The above shell is from a Whitworth Breechloading Rifle a nice piece of lang range artillery. The gun (and consequently the shell) are classified as a 12 pounder, was made of steel and manufactured in England. They saw most of their Civil War service with the Confederate army and approximately 50 were known to be in service.
These guns had exceptional range, up to 10,000 yards and due the fact the barrel was rifled it was incredibly accurate. A 1864 magazine stated that in a test one of these guns fired 10 shots with a deviation of only 5 inches. This kind of accuracy made them incredibly effective in counter-battery fire (against the opponents artillery) and in this regards they were employed almost the same way that a sniper rifle would be deployed by the infantry.
Most of the units in service were imported via Britain through the US Naval blockade of the South, though in 1861 a single battery of the guns was fielded by the US. As effective as these guns were they did come with a number of draw backs.
The ammunition, such as that above, was difficult to manufacture and the cost of importing through the blockade made the gun very expensive to operate. It could not fire the standard ordinance of the day so it would never reach the heights of popularity. The projectile was actually a long bolt that was twisted to conform with the barrel’s rifling, so it was less of a shell and more of dart.
The second draw back had to do with mechanical issues. Originally the gun was designed as a breech-loader meaning that it was loaded from the rear. This method was faster and actually safer for the crews. However many of the guns in service developed issues with the breech as the mechanism jammed. This caused the gun to revert almost back to the muzzle-loading of a standard cannon. This combined with the cost of ammunition meant the Whitworth was doomed to be a footnote in the war’s history.