Hello Matt - my suggestions would be............
The very wide and shallow pontil depression is right for the period 1810 - 1830 - very late Georgian/Regency - and the incised neck rings do occur during that period.
As for shape, I'd suggest Prussian, but I don't have anywhere near the size of decanter collection as some people here, so would bow to their more experienced knowledge if they have a better idea.
Of course, not always possible to be precise just from looking at pix on the screen, but from what you say it does appear to be a period piece from c. 1820 ish.