Your piece-of-a-bullet shows three raised bands on its body, AND it has a small projection with a groove at the right of the third band in the photo. There were five bullet types in existence between 1861 and 1873 which had three raised bands on the bullet's body:
Confederate "Raleigh-NC pattern" .54 .58 & .69 minie-bullet (also called Carcano or Garibaldi)
Sharps .52 rifle/carbine bullet
Sharps .52 rifle/carbine "tie-ring base" (also called "ringtail") bullet
.45-70 Springfield rifle bullet (1873)
.50-70 Springfield rifle bullet (1866)
But only the .52 Sharps Ringtail bullet had a grooved projection below the third raised band. See the photos below.
Also, you say you dug it in a civil war cavalry camp... and both the US and CS cavalry are known to have used .52 Sharps Ringtail bullets.
So, that's my "best guess" about what your piece-of-a-bullet is. I say "best guess" because your bullet-piece is too incomplete and badly mangled for me to have 100% certainty about its ID.