32 bore percussion with four grooves, mechanically fitting bullet with four helical ribs, I have one of these rifles, rear sight goes to 2000 !!!! Developed by General Jacob of the army of the NIzam of Hyderabad, most made by Swinburne, 24" double rifle configuration, both solid and explosive bullets were available, I have the right mould for the solid have never been able to find the special one to make the explosive bullet. Described in detail in George's English Guns and Rifles, I think there are also some references in Greener. Very accurate even to long range but fouls quickly. Most were made as military rifles with bayonet lug, mine is an "Officers" model, or at least I call it that, no bayonet lug, considerable scroll engraving, checkering at wrist and forend, otherwise identical to plain military even to big sling swivels. Very few apparently were made as pure sporting rifles and even fewer in single barrel style.