried, .577 Tyrannosaur by Colonel Art Alphin and .585 Gehringer by Karl Gehringer to be made by wildcatters. The .600 Overkill made by Rob Garnick shows the biggest power that could come from a standard hunting action. Other wildcats based on the heavy machine gun .50 BMG and similar anti-materiel rounds have been devised which are much more powerful, though they are not generally useful hunting arms because they are heavier than .
Features.
All elephant guns have one idea in common: to have enough stopping power to prevent harm to the hunter in the case of charging game. The necessities for the gun are not only very high power (any big gun could do that), but that it can be carried for long periods, shot from any position, and be well balanced enough to track on rapidly moving animals. It is really no more than a very big hunting rifle with the same use as any hunting rifle.
Use in war.
During World War I, both the British and Germans used elephant guns taken from their African colonies when they tried to break the stalemate in the trenches. The British used elephant guns against the German tactic of having their snipers advance towards Allied lines under the cover of a large, 6-10 millimeter (0.24-0.4 inch) thick steel plate. Ordinary infantry rifles didn't do anything to the plate, but elephant guns were able to punch through it. Likewise, the Germans used a mass-produced anti-tank rifle, the Mauser 1918 TuF Gewehr, to knock out lightly armored British tanks.
During the North African Campaign in 1941, the Italians in East Africa fought against the British. The Commander - The Duke of Aosta - gave his personal collection of elephant guns to his Italian soldiers to shoot armored cars because they didn't have enough anti-tank guns.
The Finnish 20 mm antitank gun Lahti L-39 had the nickname "Norsupyssy" (Elephant Gun) during the Winter War because of its stopping power. It is not a true elephant gun, though, since it was not made for elephant hunting but as a military weapon.