AR Sponsor
Posted: 3/16/2014 12:12:20 PM EDT
| I have researched and have not been able to find any info on this specific question I have. I want to zero in a red dot or 3-9 scope at 50 yards because I like the ballistics of the 50 yard zero. Everyone just keeps saying do 100 yards but I want 50 yard zero, both my red dots and my scopes are mounted higher than my irons so my question is does my scope/red dot being HIGHER than my iron sights have a different trajectory compared to my 50 yard iron sight zero? My question is talking more along the lines of scope height being taller than my irons. If it dosent make sense let me know, ill try to explain better if I can. |
|
red dot mount height doesnt matter if it co witnessed with the irons. the red dot "dot" isnt stationary in the glass. It changes location due to eye location because its just a reflection. A scope crosshair is different because they are fixed in the glass.
That all said, the scope height shouldnt be an issue if its close to the iron height. if its off my 7mm, then its off by 7mm.. You should check your POI at range anyway, and not just assume the POI do to calculations from 50. |
|
It certainly does. Having a red dot at a different height than your sites, means you will still be on at your zero of course (provided they are zeroed at the same difference) but your hold over will be different. Very small difference though. I think the difference between 1/3 cowitness and absolute is .2 inches.
This is why every ballistic calculator takes into account height over bore. So 2.6" for a standard iron sight and 2.8 for lower third. |
|
Quoted:
geometry would dictate yes, interested to hear what the differences would be at different ranges. where's the math experts? I would think as well but im just not sure. lets say a carry handle mounted red dot or scope, if the irons are 50 yard zero and then i decide to zero my reddot/scope mounted on top of the carry handle at 50 will it have the same trajectory? i know the poa changed but im more thinking trajectory. no my scope is not mounted that much highter off my flat top. if i have to guess scope and red dot are 1/3 co witness sight, maybe slightly higher. |
|
Quoted:
It certainly does. Having a red dot at a different height than your sites, means you will still be on at your zero of course (provided they are zeroed at the same difference) but your hold over will be different. Very small difference though. I think the difference between 1/3 cowitness and absolute is .2 inches. This is why every ballistic calculator takes into account height over bore. not if the red dot is co-witnessed. they will be the same. If your RDS has a 7mm riser (1/3 lower) and you lower the dot 7mm inside the scope, then there is no difference. You cannot co witness a scope cross hair and iron sites, while sharing the same zero. |
|
Quoted:
I would think as well but im just not sure. lets say a carry handle mounted red dot or scope, if the irons are 50 yard zero and then i decide to zero my reddot/scope mounted on top of the carry handle at 50 will it have the same trajectory? i know the poa changed but im more thinking trajectory. no my scope is not mounted that much highter off my flat top. if i have to guess scope and red dot are 1/3 co witness sight, maybe slightly higher. Quoted:
Quoted:
geometry would dictate yes, interested to hear what the differences would be at different ranges. where's the math experts? I would think as well but im just not sure. lets say a carry handle mounted red dot or scope, if the irons are 50 yard zero and then i decide to zero my reddot/scope mounted on top of the carry handle at 50 will it have the same trajectory? i know the poa changed but im more thinking trajectory. no my scope is not mounted that much highter off my flat top. if i have to guess scope and red dot are 1/3 co witness sight, maybe slightly higher. Mounting it on the carry handle will be more than an inch difference so a very significant change. |
|
Quoted:
not if the red dot is co-witnessed. they will be the same. If your RDS has a 7mm riser (1/3 lower) and you lower the dot 7mm inside the scope, then there is no difference. You cannot co witness a scope cross hair and iron sites, while sharing the same zero. Quoted:
Quoted:
It certainly does. Having a red dot at a different height than your sites, means you will still be on at your zero of course (provided they are zeroed at the same difference) but your hold over will be different. Very small difference though. I think the difference between 1/3 cowitness and absolute is .2 inches. This is why every ballistic calculator takes into account height over bore. not if the red dot is co-witnessed. they will be the same. If your RDS has a 7mm riser (1/3 lower) and you lower the dot 7mm inside the scope, then there is no difference. You cannot co witness a scope cross hair and iron sites, while sharing the same zero. I am fairly certain they will, I don't believe that that is the way red dots work. All co-witness means is that you can see your sights through your optic. They are independent sighting systems. Regardless the .2 inches is minuscule. Try a ballistics calculator. |
|
Quoted:
not if the red dot is co-witnessed. they will be the same. If your RDS has a 7mm riser (1/3 lower) and you lower the dot 7mm inside the scope, then there is no difference. You cannot co witness a scope cross hair and iron sites, while sharing the same zero. Quoted:
Quoted:
It certainly does. Having a red dot at a different height than your sites, means you will still be on at your zero of course (provided they are zeroed at the same difference) but your hold over will be different. Very small difference though. I think the difference between 1/3 cowitness and absolute is .2 inches. This is why every ballistic calculator takes into account height over bore. not if the red dot is co-witnessed. they will be the same. If your RDS has a 7mm riser (1/3 lower) and you lower the dot 7mm inside the scope, then there is no difference. You cannot co witness a scope cross hair and iron sites, while sharing the same zero. why can't you? if there's room and eye relief isn't an issue, I don't see how this would not be possible. an RDS and irons have to be absolute co-witnessed in order to share the same POA/POI when zeroed at the same range, lower 1/3 would create a very small deviation. the aiming reticle of an RDS is fixed(obviously it can be adjusted), the reflexion is what moves with your eye(parallax free), otherwise you wouldn't be able to zero it. |
|
Iron sites. Height over bore 2.6
1/3 Cowitness height over bore 2.8 m855 ballistic co .304 Muzzle Velocity 2984 out of a 16 inch Weight 62 grain Both zeroed at 50. Red dot would be .5 inches higher at 200 yards Iron sights would be about an inch lower at 400 yards. So not much of a difference with co-witness but much more of a difference with iron sites on carry handle. Lets say your red dot now sat at 4 inches above the bore mounted to a carry handle (as opposed to the 2.6 with irons). At 200 yards the red dot would impact 4 inches or so higher than the irons At 400 yards the iron sights would impact 9 inches lower than the red dot. Still with both zeroed at 50 yards. But plug it into a calculator for yourself. The higher over the bore, the steeper the angle you are holding the weapon with the same zero. |
| I would think that the higher you optic/sight is above the bore, the bigger the difference there's going to be when shooting at something closer or further away from your zero compared to an optic or sight mounted closer to the bore. In other words, if the optic is higher than the sights, and both have a 50 yard zero, the sights would have better accuracy when shooting at something that's 25 or 75 yards away. I could be wrong, but that's been my understanding. |
|
I have my Aimpoints z'd @ 50/200 and co-witnessed with irons. My ARs with scopes are all z'd @ 100 and don't have buis. 1 scope is the XTR14 and has reticle hold-overs, the other 2 are mil/mil with turrets.
If I had a rds on a carry handle, I would zero the rds @ about 65/200 and have the irons set at the ibsz |
|
Quoted:
Iron sites. Height over bore 2.6 1/3 Cowitness height over bore 2.8 m855 ballistic co .304 Muzzle Velocity 2984 out of a 16 inch Weight 62 grain Both zeroed at 50. Red dot would be .5 inches higher at 200 yards Iron sights would be about an inch lower at 400 yards. So not much of a difference with co-witness but much more of a difference with iron sites on carry handle. Lets say your red dot now sat at 4 inches above the bore mounted to a carry handle (as opposed to the 2.6 with irons). At 200 yards the red dot would impact 4 inches or so higher than the irons At 400 yards the iron sights would impact 9 inches lower than the red dot. Still with both zeroed at 50 yards. But plug it into a calculator for yourself. The higher over the bore, the steeper the angle you are holding the weapon with the same zero. 2.8 is the center of the red dot optic over the bore. this does not mean that this is the exact distance of the red dot itself over bore. If the red dot is truly co witnessed with the iron sights, then the red dot "DOT" is 2.6 over bore. It is no longer in the center of the actual red dot sight. |
|
Quoted:
I am fairly certain they will, I don't believe that that is the way red dots work. All co-witness means is that you can see your sights through your optic. They are independent sighting systems. Regardless the .2 inches is minuscule. Try a ballistics calculator. Quoted:
Quoted:
Quoted:
It certainly does. Having a red dot at a different height than your sites, means you will still be on at your zero of course (provided they are zeroed at the same difference) but your hold over will be different. Very small difference though. I think the difference between 1/3 cowitness and absolute is .2 inches. This is why every ballistic calculator takes into account height over bore. not if the red dot is co-witnessed. they will be the same. If your RDS has a 7mm riser (1/3 lower) and you lower the dot 7mm inside the scope, then there is no difference. You cannot co witness a scope cross hair and iron sites, while sharing the same zero. I am fairly certain they will, I don't believe that that is the way red dots work. All co-witness means is that you can see your sights through your optic. They are independent sighting systems. Regardless the .2 inches is minuscule. Try a ballistics calculator. co-witness means your red dot lines up on the same plane as your rear and front sight. the red dot is placed between the two sights, and the only way it can line up is if its on the same plane. If it lines up on the same plane, then it has the same poa/poi. |
|
Quoted:
Absolute co-witness means your red dot lines up on the same plane as your rear and front sight. the red dot is placed between the two sights, and the only way it can line up is if its on the same plane. If it lines up on the same plane, then it has the same poa/poi. Quoted:
Quoted:
Quoted:
Quoted:
It certainly does. Having a red dot at a different height than your sites, means you will still be on at your zero of course (provided they are zeroed at the same difference) but your hold over will be different. Very small difference though. I think the difference between 1/3 cowitness and absolute is .2 inches. This is why every ballistic calculator takes into account height over bore. not if the red dot is co-witnessed. they will be the same. If your RDS has a 7mm riser (1/3 lower) and you lower the dot 7mm inside the scope, then there is no difference. You cannot co witness a scope cross hair and iron sites, while sharing the same zero. I am fairly certain they will, I don't believe that that is the way red dots work. All co-witness means is that you can see your sights through your optic. They are independent sighting systems. Regardless the .2 inches is minuscule. Try a ballistics calculator. Absolute co-witness means your red dot lines up on the same plane as your rear and front sight. the red dot is placed between the two sights, and the only way it can line up is if its on the same plane. If it lines up on the same plane, then it has the same poa/poi. lower third co-witness will put your RDS and irons at different height above bore and change POI when zeroed at the same distance. see ajacobs post. |
|
Quoted: 50 yard zero is a good zero for red dots. Hell, the EOTech manual specifically says to zero at 50. Your 3-9 however is probably better served at 100, though. This all depends on the ballistics. I have my varmint rig zeroed at 50 yards. Why? Because it offers the least amount of deviation from POA from 25-250 yards (the ranges I plan on shooting critters). Using a 100 yard zero with the same load produced twice the maximum deviation (instead of ~2.5+/- it was ~5.7+/-). For small game, the former is more appealing. So, it all depends on what you are wanting to hit. I also use a 50 yard zero with my irons, and it has performed VERY well for me out to 500 yards on steel and paper echo silhouette targets, as well as reduced silhouette targets at 500 yards. |
|
Quoted:
co-witness means your red dot lines up on the same plane as your rear and front sight. the red dot is placed between the two sights, and the only way it can line up is if its on the same plane. If it lines up on the same plane, then it has the same poa/poi. Quoted:
Quoted:
Quoted:
Quoted:
It certainly does. Having a red dot at a different height than your sites, means you will still be on at your zero of course (provided they are zeroed at the same difference) but your hold over will be different. Very small difference though. I think the difference between 1/3 cowitness and absolute is .2 inches. This is why every ballistic calculator takes into account height over bore. not if the red dot is co-witnessed. they will be the same. If your RDS has a 7mm riser (1/3 lower) and you lower the dot 7mm inside the scope, then there is no difference. You cannot co witness a scope cross hair and iron sites, while sharing the same zero. I am fairly certain they will, I don't believe that that is the way red dots work. All co-witness means is that you can see your sights through your optic. They are independent sighting systems. Regardless the .2 inches is minuscule. Try a ballistics calculator. co-witness means your red dot lines up on the same plane as your rear and front sight. the red dot is placed between the two sights, and the only way it can line up is if its on the same plane. If it lines up on the same plane, then it has the same poa/poi. It is a common misconception that the sights relashionship to each other matter for some type of co-witness. Co-witness only means you can use one set of sights through the other. When using one you totally disregard the other. The only purpose it serves is to allow you to use your irons through the optic when the optic goes down. The purpose of lower third is for people who find the optic cluttered either with the front or rear sight fixed or deployed. Raising the red dot optic so the irons areout of the way. The entire benefit of a red dot is that it does not have to be on some plane that is roughly parrell to the barrel. Being able to still use an optic with the dot drastically off center in the optic due to rapid acquisition, poor cheakweld or awkward firing positions. If what you say was true, there would be no point in having lower third mounts, because the dot would be equally obscured by the sight. |
|
Quoted: I have researched and have not been able to find any info on this specific question I have. I want to zero in a red dot or 3-9 scope at 50 yards because I like the ballistics of the 50 yard zero. Everyone just keeps saying do 100 yards but I want 50 yard zero, both my red dots and my scopes are mounted higher than my irons so my question is does my scope/red dot being HIGHER than my iron sights have a different trajectory compared to my 50 yard iron sight zero? My question is talking more along the lines of scope height being taller than my irons. If it dosent make sense let me know, ill try to explain better if I can. Then zero at 50. You are probably already a step ahead of most of those who recommend you a 100 yard zero; since it sounds like you've actually compared the ballistics. When I was looking at zeroing my 4.5-14x42, I was pretty much set on a 100 yard zero since that's what you see most people recommend on forums. Then I looked at several ballistics calculators, and saw that for MY NEEDS, the trajectory of my load using a 50 yard zero was much more appealing for hitting smaller game (i.e. groundhogs). Figure out what ammo you are planning on shooting the most, plug it into a ballistics calc, and determine the range you plan on shooting. This will give you your best zero range IMHO. |
|
Quoted: why can't you? if there's room and eye relief isn't an issue, I don't see how this would not be possible. an RDS and irons have to be absolute co-witnessed in order to share the same POA/POI when zeroed at the same range, lower 1/3 would create a very small deviation. the aiming reticle of an RDS is fixed(obviously it can be adjusted), the reflexion is what moves with your eye(parallax free), otherwise you wouldn't be able to zero it. Quoted: Quoted: Quoted: It certainly does. Having a red dot at a different height than your sites, means you will still be on at your zero of course (provided they are zeroed at the same difference) but your hold over will be different. Very small difference though. I think the difference between 1/3 cowitness and absolute is .2 inches. This is why every ballistic calculator takes into account height over bore. not if the red dot is co-witnessed. they will be the same. If your RDS has a 7mm riser (1/3 lower) and you lower the dot 7mm inside the scope, then there is no difference. You cannot co witness a scope cross hair and iron sites, while sharing the same zero. why can't you? if there's room and eye relief isn't an issue, I don't see how this would not be possible. an RDS and irons have to be absolute co-witnessed in order to share the same POA/POI when zeroed at the same range, lower 1/3 would create a very small deviation. the aiming reticle of an RDS is fixed(obviously it can be adjusted), the reflexion is what moves with your eye(parallax free), otherwise you wouldn't be able to zero it. Looking through a magnified scope puts the irons in a different focal plane. You would not be able to see them well if at all. At 3x or higher, you won't see them at all. Its not about the height, its about the magnification. This is not an issue with red dot sights that offer no magnification. |
AR Sponsor