Great pictures - thanks for publishing them.
: The gun appears to be a Lefaucheux- style pin-fire breechloader from the 1850 to 1870 period.
: I couldn't quite see to small pin-holes on top at the breech-ends, but they must be there. The shot (or ball) shell had a percussion cap inside against the 'bottom' of the case, totally enclosed in the black powder charge. A pin of steel ran through the rim, angling down into the centre of the percussion cap. Upon being struck with the hammer, the pin exploaded the cap, which set off the charge.
: That is a lovely gun- complete with fences to protect the shooter from flash from the holes. Upon opening up the action, the pins were used to extract the empty hulls.
: As you stated it isn't chambered for rims, this tells me it is indeed a pinfire.
: When Lt. James Forsyth wrote his charming little book "The Sporting rifle and it's Projetiles" the pin-fires had just 'come out' to India. He wrote the book in 1858, published in 1860 or 61. His notes they would make a great additional gun for the battery.
: A that time, 1850 to 1860, cap-lock double rifles were the 'norm' and the "ne-plus-ultra' of hunting rifles for Dangerous Game in India. The 14 bore double rifle was apparently the ultimate choice. There were many 12's up to 8's as well, but since a hardened 15 bore ball (14 bore rifle) would exit an Indian Elephant's head, more power was deemed to be excessive along with increased recoil form larger bores.
: Due to the pin-fire's action-type and length of shell, it didn't carry the charges that were used in the muzzleloaders, hense it lacked their ultimate power. It took the English BPE ctgs. to come even remotely close, but they still lacked the power for dangerous game in India, or Africa, compared to the lowly, antiquish round ball of adequate size.