Dr. Robert et al.:

I have excavated hem weights (your lead buttons) at my site in Newbury
and have done a bit of research on them.  By the late 19th/early 20th
century these were stamped out with holes so they could be sewn into
hems and hence stay put.  The main use for them was to keep men's coat
tails from flapping in the breeze, but they also were used on women's
skirts and in draperies.  Earlier examples were just bits of lead,
perhaps flattened, perhaps not, and examples have been found in burials
of men who had their clothes on (unusual circumstances) ca. 1700.  So
there's a longish history of their use, but before they were made in a
recognizable form, we'd mistake them for lead shot, lead sprue or waste,
etc., unless the context was absolutely clear cut.

I discuss hem weights among many other sewing tools and sewing notions
in my upcoming book on the material culture of needlework and sewing.
 Watch this space!

Cheers,
Mary Beaudry
Boston U.