I have a problem.  I'd zero my windage at 100 yards perfectly - all centered  nice and tight.  When I go to the 200 yards line, however, my groups would no longer be centered.  They would be about 2" either to the left or to the right (depending on the particular gun that I use) of the target's center line.  The aiming point that I use is the 8" X 8" Shoot 'n See square target.  This happens to me with either irons (carbine length), Aimpoint or the Prismatic.  Not sure with powered scope, because I don't have any.

What should I do?  Should I adjust the windage nicely at 100 yards and use it as the default setting (even though it is off center at 200 yards)?  Or should I re-adjust at 200 yards and leave it there (I really don't want to adjust the sight back and forth between 100 and 200 yards)?  

Many THANKS!

My apologies in advance for not being able to reply soon - I got to go to bed because I am on my graveyard shift rotation.

Do you normally shoot 200 yards?  I only need 100 so that it what I set it as.  When you go over 100yds, bullet weight and power is a big factor on accuracy.

you need to adjust your trigger finger if your groups are moving with irons and optics on different rifles.

With any zeroing, stuff that doesn't show up at closer ranges can and does rear its ugly head further out. One benefit of zeroing further out is that you know it is right on there - and at closer ranges it will be near enough it doesn't matter.  I run a 200m(219 yards) zero (not a 50/200 or other "near enough" zero - there is most certainly a difference, however slight) - and then I back track to see where my holds need to be at shorter ranges.  IMO it is always better this way round than, for instance, people who zero at 50 then just expect it to be bang on at 200 and never confirm - where it can be off not only for elevation but also for windage.  Going far to near, you will barely see any difference.

One thing you have to watch though is the wind that particular day.  With the 223 round, light wind barely has any effect at 100 yards....but most certainly does at 200 - and wind effect increases exponentially as range increases.  Unless you are zeroing on a really calm day and as you are so close anyway, I'd be inclined to leave it until you get a really good day for it.

Whether it is the right zero for you....as already mentioned by posters above, it really depends on your personal preference and the range(s) at which you generally shoot.  A 200 yard zero is however generally regarded as flatter shooting at a wider general engagement range than a 100 zero due to the bullet drop. The reason I usually run the specific zero I do is that the hardest shots in my local 3 gun match happen to be tiny plates at that distance, so that is where I most need to be dead on; and it is also a happy coincidence it is a nice flat general zero as well.

Thank you very much for the very detailed explanation.

The one in red: that is the primary reason why I am hesitant to adjust my windage at 200 yards - there seems always to be wind where I shoot at.  Another reason is because when I zero for windage at 100 yards, I use a 4 inches "strip" - so it's like having a very thin needle that I can center really well on top of my front sight post.  Seeing the group centered so nicely at 100 yds, it would break my heart if I re-adjust at 200 only to see that my groups are no longer centered at 100

I think I am going to follow your advice.  Tomorrow after work, if the day seems to be calm enough, I will re-adjust my windage at 200 yards and then "back track" at 100 and 50 to see where the POI will end up at those shorter distances.

That is one thing that I've been working on: trigger pull.  But I am really at lost, because one rifle would shoot left and the other would shoot right, so I really don't have a "base line" on how to adjust my trigger pull.  

I go back and forth between 200, 100  and 50 yards for different shooting pleasures.  I like to shoot smaller targets at 50 and 100 and at 200 yards, I use 8" X 8" squares or 12" circles.  I also paste those 8 X 8 side by side to make a giant 16" X 16" square to shoot off hand at 200 yards and from the bench at 300 yards.

I sling lead down range as a hobby, so I suppose I can live if my groups are off centered at either 200 or 100 yards, as long as I can get all my shots in the black.

I'd like to thank you all for your helpfull comments - got to get ready for work now.