Again, getting up from my sickbed to answer a request.
There are multi-millions of small (less than 2 inches in diameter) iron/steel balls -- most of which were manufactured for industrial or machinery purposes (such as ball-bearings), not made as artillery ammunition.
Therefore, the only thing we can do to ID such a ball with even semi-certainty is, get a super-accurate measurement of the ball's diameter, and see whether its diameter matches up with anything in the size charts in the civil-war-and-earlier US Ordnance Manual Of 1861. Of course,
all of the rust-&-dirt encrustation must be removed to get a truly accurate iron-only measurement. If the diameter measurement you get from the cleaned ball is a dead-on match (within 2 one-hundredths of an inch) for an artillery ball in the Ordnance Manual, then you'll know with certainty.
For example, the Ordnance Manual says a 6-Pounder caliber artillery Canister was specified to be between 1.14" and 1.17" in diameter.
All of the above having been said... because you reported that you found it near a "Colonial" cellar-hole, it
could be a Colonial era Quilted Grapeshot ball. I say "could" because the diameters of the balls in the many sizes of Colonial era Quilted Grapeshot ammunition are not known. Unfortunately, there is no Colonial time-period equivalent for the Civil War Ordnance Manual. In other words, there's no way to prove or disprove your ball from being a Colonial Quilted Grapeshot ball.
So, all you can do is clean every bit of encrustation off your iron ball and check its precisely-measured (use a Digital Caliper) diameter with the 1861 Ordnance Manual artillery-ball size charts.
Cannon bore, shot, and shell diameters for smoothbore guns
The only other thing I can say at this point is, because Grapeshot and Canister artillery ammunition contained dozens of balls, when you find one of those balls, there's usually more than just one ball at the spot where you dug it. If you can't find even one other ball like that one at the dig-site, it is "unlikely" to be a Grapeshot or Canister ball