These are the Model 1855-1861 Springfield bayonets. The 1855 Springfield Musket was the first 58 cal. musket used by the US Military. It used Maynard priming system. Something like what cap guns shoot today. The Model 1861 Springfield used the percussion cap to ignite the gun powder. Both used the same bayonet. This bayonet was used up through 1865 until the end of the war, and black powder muskets were starting to be fazed out and replaced by the cartridge rifle.