During the the last gun fight, Gilchrist takes an arrow in the right shoulder and falls. The next scene shows the Captain helping Gilchrist, but now the arrow is in his left shoulder. And in the next scene the wound is in the right shoulder again.
When Cpl. Gilchrist tells Trooper Saxton to go get him a new pick, Saxton places his shovel against the stone wall and leaves, you can plainly see the shovel start to fall. The next shot shows Saxton (below) and Gilchrist (above), but no shovel on the ground.
The Indians come through the pass into the open to attack the fort. and a lot are shot down. Later Gregory Peck when rides out under a flag of truce to speak to the Indian chief there's no bodies anywhere.
Despite his pejoratively mispronounced nickname, the surname of Lon Chaney, Junior's character, "Kebussyan," is neither Indian nor Arabic. It is Armenian. So, it is more likely that he was an ex-Turkish Janissary of Armenian descent who was brought up in the Islamic faith.
After each Apache attack the troopers are shown dropping their rifles and resting. The reality is that they would have been reloading their weapons after each skirmish.
When Trooper Kebussyan pushes over the boulder in order to kill Capt Lance, it's plausible that the boulder was oriented in an unstable position making it possible for one man to move. After it misses the Captain, it would be physically impossible tor Kebussyan to rotate that huge body significantly out of the way per the Captain's order, but the plot demanded it in order to prove the Captain correct that the situation was not accidental.
A time line was never developed. Since there was ongoing trouble between the Sgt. and one of the troopers who was formerly a rebel soldier, this had to take place during the Civil war or just after. They do mention that the Gatling gun was just developed, which would make it during the Civil war. All the troopers are carrying Winchester rifles and Colt single action army revolvers, not manufactured until the 1870's. The song, 'Little Brown Jug', is heard and it was written in 1869.
The us army was not armed with lever action rifles until after the indian wars period.
As the Colonel was still alive and one other officer had been present when he gave the Captain a Direct Order to change the assignment, word would have spread via the grapevine quickly that it was the Colonel's command NOT the Captain's decision.