Brigadier-General John Jacob
One of the more unusual sharpshooter rifles was the Jacob’s, the brainchild of John Jacob, one of those brilliant, eccentric British Army officers who spent his career in India.
He had spent 25 years improving rifled firearms, carrying on experiments unrivalled even by public bodies. A range of 200 yards sufficed in cantonments, but at Jacobabad he had to go into the desert to set up butts at a range of 2000 yards. He went for a four grooved rifle and had numerous experimenal guns manufactured in London by the leading gunsmiths and completely at his expense.
Jacob, like Joseph Whitworth, was renowned not only as a soldier but as a mathematician, and his rifle was as uncoventional as its designer. Rather than using a small .45 caliber bore Jacob stayed with more conventional .57-58 caliber (Bill Adams theorizes that this would allow use of standard service ammo in a pinch). In any case his rifle used four deep grooves and a conical bullet with corresponding lugs. Though unusual the Jacob’s rifle, precision made in London by master gunsmiths like George Daw, quickly gained a reputation for accuracy at extended ranges. They appealed in in particular to wealthy aristocratic scientists like Lord Kelvin, who swore by his. Jacob wanted to build a cannon on the same pattern, but died early at age 45.
Only a few Jacob’s were used during the American Civil War, and those were privately owned, usually by men able to afford the best. I do have one account of one of Berdan’s men using one (the chaplain, Lorenzo Barber), who kept one barrel of his double rifle loaded with buckshot and the other with ball.