I just received a rising bite Rigby in 450. According to the ledger it was delivered on 22 Feb 1905. It weighs 11 LBS 6 OZ. The tops of the barrels are marked "Special 450 Bore Big-Game Rifle" and "For Special Cordite Cartridges Bullet 480 GRS"
The barrel flats however only have London Provisional, GP and V proof markings along with 450EX.

Everything points to a Nitro rifle but no nitro proofs. I assume it was probably completed a good while before it was delivered and therefor likely before the 1904 NP markings came into being. So...how do you tell for sure if a rifle made between 1898 and 1904-5 is really a full Nitro?

Thanks,
Josh