I was talking to my brother about George Fraser's "Flashman and the Redskins", and somewhere along our discussion he brought up an anecdote from one of his coworkers. The guy told him a story (and it may just be a story) that a person in Custer's troop brought a real gun to a reenactment of the battle of Little Bighorn in the late '70s. He shot 10 people participating as indians before someone on that team grabbed a real tomahawk and killed him.
In this story, Mr. Tomahawk ran away and was later hunted, along with some of his associates for whatever reason, by "concerned citizens". The townsfolk tracked down only one of them and scalped him alive as some sort of ironic punishment. I guess. Anyway, my brother's coworker went on to tell him that the army was eventually brought in to take down the whole lot of them. They did. When they faced off, the group of First Nations people were on horseback, but didn't hold a candle to the military and were shot dead.
Neither myself nor my brother could hardly even begin to dispute it because it was wholly possible. Anyway, we're wondering:
How likely is it that any of this is true?
Are there any records of such things?
A massacre of Indians on horseback in Montana in the 1970s? No, that didn't happen - or if it did, there seems to be no record of it anywhere, which is hard to believe in the days of color TV. Your brother's coworker may be mistaking (and considerably embellishing) the Wounded Knee standoff. The media coverage this event received makes me skeptical that your mass murder/vigilante action/Army massacre of Native Americans managed to escape any mention in the historical record, especially as it allegedly happened within just a few years of Wounded Knee.
I have been a "Custerologist" for decades and this is the first time I have ever heard this tale. It is fiction.
Both Robert M. Utley and Jerome A. Greene, distinguished former NPS staff and renowned historians, have written extensively on Custer, the Battle of the Little Bighorn, the history of the Little Bighorn Battlefield National Monument and all things Custer in general (no pun intended.) Both served for years in positions at the Little Bighorn Battlefield National Monument. Neither has ever made any mention of such a fantastical event.