I have found only one reference to a firearms retailer called McCarthy, Buck & Co, which traded from 40 St Andrew’s Hill, London EC, in 1899-1900 and may still have been in business up to 1914.
It is not possible to give an indication of a gun’s value without a detailed examination.
The value of a shotgun is a complicated equation based on many factors, including build quality, mechanical condition and features such as barrel length and whether or not it is an ejector.
It is unlawful to sell or offer for sale a gun that is not in proof.
This can only be ascertained by the use of sophisticated measuring gauges.