G'day Dan:
That chambering is a new one on me.
...unless it is the .577 NE (3-inch).
Verney Carron do list the full-nitro .577 as an option for their African Game Double Rifles in current catalogues.

Long-time members here will know that I favor the Light Nitro loads!

Anything from the .577-650-65 to the .577-650-90 (in old terminology). They are lots of fun to shoot without getting belted around by the 750gr full loads.

Should be nothing wrong with a full-nitro VC though if it is weighted correctly. The Brits built them at 12-and-a-bit lbs up to nearly 15 lbs, and they need to be about 13 lbs or so for comfortable shooting IMHO.

I have shot a VC .450 NE a bit with nothing bad to say about it. Weight distribution seemed better than Merkel/Sabatti etc. Even started to get used to the Wundhammer pistol-grip!