It's a Snider-Enfield.
The firearm action was invented by the American Jacob Snider. It was adopted by Britain as a conversion system for its ubiquitous Enfield 1853 rifled musket muzzle loading arms.
In service 1867–1901
Used by United Kingdom & Colonies, Japan, Turkey, Portugal, Egypt
Wars British colonial wars, New Zealand land wars
, Red River Rebellion, North-West Rebellion, Fenian Raids, Anglo-Zulu War, Boer War, Boshin war, Russo-Turkish War.
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Many different patterns of it on this page;