I also am no expert on hammered coins - particularly of Charles I!
Looking in Spink and comparing with your pictures, it doesn't look to be an Aberystwyth coin to me. The bust does not seem right, the lack of crown over the shield, the missing plume before the bust...
From the description (no picture) S2791, or around that area, looks more possible? But as I understand it there are many more variations than Spink lists and I don't have (or even know of) a better book.
If you get no luck here try the hammered section on Predecimal.com - there are a few contributors there who really know their hammered silver.
Looking in Spink and comparing with your pictures, it doesn't look to be an Aberystwyth coin to me. The bust does not seem right, the lack of crown over the shield, the missing plume before the bust...
From the description (no picture) S2791, or around that area, looks more possible? But as I understand it there are many more variations than Spink lists and I don't have (or even know of) a better book.
If you get no luck here try the hammered section on Predecimal.com - there are a few contributors there who really know their hammered silver.