Most people may not know that the term "chape" means the tip-end of a scabbard, not just a buckle's tongue. Yes, you found a brass chape from a leather scabbard. Based on its shape, and its size in comparison to your hand, it appears to be from a bayonet's leather scabbard.
Need to know where you found it, to get an idea of its time-period.
I've seen a few with the exact same shape as yours (the round-tipped finial is mostly submerged in the sheetbrass sleeve) that were dug here in Eastern Virginia, but just a very few. That suggests it dates from the Revolutionary War era or very-early 1800s, rather than the civil war era... or they would be fairly common at the civil war battlesites here. Perhaps this forum's Colonial relics experts will be able to tell you what specific type of scabbard it was for.