Mal, I have looked through the early records and no mention of Roualeyn Gordon Cumming so you are right in thinking he may have bought it second-hand. Look out for an extract about his Dickson rifle in the new Dickson book though.
As for which rifle it could be, this is difficult as not calibres are recorded and some shotguns had additional rifle barrels fitted and the calibre of the rifle barrels is not recorded!
The rifles that passed through Julias in the last few years were No.1087, a double 8 bore and No.1089, a 60 Cal double.
There was a lot of press coverage in Edinburgh during the 1850's on the trials of Dicksons two-groove rifles and how well they worked and how accurate they were. Dickson built a small number of long-range experimental rifles which were sighted for 1000 yards and was one of the first companies to introduce a telescopic sight to benefit the range of the rifle in 1850 (rifle No.1406). Dickson's were building this type of rifle from the mid-1830s, some 20 years before Purdey coined the term 'Express'!
