Charlie P is correct, as usual. It is definitely not from the civil war era (Model-1853) Enfield Rifle... because the trigger guard for those had an vertical attachment tab (shaped like a tall tombstone) on the top of its front end. The famous "Brown Bess" Enfield musket, which was the standard British Army musket from 1722 to 1838, had a similar vertical tab atop its front end. To see what I'm talking about, examine the photos below, which show a Model-1853 Enfield's trigger guard (the back end is broken off, like yours). I do not think yours had a tab which is broken off, because your photos apparently do not show a long narrow rectangular "break-off scar" where the tab would have been located. If such a scar is there but its not clear in your photos, let us know. If it's there, then it might indeed be an Enfield trigger guard.