The British .577 Snider-Enfield is a type of breech loading rifle. It was one of the most widely used of the Snider varieties, (the action 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 trials, the Snider Pattern 1853 conversions proved both more accurate than original Pattern 1853s and much faster firing as well. From 1866 on the rifles were converted in large numbers at the Royal Small Arms Factory (RSAF) Enfield beginning with the initial pattern, the Mark I.

New rifles started as Pattern 1853s, but received a new breechblock/receiver assembly. Converted rifles retained the original iron barrel, furniture, locks and hammer. The Mark III rifles were newly made, with steel barrels which were so marked, flat nosed hammers, feature a latch-locking breech block.