It's important to note (as my original post did) that in the complete-cartridges photo, only #2 and #3 are definitely .45/70 cartridges.
Counting from the photo's left, cartridge #1 is a .50/70, and cartridge #7 is a .44/70 Sharps. I'm not certain enough about the ID of #4, #5, and #6 to name them here.
LifeIsGood, the relic you dug is definitely a .45/70 bullet. First manufacture was in the 1870s, for the 1873 US .45-caliber Springfield rifle and carbine -- and used in the Indian Wars through the Spanish-American War. Specifically, your bullet appears to be a .45/70/405. As I mentioned in the original thread, I myself dug one at the Fredericksburg VA battlefield (about one mile outside the Battlefield Park boundary). Many civil war bullets and artillery shell fragments came from the same farmer's field where I dug my .45/70 bullet. It was about 1/4 mile from the campsite of Fredericksburg's Span-Am War soldiers (which is marked by a memorial monument which gives that information).
Explaining the three numbers in your bullet's ID... the first refers to its caliber, the second to the weight of the cartridge's powder-charge (in Grains), and the thrid number refers to the weight of the lead bullet itself (also in Grains).