Originally Posted by Hawg
Those aren't musket balls, they're case shot.
and its possible at least some of what is being found is case shot, as I've read "There was case shot, or cannister, first used in 1453. The name "case shot" comes from the projectile's case usually made of metal, which was filled with scrap, [B]musket balls[B], or slugs." But as to there being no iron musket balls, this site disagrees: Projectiles in the Smoothbore Era