i'm shooting a rem. 700 in 30 06 ,i have leupold standard bases. i'm dead on at 100,and 200 yds but 2" left at 300 yds. is there an explanation for this? could i need to adjust the rear mount, and recenter the cross hairs ? would that make a difference ?

Don,
 
Lets keep it simple.........I presume your scope has 1/4 minute clicks..so the quick and easy way is to do 2 clicks right.  This will move your point of impact at 300 yards 1 and 1/2 inches right---it will move your point of impact 1/2 inch right at 100 yards.  For all intents and purposes, you will be good to go at 100,200 and 300 yards.  
 
Ol' John

What John says is a fine place to start mechanically, but as stated, the way you put things violates the laws governing projectile motion.
 
There is no constant force working on the bullet after it leaves the bbl except gravity. Of course wind can exert a force, but from range session to range session, this force is random both in magnitude and angle. Therefore, unless the wind always blows from right-to-left at your range, "something else" is up.
 
What I suspect is "up" is that you're not as "right on" at 100 and 200 as you think. If you'll post your 100, 200 and 300 yd targets, (or e-mail images of them to me), I'll calculate the "center-of-mass" of each group. What I suspect we will see, is that you are just a "shade" right at 100, right "on" at 200, and maybe not as far as 2" left at 300.
 
300 yards is a long range when it comes to putting your bullets exactly where you want them. Lotsa folks say "My rifle shoots 3" groups at 300 yds." What they don't say is that the 3" group was not on the bull's eye, nor at the predicted drop directly below the bull's eye for 300 yds. Group size is all they report. Personally, 2" left of Point of Aim at 300 yds ain't too shabby unless you're competing. If you're competing, 2 inches left at 300 isn't even "in the ballpark".
 
But your mileage may vary.
 
Paul

My first thought would be wind.  If its not that than as Paul said....also another thought is regarding your shooting technique.  Do you have a good solid rest?  How is your sight alignment and picture?

Wind, Parallax and practice come into mind. Most scopes are set at 100 yards for parallax....the wind can move bullets alot more than people think. Practice is the most important. Also practice at 400 and the 300 becomes alot easier! Then practice at 500 and.....well you get the picture. Regards, Rick.

thank you guys those are some very good thoughts. i think you're correct,2 clicks right would make the difference at 300. i hadn't even thought about the effect of 2 clicks at that distance.  i'm only shooting at that range to see exactly what it's doing there. it's quite interesting . again thank you very much for your help

LOL  Guys, unless im missing something obvious, the question should also be are you canting the rifle at all? Hes not that far off, a cant would do exactly what he's talking about at 300 yds, but wouldnt be as obvious at closer ranges.

Paralax- a Leupold rep gave me the skinny on that once, he said even with a very miss adjusted ocular lens, that farthest an otherwise functioning scope would be off target is 2 inches at 500 yds, its not really a problem for all intents and puposes.

azhdryder, i don't think i was canting the rifle, i'm quite caeful about that. i haven't shot since that post but i think the 3 click adjustment just might work. thanks for the idea.
don