Musket ball markings

[Milmed]

Hi,
I assume what I have is a musket ball but need help identifying the markings.

There are two strips that cross over each other and encircle the full circumference of the ball. A third strip also runs diagonally to these two, also around the full circumference of the ball

Where the two strips converge are 4 circular indentations (see picture) and each indentations holds a value . The lower one in picture is the letter 'Y', to the left is the letter 'O', to the right appears to be a shield but could be an incomplete letter and the top mark is not identifiable due to damage.

size of ball approximate 17-18mm

Any assistance as to what the markings indicate, and if it is indeed a musket ball and what period it my be from.

Regards
Steve