Writer Elmore Leonard certainly did know something about classic firearms. From Frank Harlan's Custom Savage 99 (1899), Olin Mingo's Remington-Keene sporter (1880) in .45-70, Lamarr Simms Mauser C-96 (1896) broomhandle, and Joe's Cased Ross Rifle sporter model M-10 (1910) in .280 Ross. Leonard took special care to ensure all weapons (even the optics) were period accurate for that movie, being set in pre-statehood New Mexico territory (1912).
In the original script, Luis Chama was a more heroic and multi-layered character, but Clint Eastwood wanted to be seen as the hero, so this was changed throughout filming. John Saxon said "Clint needed to be the guy who dealt with all the action, so in the end, Chama was smeared with self-serving and cowardice, so it was clear who the main hero was." Saxon attended a NOSOTROS meeting, a Latin American organization opposed to stereotypes, and publicly apologized for playing such a dubious character.
The exact date of the movie is not given, but judging by the number of stars on the American flag flying on top of the Sinola County courthouse (45 stars), it would imply that this movie is set between 1896 and 1912. Utah was admitted into the Union on 4 January 1896 as the 45th state, and New Mexico was admitted as the 46th state on 6 January 1912.