What you have is a really nice projectile. This is a Sawyer Rigid Walled Canister. They made it in 3" and 3.67" and 3.4" calibers with the 3" not seeing any battlefield use. However the 3.67" caliber saw use in Port Hudson and the 3.4" have been recovered at Harpers Ferry. If you have the Dickey and George artillery book it can be found there; page 62 & 63 in the 1993 edition. I'm suspect it is also in John Biemecks incredible books as well.
Does the top say "3.2"?