I do not know what the 304 is.
The choke I will leave for someone else.
The barrels weighed 2.62 lbs when proofed.
It was proofed in 1942. The Controller was Hubert Charlier.
It passed the smokeless powder proof.
It was proofed at the Liege Proof house.
The gauge is 16 and the chambers are 2 3/4".

Pete