I believe some of it, like a Ranger hitting a Mexican at 100 yards with a Walker. Totally possible, I've hit silhouette targets at 100 with a Walker, no problem. But then there were claims that the Walker hits with "the same or more knockdown power as the .54 Rifle" which is an exaggeration.
Some of the stories like California Joe Head hitting a Confederate sharpshooter at 2000 yards with a scoped Sharps may be a little exaggerated. Like maybe each person who told the tale added some distance to it before it was written in someone's journal or a letter.
The story about the Union Sharpshooter who fired some rainbow like magic bullet into a Confederate camp at a "bunch of men he could just barely see" that were getting water from a stream and later found out he hit one of them at "a distance exceeding 3000 yards" , again it was probably 800 yards, a lucky pot shot and it just became 1000s of yards when the story was told later and put in a letter home and retold in a tavern somewhere "my cousin Johnny hits Rebs at 3000 yards with his Springfield musket."
Modern vets do the same thing, I do the same thing, you add some "gas" to a colorful story when you have 8 beers and 3 shots in you at a bar talking to other vets about something that happened years prior and then the story gets retold on Facebook, and become a fact ….. 30 second long firefights become 30 minutes, explosions get bigger, actions become more heroic, I can totally relate to all of the Civil War soldiers "gassing up" stories in their excitement to retell the tale of a 3000 yard shot that was really 300, but in your mind you swear you were shooting at a mile.