zeroing distances and optics

[Kevatc]

I've been exploring the problems and pitfalls of a variety of zero distances for AR guns. For me I think what will work best is a 50 yard zero. Now this could be the dumbest question of the day but does an optic sight heigth above bore affect zeroing? My EoTech is co-witnessed so no prob there but what about an optic that sits higher?

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[Mark W.]

yes. You run into parallax error. Where the scope is actually pointed down relative to the bore line in order for the Point of Aim and the point of impact to coincide. Which if you have it sighted in at 50 yards will cause the point of aim to be way low at 100 yards etc.

Take a piece of paper and draw it out you will see what I mean.

http://www.eso.org/public/outreach/...eports-2004/rep-127/Figures/Fig(parallax).JPG
Parallax in Rifle Scopes

 

[jordanvraptor]

I use a 50 meter zero on most of my rifles. More because of the fact that its more convenient to use the 50 meter range than the 100. Still, I think its a good compromise for the calibers I use. Go here and play with the ballistics calculator. It has options for sight height and even crosswind.

Winchester Ammunition

 

[Kevatc]

yes. You run into parallax error. Where the scope is actually pointed down relative to the bore line in order for the Point of Aim and the point of impact to coincide. Which if you have it sighted in at 50 yards will cause the point of aim to be way low at 100 yards etc.

Take a piece of paper and draw it out you will see what I mean.

http://www.eso.org/public/outreach/...eports-2004/rep-127/Figures/Fig(parallax).JPG
Parallax in Rifle Scopes

Even if the red dot is "parallax free"?

 

[fd15k]

Even if the red dot is "parallax free"?

Yeah, Mark isn't talking about parallax - this is geometry and not optics. One must compensate for the height above bore with any type of sight: optic, iron, laser.

 

[fd15k]

Now this could be the dumbest question of the day but does an optic sight heigth above bore affect zeroing? My EoTech is co-witnessed so no prob there but what about an optic that sits higher?

There is no difference in zeroing. Regardless of how high or low is your sight, if it has enough adjustment, it can be zeroed at any distance. The problem really is in the fact that once you shoot at a distance other than your sighting distance, you may have to compensate wildly if your optics is way far.

For example, imagine you have optics sitting 4 inches above your bore (that is the distance between center of your bore and center of your reticle). Zeroed at 50 meters, that means your bullet will climb by 4 inches up before hitting your point of aim at 50 meters. Now if you shoot a target at 25 meters, you will be 2 inches low... which perhaps is not a problem. And what happens when you actually shoot at 100 meters with that zero ? Considering there will be almost no drop due too gravity at that distance in many rifle calibers, you will likely be 4 inches too high... that is a missed headshot

Now just by having the optics at 2 inches instead of 4 above the bore, described errors would also reduce by half.

 

[Flopsweat]

For a fun and practical application of this phenomenon, search for "AR battle zero". It's a way to be within a few inches of point of aim from 50 to 300 meters without adjusting the sights between shots. Or something like that.

 

[fd15k]

For a fun and practical application of this phenomenon, search for "AR battle zero". It's a way to be within a few inches of point of aim from 50 to 300 meters without adjusting the sights between shots. Or something like that.

Yes. Standard AR15 sights are about 2.2" above bore. Sighted at 50M it will be 2 inches too high at 100M, then due to gravity (check ballistic chart for given load / barrel length for exact numbers) it will drop some 2 inches and will be spot on at 200M, then it will drop a bit more, and will be some 2-3 inches low at 300M. All of that is negligible when aiming at center of mass.

 

[mkwerx]

Thanks for that link to the Winchester calc - I've got to sight my rifle in this weekend and that is going to help

 

[Kevatc]

For a fun and practical application of this phenomenon, search for "AR battle zero". It's a way to be within a few inches of point of aim from 50 to 300 meters without adjusting the sights between shots. Or something like that.

That is one zero I looked at but I decided on the improved battle zero because of the bullet trajectory from 25 -200+ yards is practical for me. For my eyes and EoTech I feel the "IBZ" is best for me. The reason I asked the original question is that I have noted different optics have greater bore to sight height distances. My gut said that this could have a impact on trajectory.

 

[wichaka]

For overall use, go with a 50 yard zero.

See Travis Haley video here, about AR zeroing;

Travis Haley - Adaptive Carbine: Zero at Distance - YouTube

 

[Kevatc]

For overall use, go with a 50 yard zero.

See Travis Haley video here, about AR zeroing;

Travis Haley - Adaptive Carbine: Zero at Distance - YouTube

That is why I chose the IBZ. This vid really does a good job in a short and sweet way of showing the pro's and con's of a given zero distance without promoting one distance over another.

 

[TapRackNGo]

For overall use, go with a 50 yard zero.

See Travis Haley video here, about AR zeroing;

Travis Haley - Adaptive Carbine: Zero at Distance - YouTube

Good vid, thanks for posting. I haven't seen that one before.

 

[Misterbill]

Sounds like this is a question about an optic sight mounted on a AR handrail?

OP, could you be more specific?

In general, your optic, which is sighted in at 50 yards will shoot at roughly the same POA at 200 yards. (Roughly). Every optic and every different rail adjusts a little bit differently. But finding and correcting the POA shouldn't be too much of an issue. \

If you're having specific problems, please state those specific problems, including the make of the rifle, the optic and where and how you're mounting said optic so we can be of more help.

Without that info it's very hard to diagnose a problem.

 

[Kevatc]

Sounds like this is a question about an optic sight mounted on a AR handrail?

OP, could you be more specific?

In general, your optic, which is sighted in at 50 yards will shoot at roughly the same POA at 200 yards. (Roughly). Every optic and every different rail adjusts a little bit differently. But finding and correcting the POA shouldn't be too much of an issue. \

If you're having specific problems, please state those specific problems, including the make of the rifle, the optic and where and how you're mounting said optic so we can be of more help.

Without that info it's very hard to diagnose a problem.

No problem as of yet. Going to be getting a 300 BLK upper and I wanted to put an optic on it. I would like to have the money to do either a Leupold 1-4x or a similar Vortex. As best as I can tell those have very similar sight to bore heights to the EoTech I already have. Then another person mentioned the Lucid HD7 which is a ACOG looking 1x red dot. The Lucid looks like it sets higher and so that was the basis of my question. fd15k had a good point which was the lower the optic the better. I guess when it comes to optics there is always a give and take in terms of zero issues.

To be honest, if I can shoot minute of milk jug at 200 yards with a 1x red dot I will be happy. Neither my 5.56 AR or the 300 BLK I hope to get in the near future will be (nor meant to be) "sniper reach out and touch someone" type guns. It's always fun to shoot milk jugs or pumkins at several hundred yards but the mission I have for these guns really will be 50 yards and less and likely under 25yards in a defensive scenario. Because of this I am finding it harder and harder to justify a $500 and up optic be it a 1-4x or EoTech or Aimpoint. That's why I looked at the HD7 and am looking at other red dots. However, as I wondered earlier in the thread would an optic that sits relatively higher have more issues with doing an IBZ zero. I know I could zero any optic to 50 yards but would the bullet strike roughly in the 200 yards POA or would it be off considerably due to the great sight to bore height difference?

 

[Misterbill]

No problem as of yet. Going to be getting a 300 BLK upper and I wanted to put an optic on it. I would like to have the money to do either a Leupold 1-4x or a similar Vortex. As best as I can tell those have very similar sight to bore heights to the EoTech I already have. Then another person mentioned the Lucid HD7 which is a ACOG looking 1x red dot. The Lucid looks like it sets higher and so that was the basis of my question. fd15k had a good point which was the lower the optic the better. I guess when it comes to optics there is always a give and take in terms of zero issues.

To be honest, if I can shoot minute of milk jug at 200 yards with a 1x red dot I will be happy. Neither my 5.56 AR or the 300 BLK I hope to get in the near future will be (nor meant to be) "sniper reach out and touch someone" type guns. It's always fun to shoot milk jugs or pumkins at several hundred yards but the mission I have for these guns really will be 50 yards and less and likely under 25yards in a defensive scenario. Because of this I am finding it harder and harder to justify a $500 and up optic be it a 1-4x or EoTech or Aimpoint. That's why I looked at the HD7 and am looking at other red dots. However, as I wondered earlier in the thread would an optic that sits relatively higher have more issues with doing an IBZ zero. I know I could zero any optic to 50 yards but would the bullet strike roughly in the 200 yards POA or would it be off considerably due to the great sight to bore height difference?

Go with a Bushnell HoloSight. $250 or less and you're MOA accracy up to 400 yards.

I have mine sighted in at 50- yards, which is close enough at 200 yards and at 5 yards (household length max) is an easy adjustment by Kentucky windage. (easily ascertainable by you at the range.

 

[Blitzkrieg]

I sight most centerfire rifle calibers in 2 inches high at 100 yards.. this is very much like a 50 yard zero but lets me dial in a bit more alignment, horizontally

With 5.56 and 7.62 NATO that gives you a dead on hold up to 300 yards on men and larger targets

 

[The Redpaw]

Sight height question:

When measuring for the height of your optics above barrel, do you measure to the middle of the scope?

 

[Flopsweat]

Yep, center to center. Unless you're shooting pretty far it won't matter if you're off by an eighth of an inch.

 

[Blitzkrieg]

Up close (under 10 yards or so) you aim a bit high due to the AR15 sight offset. This is only important for head shots or a barracaded opponent revealing little target, IMO

I cannot recommend this video package enough

http://www.amazon.com/Art-Tactical-Carbine-Volumn-Edition/dp/B001JEQPKK

excerpts

http://www.youtube.com/watch?v=Ye30b3TL5wI

http://www.youtube.com/watch?v=qrRFLDyiKOQ