The Springfield Model 1861 was the standard rifle used by Union infantry during the Civil War. The rifle was produced in Springfield Massachusetts, which is where it got its name. The total weight of the rifle was a mere 9 pounds.
Roughly 700,000 of these rifles were built between 1861 and 1865. This was not the greatest weapon of the era however it was the most widely available and since it was a one shot muzzle loading rifle Union command did not need to worry to much about being able to supply the ammunition for them.
The rifle was accurate however in the hands of troops who had little to no training in shooting often missed their targets, typically shooting over the heads of the enemy. Accuracy during this time was less important than raw firepower. Leaders used mass volley attacks to defeat their enemy. This tactic meant that accuracy of the individual soldier meant very little.
This rifle would essentially become the last muzzleloader to be used in warfare after the Civil War ended. Technology was already moving ahead with repeaters even during the war. The reason the Union did not switch to using nothing but repeating rifles was simply because the Springfield was readily available and it did not waste large amounts of ammunition.