From Writer's Digest Thoughts on Historical Research by Michael Zimmer
Be Wary of Historical Mistakes
"Sometimes, even what seems obvious can be incorrect. Want to give a wagon train scout an 1873 Colt Peacemaker on his journey to the Montana gold fields? The odds are that if you date your story any earlier than 1875 or ’76, you’re going to be perpetuating a myth already heavily solidified by decades of Hollywood films.
Even if historical fiction isn't your genre, every writer needs to be vigilant about the details.
Do they drink pop or soda in the northeast? Are they mixing up egg creams in Brooklyn?