unknown ABC part

Hi Giovanni

I think your curious part photo are components from a Sopwith-Kauper interrupter gear for a Sopwith Camel.

The following image is described as "A diagram from the maintenance manual for installation of Sopwith-Kauper synchronization (Mk.III) gear in early production Sopwith Camels (1917)" from the Wikipedia page on "synchronization gear". To me it look like a photo of a double cam interrupter gear (part A in the image below) with a cam follower (part C in the image below). It looks like the gear is propped up on a .303 bullet casing.
 
Is there a prize?

I'm glad I didn't set a prize, your answer came back too quickly.
Didn't know you knew so much about guns, I'll have to be careful. Thank you though, your explanation makes sense.

That’s fascinating  - a most impressive and speedy response!