Not an elephant gun, unless the Spanish Army in Cuba was hunting elephants there.
I'm certain that those three cartridges are 11.5x57R Spanish Reformado cartridges.
It was the original cartridge for the Spanish Remington Rolling Block rifles, adopted about 1867.
Quite a few of the rifles and cartridges were sold by Francis Bannerman in the years after the Spanish American War.
US forces captured thousands of rifles and millions of rounds of the ammo when we took Cuba, Puerto Rico, the Philippines, and other Spanish colonies.
"The gift which I am sending you is called a dog, and is in fact the most precious and valuable possession of mankind" -Theodorus Gaza
Baby Jesus cries when the fat redneck doesn't have military-grade firepower.