Looks like your friend was lucky enough to find a reasonably high grade Greener.

The F stands for Facile Princeps (translated as "easily superior"), Grrener's own patented boxlock action design. It was very close to the Westley Richards Anson & Deeley design and was the subject of a pitched high court battle over alleged patent infringement in the late 1800's, but WW Greener managed to make it stick and built many (if not most) of his high-grade boxlocks on similar actions.

The 17 is the original price of the gun in Guineas.

Does it have ejectors? Some were fitted with Greener's own Unique ejectors which can be an absolute bitch to repair if something goes bust!

Post the serial no and I may be able to dig up the year of manufacture for your friend.

Regards

JvW

PS: What's its condition?