 Congress believed Shaw's patent was the earliest and awarded him a large sum of money based on this belief but a claim for the percussion cap was filed in 1819 and granted in 1820 as an addition to an 1818 patent by Francois Prelat, two years before Shaw's patent.Prelat may not be the inventor as he made a habit of copying English patents and inventions and the mode of operation he describes is flawed.According to historian Sidney James Gooding, the most likely inventor of the percussion cap is Joseph Egg, around 1817.