Manufactured in 1861. The Jacob rifle was invented by General John Jacob. An officer of the British East India Company, Jacob commanded a cavalry regiment called the 36th Jacob's Horse. He invented the rifle with the aim of firing explosive "caisson killer" bullets to knock out enemy artillery at long range. He wrote, "Judging from our practice at Jacobabad, it seems certain that two good riflemen so armed, could in 10 minutes, annihilate the best Field Battery of Artillery now existing." A well-placed shot into a caisson would cause a large explosion that could destroy both an artillery piece and its crew. He intended to arm the 1st Regiment Jacob's Rifles with his distinctive double rifles, but he died before the order for the rifles was filled. Some do appear to have been issued to the unit, and the rifles saw at least limited use in the American Civil War, including by chaplain Lorenzo Barber of the Berdan Sharpshooters with one barrel loaded with buckshot and the other with a solid projectile. This example has the distinctive four-groove rifling in the 32 bore left barrel for a winged bullet, and the right barrel has been bored out to 16 bore smoothbore and lacks the usual lug for mounting a sword bayonet. The stock also has a checkered wrist. The lock plates are each marked "SWINBURN & SON/PATENT/1861." The patchbox is marked "JACOB'S RIFLES" and contains some winged bullets. Behind the ladder rear sight, which is graduated to 2,000 yards not including the top notch, is a three leaf express sight graduated for 100 to 300 yards.

Fine with 75% plus of the period reblued finish on the barrels, patches of bright original case colors, gray and brown patina on the balance, patches of mild pitting, and general mild wear. The period refinished stock is also fine and has crisp checkering and mild scratches and dings. Mechanically fine.