I am not sure of the numbers from the pictures, but could it be Pat. 324 from 1870 ?

British Patent 324 of 1870, registered in England, was granted to J. Thomas, a Birmingham gunmaker, for an improved single-bite, snap-action mechanism for shotguns. This patent, often referred to as the Thomas patent action, was significant in the development of breech-loading firearms and was licensed or used by various gun manufacturers during that era.

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