Just digging up this topic, I hope someone can point you in the right direction. I watched a few cavalry/Indian westerns recently but from the description that doesn’t ring a ell.
Some black and white cavalry westerns that I know:
Fort Courageous
Fort Bowie
Only the Valiant
They’re not epics, however, so I doubt it’s any of those. As JonathanCorbett says, it could be Rio Grande. Rio Grande always felt longer than it actually is.
Only after a last attempt at reaching out. You never know. I have managed to trigger a whole number of really long passive logins over the last few weeks. I don’t easily give up on people. Leave no geek behind