Please explain ballistics and pellet weight...

[Kingston73]

I completely understand why different weight pellets and different shapes will have different point of impact vertically, but what makes a pellet have a different horizontal poi?  I'm still learning my xs25 and most of the pellets I've tried went basically where I expected.  I zeroed at 20 yards using crossman premier domed 14.3 g pellets (.22 cal). Rws wad cutters are about an inch high but still in line, same with jsb strattons.  The one that surprised me was the beeman Kodiak pointed 21g pellets.  They have the same vertical poi as the crossman but they impact about an inch to the left of my point of aim. 

So why do pellets that are about 6 g heavier have the same vertical but consistently land to the left of poa?

[rsterne]

Likely barrel harmonics / vibration....

Bob

[Bullit]

Yep.  There's some informative videos online, that show how much these air rifle barrels do move.
Finding that "balance" of pellet to power of your rifle is part of the fun!  You also may find that after it is cleaned again, and finally gets broken in...the pellet choices may also change.

[Booger]

I have noticed the same thing with JSB 15.9 grain vs H&N FTT. My rifles shoot JSBs better so it does not bother me.