From the proceedings of the South African Military History Society, here is one such reference for verification;

Jacobs Rifle

The relevent extract, quote;

"The subject of curtain raiser at the 13 March lecture meeting was the Jacob Rifle. The speaker, Terry Willson, has mentioned before the double-barrelled, muzzle-loading military carbine. This time he concentrated on how its development and history was influenced by the personality and circumstances of its inventor, Brigadier John Jacob, of the British East India Company's Army in the decade prior to the Indian Mutiny of 1875.
As commander of the Scinde Irregular Horse, Jacob had become increasingly frustrated with the inferior weapons issued to his Indian cavalrymen. Being a wealthy man, he spent many years and much money on developing the perfect weapon for his 'sowars'. He eventually produced the rifle that bears his name. It could be sighted to 2 000 yards (1 830m), and fire explosive bullets designed to destroy artillery limbers. It also sported a 30 inch (76,2cm) bayonet based on the Scottish claymore.

Jacob was an opinionated man who chose to ignore changing trends in firearm development, and he adopted a pattern of rifling that was both obsolete and troublesome. Nevertheless, his influence was such that during the Mutiny he was permitted to arm a new regiment with his design of carbine. It was named Jacob's Rifles.

Orders for the manufacture of the carbine and bayonet were placed in Britain, and all was set for its demonstration when Jacob died. In the hope the East India Company would honour the order, production continued for over a year. But the Jacob Rifle was never issued in India. After the Mutiny Indian troops were always armed with weapons inferior to those issued to British soldiers.

The carbines were eventually sold off as sporting rifles. The bayonets were bought by certain volunteer regiments for use as side arms. The only lasting influence of the Jacob 'weapons system' was in the design of sporting ammunition, where explosive bullets of Jacob's design were used against large game for a further 20 years."

One small but important error though, and it appears to be a "typo", the Indian Mutiny was in 1857, NOT 1875!

This puts Jacobs' development in the 1840's, well before the introduction of Purdey's percussion Express Rifles, which were for hunting purposes.