.400NitroExpress.

Since the gun I will be looking at, has the exact same distict side bolsters, I will assume it was made for Lyon & Lyon by the Trades ( Specifcally Osborne ).
I will be looking for either "Nitro Proved" if proved before 1904 or Crown over NP ( Birmingham post 1904 )
I would not expect to see sword over NP ( London post 1904 ).
I will look for the crossed swords with numbers, what does this signify ?
I will also take pictures of the other marks ie "450EX" "480grs" "70grs Cordite MAX"
Crown / BV (Viewing mark) Crown / BNP ( Nitro Proof )
Serial # 438XX Lyon # 9XX.

I will also be inspecting the bores for pitting, frosting and general wear.
I will be bringing some dummy 450NE ammo to check the chambers.

Hopefully it checks out, and the price is right.

Regards
Nitro450exp