Goofs

The dynamite John hands Juan before the bank raid is several sticks in a bundle, with a single fuse and cap in the center, but, when Juan dynamites the vault door, he uses two single sticks, individually fused and capped.

When Sean sets his machine gun back on its tripod after setting the charges, it is loaded with a section of belt with no more than (possibly) fifty cartridges; he is never seen to reload it, but fires many more shots than that. Also, when he stops shooting, it is because the gun has run out of ammunition. We can clearly see the end of the belt go through the action, leaving empty links hanging on the right side, and no belt at all on the left side. But, in later shots, there is a belt with unfired cartridges visible on that side, though it seems to change length between shots.

When Juan is robbing the 'bank' in Mesa Verde, and he shoots open the second door in the basement, we see what appears to be a soldier (khakis, long jacket, knee boots, Sam Brown belt) round the corner on the stairs and casually continue walking down them.

When the deserter is taken from the train to be executed along with two others, the wall behind him is shot at and damaged on both sides of the deserter. The following close-up shot of the deserter getting shot in the back reveals no damage to the wall.

During the executions in the rain, when Mallory sees Villega identifying rebels, the speed of the windshield wipers changes. In one wide angle shot, the Col is shown manually moving the blades at a relatively slow rate. In other shots, the blades are moving much faster and with less jerkiness than when seen with the manual movement.

The bank door exploded outwards. It should have exploded in since the dynamite was placed on the outside.

In the train wreck sequence, some of the miniature shots of the explosion and the train being destroyed were not printed in proper anamorphic format, and are badly distorted.

When Juan's youngest son is shown lying dead, the actor can be seen breathing.

Juan rests his hand on the barrel of the machine gun from which he just fired hundreds of rounds. He would've burned himself.

Of all the characters living in poverty, being dirty and all, none of them (especially Juan who smiles a lot) has a broken tooth. Just shiny white smiles, not realistic at all.

In the train, the automatic pistol that Juan Miranda uses is a Browning GP35. As its names suggests, this model became available in 1935 (so a contemporary of the aforementioned MG42).

Although the action takes place circa 1914, when Mallory's possessions are rifled by Miranda's family, a flag with the legend "IRA" is pulled out. The IRA was not formed until 1919.

Irish nationalist Mallory owns an IRA flag, but the movie is set in 1913 and IRA and its flag did not officially exist until 1919. Mallory could have been a member of IRB (Irish Republican Brotherhood) instead.

In the first scene, where Juan holds up the stagecoach, one of the children in the bandit gang is holding a Spanish double action pistol, an Astra 400. If this movie were to take place in 1914, the Astra 400 model would not have been invented yet, as it was put into production in 1921.

The newspaper that John Mallory is given in the "surgical operation" scene reads in the right column "Y el mundial lo ganó Pelé... que es el rey... balón", which would be translated as "And the Soccer World Cup was won by Pelé... who is the king... soccer ball". Famous soccer player Pelé was not even born in the 1910s, and neither did the World Cup even exist in the first place.