I think I committed a mistake in this story I'm writing, the hero has a six shooter revolver in 1840, is that historically accurate?

Colt introduce its "Patterson" revolver at 1836. It is percussion thus must charge each cylinder using black powder and lead bullets and with percussion caps at nipples at back of cylinder. It have folding trigger thus no trigger guard. Is a single-action thus must cock hammer manually before each shot. It is .36" caliber. First ones have no loading lever, thus must partially disassemble to load, 1839 loading lever is added.

Not the end of the world. Colt's Patterson revolver, horrible as it was, had five-shot cylinders, so you only need minor editing.

Did you "Google"? Did you see what your library has about guns and gun collecting? "Revolvers -- History" is a Library of Congress subject heading 623.443 would be the Dewey Number.

"Rrevolvers" were first put into public production in 1836. It was a Colt

You're good. Colt's first one was in 1836.