The gun was re-proofed to 2&3/4" after the time that shot charge was part of the proofs. Originally a 2&1/2" gun I'm sure but an inquiry with H&H would confirm. I would shoot light loads in it most of the time myself, though I'm sure it would be fine with occasional 1 oz loads. CIP 2&3/4" cartridges operate at a fair bit lower pressure than our SAAMI cartridges.
Steve