My own researches into sharpshooting in the Civil War point to the contrary: that such was the primacy of the rifle in this period that field artillery became increasingly vulnerable to accurate rifle fire.
The most commonly used field artillery piece of the war was the smoothbore, muzzle-loading Napoleon 12-pounder, which fired solid shot (with a five-degree elevation) out to range of just under a mile and had an effective anti-personnel canister range of around 400 yards. By comparison, the Springfield and Enfield rifles that were common on both sides had an effective range of roughly 200-300 yards against infantry, although according to data in Greener’s The Gun and its Development (1910) the Enfield could hit artillery-sized target out to 500 yards.
While decent shots armed with Springfields and Enfields could force artillery back beyond the effective edge of canister range, it was a different type of infantryman armed with a greatly improved rifle that caused the real damage. The Union armies deployed sharpshooters equipped with breech-loading Sharps carbines and Spencer repeating rifles, which had improved accuracy and provided a much greater volume of fire. But it was the crack shots of the Confederate forces, armed with the accurate muzzle-loading, British-manufactured Kerr and Whitworth rifles that inflicted the heavy casualties against artillerymen and other high-value targets who included officers and rival sharpshooters.
Although some historians of the Southern cause get carried away when recounting the exploits of the Confederate sharpshooters and their weapons, the Kerrs and Whitworths were rugged military rifles with the accuracy of competition weapons – where range firing out to 1000 yards was commonplace (the four-power telescopic sight on the Whitworth was calibrated to 1500 yards).
Although sharpshooter numbers were small, their effect was great. I include below a few first-hand accounts of Confederates using Kerr and Whitworth rifles against Union artillery to show the damage they caused. John West, one of several Whitworth-armed Georgians fighting in General Robert E. Lee’s Army of Northern Virginia, wrote:
‘Artillery could stand anything better that they could sharpshooting, and they would turn their guns upon a sharpshooter as quick as they would upon a battery. You see, we could pick off gunners so easily. Myself and a comrade completely silenced a battery of six guns in less than two hours on one occasion. The battery was then stormed and captured.’
Sam Watkins, an infantryman from Tennessee, contributed this narrative when his unit came under fire from a Union artillery piece in Georgia:
‘“Hold on boys,” says a sharpshooter armed with a Whitworth gun, “I’ll stop that racket. Wait till I see her smoke again!” Boom! Boom! The keen crack of the Whitworth rings upon the frosty morning air; the [Union] canoneers are seen to lie down; something is going on. “Yes, yonder is a fellow being carried off in a litter.” Bang! Bang! Goes the Whitworth, and the battery is seen to limber off to the rear.’
An example of Confederate sharpshooters being used alongside their own guns during counter-battery engagements is related here by Johnny Green, a soldier in the famed Kentucky Orphan Brigade:
‘The enemy came at us pretty early. We had the advantage of position, having posted our battery so it would sweep that road for nearly a mile. We hid our sharpshooters also in the edge of a swamp and when their battery would reply to ours those keen-eyed marksmen would pick-off their artillerymen, so that our battery had much the best of the fight.’
The rifle’s domination of the battlefield would be short lived, however. In 1870 – just five years after the end of the Civil War – the steel, breech-loading Krupp guns of the Prussian Army – with a range of 4500 metres – would be used to devastating effect against the armies of Napoleon III. Further improvements in artillery design and the development of effective machine guns brought this 'golden age' of the rifle to a close.