Hi 'Nando,
nice piece ......could the grooves in the ring guard be / or part of a primitive guide/fixing to attach to a musket. Would make a good bayonet. Musketeers of the late 17th early 18th C would be equipped with musket, rapier and main gauche. In battle it would be handy to have a bayonet (of sorts) without having to carry extra equipment
The grooves orientate the blade at the same aspect ....horizontal ...ideal for puncturing ribcages
All the best
David