Enquiry about customised 1887 Winchester rifle|Winchester Rifles|Forum|Winchester Collector

I have an 1887 Winchester 1873 rifle, S/N 252018 with either R or B following the number. I would love to find out more about its history given that it does not conform to any of the models I have seen on line. It is almost exactly 100cm in total length, and in the right side of the stock is brass-lined, circular cavity, 4cm across with a hinged flap to close or open it. I can include two simple photos if someone can tell me how I do this.