The original of the rifle in the photo above and below could very well have been one of, if not, the first "sniper rifles".  It was introduced in 1855 by arms designer Sir Joseph Whitworth, with a good number of his rifles built on the British Enfield Pattern.  What made the Whitworth rifle so different is that the bore had no rifling grooves at all.  Instead, the bore was hexagonal in shape...and the bore itself spiralled with a one turn in 21 inches rate of twist.  The original bullet was a long 580 grain hexagonal bullet.  While the slow loading of the rifle ruled it out as an infantry rifle, it's tremendous accuracy made it the ideal choice for the secretive long range sharpshooters which became known as snipers.

Here's an article on hunting with a Dixie Gun Works reproduction of the Whitworth...what it takes to turn out hexagonal bullets...and the accuracy these rifles were capable of producing.  To tap the accuracy of the rifle in these photos, one of the Hi-Lux Optics long 6x Malcolm scopes has been mounted - using the Hi-Lux Malcolm off-set mounts designed for the round barrel percussion Sharps rifle (No. ROBSMT).

http://namlhunt.blogspot.com/2013/02/hunting-with-451-caliber-hexagonal-bore.html 

For more information on the Malcolm 6X Long telescopic sight, go to this link: https://hi-luxoptics.com/products/malcolm-6x-long-telescopic-rifle-scope