"Precision" weighing, and diameter measuring, are crucially important for correctly distinguishing an actual cannonball from the many lookalikes which are NOT artillery balls. You say this ball weighs "exactly one pound, which causes me to assume you weighed it on a precision scale which said 1 pound 0 ounces. If that is the case, its precise weight and diameter of 1.95-inches (not counting the rust-encrustation) would indicate it is a 1-Pounder caliber cannonball, from the Colonial Era into the early-1800s. Its weight and diameter also indicate it is made of cast-iron, and not steel, which is a heavier alloy. (A steel ball of 1.95-inch diameter would weigh about 1 pound 1.6 ounces.) There were no steel Field Artillery cannonballs, so your ball being made of cast-iron keeps it in the cannonball category.
I checked the historical data on diameters-&-weight of Grapeshot and Canister-ammo balls used in America, and can tell you that your ball's diameter and weight don't match up with any Grapeshot or Canister balls.
