Moving a scope on the top of an ar15

[yeti rider]

If a move my scope back toward my eye one or two notches, how much does it affect the aim of the scope? Will it take much to re-zero it?

 

[gmcttr]

May or may not take a click or two to re-zero. Shouldn't be much.

 

[Bennettjh]

I wouldn't think it would be much but you'll definitely notice a difference I would bet.

 

[yeti rider]

Thanks folks!

 

[pblanc]

Depends on how accurately your Picatinny rail is milled onto the top of your upper receiver and how well the receiver axis aligns with the barrel. With some ARs the long axis of the Pic rail deviates sufficiently from the bore axis either horizontally or vertically that an adjustment in windage, elevation, or both will be required. I had to move a scope mount one rail slot forward on one AR that I was shooting at an event, and found that it required a windage adjustment of a couple of MOA afterwards.

If you make a big forward or back adjustment, I think it will be akin to lengthening or shortening your sight radius with iron sights. Since the bore axis is inclined relative to the sight axis, if you shorten the sight radius the angle of the bore to the sight axis gets a bit steeper. If you go back, it gets a bit less steep, so either way the near zero point will change. If I am wrong on that point someone please correct me.

 

[russc2542]

Depends on how accurately your Picatinny rail is milled onto the top of your upper receiver and how well the receiver axis aligns with the barrel. With some ARs the long axis of the Pic rail deviates sufficiently from the bore axis either horizontally or vertically that an adjustment in windage, elevation, or both will be required. I had to move a scope mount one rail slot forward on one AR that I was shooting at an event, and found that it required a windage adjustment of a couple of MOA afterwards.

If you make a big forward or back adjustment, I think it will be akin to lengthening or shortening your sight radius with iron sights. Since the bore axis is inclined relative to the sight axis, if you shorten the sight radius the angle of the bore to the sight axis gets a bit steeper. If you go back, it gets a bit less steep, so either way the near zero point will change. If I am wrong on that point someone please correct me.

kinda sorta but not really.
sight radius is the distance between the front and rear iron sights akin to the handle side of the lever, the other side of which is the POI/POA. Changing the sight radius changes the linear distance you move one end of the gun to achieve a certain radial distance (travel around the circumference vs degrees). Locating the scope forward or rearward does technically alter the ballistics but (assuming everything's lined up to start with) if you zero at 100 yds and move the scope rearward one notch, you're now zeroed at 99yds, 11 5/8". The problem is if everything isn't perfectly aligned to start with (flight path, bore, pic rail, rings, scope internals) but you can adjust it to zero, now you move something non-linearly you stack the tolerances. Hence the previous comments that it oughta be close but may need a few clicks.