What can be adjusted when sighting in a firearm?

When sighting in a firearm, the primary aspect that can be adjusted is the alignment of the sights. This process involves ensuring that the sights are properly aligned with the firearm's barrel and that they point where the shooter intends to aim. Adjusting the sights can involve moving the front or rear sight horizontally or vertically to achieve an accurate point of impact on the target.

This adjustment is crucial for improving accuracy and precision when shooting. It enables the shooter to correct for any discrepancy between where the firearm is aimed and where the projectile actually strikes the target. Proper sight alignment ultimately enhances the effectiveness of the firearm in practical applications, such as target shooting or hunting.

The other options pertain to aspects that are either fixed or not directly related to the act of sighting in. Caliber of the ammunition, the material of the firearm, and the weight of the trigger pull involve considerations that are typically set based on preference or specific firearm characteristics but do not directly influence the sighting process itself.