Romeo-1 wrote:
> Wondering if it could be a lead ball from inside an 18th century mortar.
Definite answer:
Mortars only used explosive shells... never lead balls.
You've already answered Yes to the main question which must always be asked (was there any Artillery usage in the vicinity), so that question is settled. Next question: When a lead ball which is bigger than a musketball is found on a beach, we have to make sure it isn't a fishing-net weight... which will have a hole in it or through it. The photo shows your lead ball has a deep circular depression in it, with some beach sand "concreted" in the bottom of the depression. If you are sure that's not a hole going through the ball, or partway through it, then you might have found a lead ball which was used in Colonial-era and early-1800s "Quilted Grapeshot."
You did not give us any size-measurement of your lead ball. But, comparing it with the .75-caliber (.71"-diameter) musketball next to it in the photo, your ball seems to be approximately 1.5"-diamter, plus or minus a little bit. As you may already know, a ball's precisely-measured diameter is extremely important in determining whether or not a metal ball is an Artillery ball. But unfortunately, there is very little historical data telling the exact diameter of lead Quilted Grapeshot balls. All we know with certainty is that some were 1.0"-diameter, and some were a bit larger. So all I can tell you is that if your beach-found lead ball is not a fishing-net weight ball, the usage of artillery in that vicinity indicates it COULD be a lead ball from Quilted Grapeshot.