If you can post a pic, or a set of them, folks'll be able to give you a better response. In any case, I think you've got your hands on something special.
From Reloader's Nest: "The 41 Long Colt cartridge was created in 1877 for Colt's double action "Thunderer" revolver. The front of the bullet was about 0.406"-0.408"OD. The barrel was about 0.404"-0.406" groove diameter. The case was short at 0.932"-0.937" long and the bullet lubrication was outside of the case. The base of the bullet was smaller in diameter at 0.386"-0.388"OD to fit inside the case. This is known as a "heel-base" bullet.
In the mid-1890's, Colt redesigned the cartridge. They reduced the entire diameter of the bullet to 0.386"OD and lengthened the brass case to 1.130"-0.138" in order to put both the bullet and its lubrication inside the case. The bore of the revolver was also reduced slightly to match the more popular 38-40 at 0.400"-0.401" groove diameter.
The newer soft lead bullet was made with a large hollow-base like Civil War Minie' balls. The base of the bullet expands with the pressure of the burning gunpowder to grip the rifling. It works surprisingly well, but by the beginning of WWI the 41LC was in decline and by WWII it was gone."