Trajectory questions: Different bullet weights

[Bacchus]

Are there general rules about the trajectories of bullets (within the same caliber) that differ in weight alone? I'm talking about factory loaded ammunition.

For example, let's use the 308. Say I have a rifle sighted in at 100 yards with a 165 gr bullet. What would happen if I switched to a different bullet weight, perhaps a 150 gr or even 180?

 

[Steve Smith]

Well, generally speaking, the lighter bullet will go faster initially. Downrange, the lighter bullet will lose speed more quickly, and the heavier bullet would "outrun" it becuase it loses its speed at a slower rate.

 

[Jim Watson]

Trajectory differences at that close range are next to nothing. All things being equal, they would shoot into the same group or at least overlapping groups. But there are other factors. Differences in barrel vibration could put them to different points of impact. You just have to do the shooting.