I find quite a few similar lead objects, some like that, some cut up. I think they call them lead 'pancakes'. The easy way to 'harvest' lead is to melt it into a shallow 'dip or bowl' made into a few inches of sand. A very simple moulding technique used since the Roman times. These 'pancakes' were easily transportable by person & bits could be cut off to cast muskets balls or bullets or repair holes in objects.
Of course being lead it may have just been melted from any other number of items by accident. However, the regular shape makes me believe it was deliberate.
Basically a kind of primitive 'homemade' ingot.
Below is a more 'official/regulated' modern version that has been stamped; (but the shape is the same etc..) Clearly mine is broken but would have be the same shape & profile.
Yours looks at least 100++