Beautiful rifle as are the other Rigby's posted recently.
They all appear to show very high quality workmanship.

Regarding the '3' shown on the grip trap, it's possible that this is only the third SIDELOCK Rigby 500 NE double ever built!

Harald Wolf wrote in Hatari Times that only 2 Rigby sidelock 500 NE's were built during the 20th century.
The first was finished in 1908, and the second much later in 1993 while Paul Roberts was at the helm.

This one might be #3!