The inventor of a single shot cartridge carbine for the US Government was James Paris Lee.
The deal went south on a disagreement on cartridge caliber, Lee sued the US Government and won. He was so disgusted he went back to his first career as watchmaker.
Though born in England, he spent most of his life in Canada and the US. Later he went on to design the first removable magazine. His greatest claim to fame was inventing the iconic Lee-Enfield rifle. The second oldest continually used military rifle used in world.
No one got this right, most frequent answer was John Browning, second most frequent answer Samuel Colt.