"...500 grainers won't cycle through a Marlin 1895..." Anything can be done in a movie. You don't have to reload in movies either.
How can you tell the bullet weight by just seeing it in a movie? Still likely a .45-70 as .444 Marlin blanks or DP cartridges would have to be made. .45-70 has been used in movies since before D.W. Griffith.