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Old 06-05-2020, 09:17 AM
Mammoth Mammoth is offline
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Default Help understanding red Dot targeting

Hello all, I'm really confused about something and I'm hoping someone can explain In a way I can understand.

I'm looking to get a red Dot for my new ar. I've never used one before. I was looking at the EOtech website and they have a pic of targeting with it. It shows the center Dot is zeroed for 50 yards. But to shoot 7 yards you use the bottom mark. This is where I'm confused. Wouldn't that raise the barrel and shoot higher? I'll try and post a pic of the circle from the website.

In my mind this is how it works. If I'm hunting with a regular scope I have it zeroed at 200 yards. If the deer is 300 I use a bottom mark raising the barrel and shooting further. If the deer is 100 I use a upper mark lowering the barrel and shooting closer. Is that not how it works for red dots?

I'm trying to wrap my head around how using a lower mark for closer works. I think I'm just missing something.

Thanks in advance for any help or clarification you can offer.

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Old 06-05-2020, 10:04 AM
jjfitch jjfitch is offline
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Default POA/POI

Not sure why their sight detail is confusing.

I sight in my 55 grain, FMJ, 3150fps at 25 yards, POI/POA.

POI at 50 yards is a little high, 100 yards is less than 2 inches high, 200 yards is POA/POI, 300 yards is about 5 inches low. Hold up your hand with your fingers together. If your POA is the middle knuckle at 25 yards your POI will be between the tip of your middle finger and wrist out to 250 yards.

Consider the height above the bore of the dot. 2 inches!!??

Check out the ballistic chart at the Hornady web site. You'll notice similar numbers for most popular calibers.

Smiles,

Last edited by jjfitch; 06-05-2020 at 10:12 AM. Reason: Syntax
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Old 06-05-2020, 10:34 AM
RWJ RWJ is offline
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It is related to the ballistic arc of the bullet; with the gun zeroed at 50 yards, the first time the bullet crosses the line of sight is at that point. With the line of the bore 2 inches below the line of sight, it is lower and still on its way up to the line of sight at shorter distance. Beyond 50 yards, the bullet is actually above the line of sight, and re-crosses the line of sight near 200 yards.


Your deer rifle has a similar arc, but with a 200 yard zero, the bullet has risen above the line of sight already, and is recrossing at 200 yards, hence the need to hold higher for 300 yards, and lower at 100 yards.

Last edited by RWJ; 06-05-2020 at 10:47 AM.
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Old 06-05-2020, 12:57 PM
Mammoth Mammoth is offline
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Quote:
Originally Posted by RWJ View Post
It is related to the ballistic arc of the bullet; with the gun zeroed at 50 yards, the first time the bullet crosses the line of sight is at that point. With the line of the bore 2 inches below the line of sight, it is lower and still on its way up to the line of sight at shorter distance. Beyond 50 yards, the bullet is actually above the line of sight, and re-crosses the line of sight near 200 yards.


Your deer rifle has a similar arc, but with a 200 yard zero, the bullet has risen above the line of sight already, and is recrossing at 200 yards, hence the need to hold higher for 300 yards, and lower at 100 yards.
Thank you. This is exactly the explanation I needed. It makes sense now. I appreciate your help

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Old 06-05-2020, 01:10 PM
Big Cholla Big Cholla is offline
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[QUOTE=jjfitch;140795792]Not sure why their sight detail is confusing.

I sight in my 55 grain, FMJ, 3150fps at 25 yards, POI/POA.

Consider the height above the bore of the dot. 2 inches!!?? QUOTE]

Re: only your original question. The above partial quote is your explanation. The AR system has an extraordinary height above the bore for the line of sight of the sighting system. The EO Red Dot system might be just slightly higher yet. Any AR sighted in for a fair distance will shoot low at very close distances because of the sight system's location above the bore.

Last edited by Big Cholla; 06-05-2020 at 01:12 PM.
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Old 06-05-2020, 07:13 PM
WR Moore WR Moore is offline
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FWIW, EoTech has had their problems. Plus, you really don't need a complicated reticle. A 1 MOA dot can be problematical for many to see. 2-3 MOA is a good all around choice. Also, the brighter you crank the dot, the larger the apparent size.

Beyond that: if you do your primary zero (55 gr bullet) at 50 yards/meters the dot will be relatively small in MOA and if you get your bullet dead center you'll see the bullet impact near the top of the dot at 100 yards/meters, still within the dot at 200 yards/meters and out to about 225 yards. Always check your POA/POI at longer range because slight errors you don't see at 50 yards/meters will show up there.

Now, as pointed out above, at ranges less than 50 yards/meters your bullet will be below the dot. Up real close, maybe the 2 inches noted above. At about 25 yards/meters, about half that. In those cases you'll need to hold that much high.

People get all steamed up about getting complex reticles that they really don't need considering the effective range and trajectory of the .223 /5.56 x 45 mm cartridge.
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Old 06-06-2020, 04:04 PM
KidK KidK is offline
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I’m new to the AR rifle world and had the same question. It wasn’t till I read this article that I realized the barrel angle is different than the optic angle.
How To Zero Your AR15 Rifle
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