That photo appears to be of the front side of the early (pre-1920) style forearm collar for a takedown rifle. The 1899 F is a solid frame rifle, so it would not have a forearm collar, and I am not aware of there being a takedown option for the 1899 F. Thus I can't speculate on the significance of the F on the piece in the photo.
We know Savage wasted very little and that receivers were not necessarily assembled in serial number order. Maybe it came off a very early 99 F, and they used up an in stock forearm collar.
Last edited by Jaaack; 08/21/19. Reason: Added last comment.
