So I was trained by uncle sam to shoot iron sights and I do it really well, but I am having a hard time adapting to red dot sights.  They seem to be much more range specific than irons are.  With the M-16, we would zero and then be able to hit anything from 25 to 300 meters with just a little hold over.  when i sight my red dot on my ak-74 to put it dead on at 25, I'm shooting at least 3 feet high at 125 yards.  now, I realize that the bullet is still "climbing"  at 25.  If i sight in at 100 then I'll be quite a bit low at 25 correct?  I'm shooting 3 gun and many of the targets are well under a hundred with a few at 100 or beyond.  makes we wish for a reticle with a center dot for 25 then tick marks above that for 75 and 100.  like a 556 reticle in reverse.  anyway, advise would be appreciated.  should i sight in at a longer range?  I know we used 25 meters to battlesight our weapons, but then flipped apetures and i believe there were in reality sighted in for 200 or 250.  Perhaps tha is my issue?  I feel like wih the red dot I am forced to pick a range at which I want to be accurate, and good luck with everything else.  Meanwhile my mak-90 with an iron peep site i'm consistently nailing bowling pins at 100 yards.......  help is appreciated.  I generally run the AK-74 or a ruger SR-556 for competition.

Yes you will be low at 25 yards with a 100 yard zero.  How much depends on your ammo, but we are talking inches, not feet.  The red dot should not be more burdensome to use than irons nor more "range specific" if you will.

What red dot are you using?  
Have you reconfirmed zero after having big inconsistencies with trajectory?
Are you sure of your mount?
Are you adjusting the intensity so the dot is reasonably visible?  This might be wide open for daylight, but you will get noticeable "blur" of the dot if the intensity is set too high for the amount of ambient light.
What ammo are you using?

I personally would not want a 100 yard zero for 3-gun, but others might.  Depending on your ammo choice, other shorter-ranged zeros will give you a tighter grouping over a wider range, but it is ammo dependent.

Pick one of he common AR zeros then just practice and learn your hold overs/unders.

When I was in the Army we used a target that was set up for the M16 or the M14.  We sighted in so that the top of our front sight was centered on the white box at the bottom center of a larger black quadrangle.  

If shooting the M14 we adjusted the sights so the bullets hit the X above the black quadrangle, if shooting the M16 we adjusted the sights so the bullets hit the X below the black quadrangle.

In other words, with the M16 the point of impact was below the point of aim at 25 meters.  Not point of impact being the same as point of aim.

If your red dot is arranged on the rifle so that you can co-witness with the iron sights I would think the point of impact would be about the same at 25 meters.  Or bullets striking below the point of aim.  I can't seem to get the file copied right now.  Photobucket isn't acting right.  It looks like the M16 POI is about 1.5" below the point of aim at 25 meters.  In those days we used 55 grain FMJ bullets.  I have no idea if the newer heavier/slower bullets are sighted in the same way these days or not.

Got it a different way.