Here's a not-too-dissimilar edge bump on one of mine to add to the discussion:

It has to be remembered that these coins were crudely cut from silver, then beaten thinner. Once the right thickness several blanks were stacked together. These were then clamped at the ends holding them in a 'sausage' shape and the cylinder of blank planchets was hammered along the edge to make them as close to circular as reasonable.
Any 'spurs' that were left from the original clipping to shape would take the appearance we see at around 3 o'clock on the reverse of my coin, where the edge curls a bit. You can also see evidence of the shearing to shape between 6 and 9 o'clock on the obverse.
My view is it's an aspect of the manufacture of the blank we see here, although a blow to the edge of the coin post-minting could also cause a similar 'bulge' I guess ..

Edit. And though it may be of no interest to you flippy, your coin once belonged to the collector Alan Morris, though I'm afraid my records don't say where he bought it.
Alan's collection was sold through a UK dealer from about 2010 - There were over 200 Charles I shillings alone, though I doubt there's much left of it to sell now.
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Edited by Tom Goodheart
03/16/2015 06:12 am