In spite of the official designation of .58 for the Springfield, ammo was issued to Union troops in cases marked "Cal. .577" (some were marked "Cal. .57"), and was usable in both the Springfield and Enfield. Actual diameter ranged from .565" to .585", with most running .575".
Thousands of rifles were bought by the Union from all over Europe, simply to keep the C.S. from getting them. When possible, Austrian, French, Prussian and Bavarian muskets were used to arm reserves, prison guards and the like, while the top quality Springfields and Enfields went to the front line troops.
Enfields were good guns, but were made with a lot of hand fitting while Springfield rifle-muskets were machine made and with interchangeable parts. For every story about troops with one swapping for the other, there is another story of the reverse. AFAIK, those stories were true only when Union troops armed with the old .69 caliber or decidedly inferior European muskets swapped them for captured C.S. Enfields.
Ammunition was produced in large quantities. For example, In the year from 30 June 1861 to 30 June 1862, Watervliet Arsenal alone produced some 2,900,000 ".574" (.58) musket cartridges, in addition to huge quantites of other small arms ammunition. While Frankford Arsenal would produce 1.8 million rounds of .30 ammo per day in WWII, that 1861-1862 production figure is quite good for the hand-made cartridges of the Civil War period.
Jim