It is definitely a civil war era Bormann time-fuze from an explosive cannonball... and yours is a Confederate-made one.
Here's how to distinguish CS-made ones from US-made ones:
The small raised lines spaced along the inner edge of the "clockface" on the fuze's front designate seconds and fractions-of-a-second of time.. such as (going clockwise):
1-second
1-&-1/4 second
1-&-1/2 second
1-&-3/4 second
2 seconds.
The Confederate-made version always had two raised lines to the left of the number 1 (those two lines representing 1/2-second and 3/4-second). The yankee-made version had only one raised line to the left of the number 1 (that line represents 3/4-second). In other words, the Confederate Bormann fuze's time-markings "start" at 1/2-second, and the yankee version at 3/4-second.
Because yours still has dirt on its front, and some of its time-numbers are corroded, and you'd never seen a Bormann timefuze until you found one... here are some photos which show several varieties of them, cleaned up, and in unusually fine condition. (Most that we find are badly damaged from the shell's explosion, and/or badly corroded.)
In the photo showing six varieties, the top row is yankee-made, the bottom row is Confederate-made. In the photo showing nine varieties, the only Confederate-made one is in the center of the photo.
