From
The Buffalo Harvest:
"Don't understand that any official action was taken in Washington and directives sent out to kill all the buff on the plains. Nothing like that happened. What did happen was that army officers in charge of plains operations encouraged the slaughter of buffalo in every possible way. Part of this encouragement was of a practical nature that we runners appreciated. It consisted of ammunition, free ammunition, all you could use, all you wanted, more than you needed. All you had to do to get it was apply at any frontier army post and say you were short of ammunition, and plenty would be given you. I received thousands of rounds this way. It was in .45-70 caliber, but we broke it up, remelted the lead, and some runners used government powder. I didn't. I was a stickler for the best, and used imported English powder which I will be describing to you in a little while. I had no trouble trading my government powder for things I wanted -- tobacco, bacon, flour, and other things."
Now, y'all may be right that it was the .50-70, but I am just quoting what Frank wrote. The book was published in 1958, four years after his death. He died at the age of 104. I don't know when he wrote it. Maybe some of the details had been "blurred" from the time he experienced it until he wrote it down.
You can read his book online at:
http://www.pbs.org/weta/thewest/resources/archives/five/buffalo.htmSlim