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Old August 23, 2012, 09:33 PM   #1
jplacquay
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AR EOTech help please

Ok guys, I finally got my first AR. I bought a EOTech EXPS2-2 and have my G33 on order. My question is this. My local range is indoor and I LOVE it, but it only goes out to 25 yards. When indexed on the bullseye I know that at 25 yards the bullet hasn't had time/distance to rise to the level of the sight. So with that said I know the the impact on my target will be low at that range, how low should it be, if I want to be zeroed at 100 yards? Now, I do plan on hitting some outdoor ranges that will let me shoot from 50 out to 400 yards next week, its quite a drive for me though so I want to have some fun in the indoor range and get it as close as possible before I head to the outdoor range.




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Old August 23, 2012, 10:27 PM   #2
Gary L. Griffiths
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IIRC, if you zero about 1.5" low at 25 yds you'll be pretty much dead on at 100 yds.

OTOH, if you zero at 25 yds, you'll be about 1.75" high at 100 yds, and only about 1" low at 200 yds.

Assuming a 55-gr FMJ BT (M-193) bullet @ standard velocities.
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Old August 23, 2012, 10:44 PM   #3
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pretty much ditto what he said. i also have the XPS2-2. I sighted it so the center dot would be on target at 100 yards and the drop compensation dot is on target at my indoor ranges furhest extent, which is about 60-70 yards.
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Old August 23, 2012, 10:57 PM   #4
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Thanks guys! This really give me a good starting point.




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Old August 24, 2012, 07:26 AM   #5
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Quote:
When indexed on the bullseye I know that at 25 yards the bullet hasn't had time/distance to rise to the level of the sight.
Just as an aside.

Bullets don't rise.

They are falling from the moment they leave the barrel.

The "rise" you see is the face that the barrel is tilted up in relation to the Point of Aim of the sights. You are actually "lobbing" the bullet towards the target with a rainbow trajectory. Like an underhanded pitch. What you are doing is picking a point in the "lob" that hits where you want it to.

There will also be a 2nd point that the "lob" will cross your line of sight which varies based on the point that you have it 1st cross.

The very high sight line of the AR increases this effect.

This excellent post by Molon might help you understand it better.

http://www.m4carbine.net/showthread.php?t=65679
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Old August 25, 2012, 10:32 PM   #6
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Great point by Crow Hunter. Good thread fellows.
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Old August 25, 2012, 11:30 PM   #7
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OMG. That makes so much more sense than the way I e looked at it/been taught!!!!





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Old August 26, 2012, 12:19 AM   #8
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Any particular reason you want a 100 yard zero? As I understand it that sight is designed so that the top dot is zeroed at 50 and 200 yards, and the lower dot at 500 yards.
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Old August 26, 2012, 08:47 PM   #9
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I'm with the understanding the top dot is 0-300 yards and the bottom is 500 yards.





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Old August 27, 2012, 09:01 AM   #10
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It's whatever you zero the dot to, the question is what's the moa difference between the two dots (if I had to guess I'd go with 7.5 moa). Once you know that, when you set one of the dots zero to whatever range you want you'll then be able to calculate what the second dots zero will work out to. But nothing beats getting accurate dope at the range. Have fun.


jplacquay
What you may be thinking is what some refer to as battle sight zero. With the 5.56 round, using a 25M zero the round will land in an acceptable vital zone out to 300M. You'll be just under 4" high @150 and just under 2" low at 300

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Old August 27, 2012, 03:50 PM   #11
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from EoTech for a 25m zero

http://www.eotech-inc.com/documents/...ire_Target.pdf

The EoTech is 1/2" MOA at 100 yards

The dot is 1 MOA and the circle is 65 MOA
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Old August 27, 2012, 04:56 PM   #12
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The reason the military zeroes at 25 m is time and money. And it works because all of the rifles have the same barrel length, the same rifling and use the same ammunition.

Lord knows what you are using.

Shooting at 25 m will get you in the ball park. When you have the opportunity, go outside and shoot at 100 m, 200 m and 300 m to learn the trajectory of your weapon and adjust the sights to suit you with that weapon and ammunition.

The military weapon and ammunition is designed so that properly zeroed, you can aim at the center of a man sized target (E sized) anywhere from point blank to 300 m and expect to hit it somewhere. There is a range of zeros to do this. Pick what suits you.
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Old August 27, 2012, 05:45 PM   #13
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Quote:
Originally Posted by Crow Hunter View Post
Just as an aside.

Bullets don't rise.

They are falling from the moment they leave the barrel.

The "rise" you see is the face that the barrel is tilted up in relation to the Point of Aim of the sights. You are actually "lobbing" the bullet towards the target with a rainbow trajectory. Like an underhanded pitch. What you are doing is picking a point in the "lob" that hits where you want it to.

There will also be a 2nd point that the "lob" will cross your line of sight which varies based on the point that you have it 1st cross.

The very high sight line of the AR increases this effect.

This excellent post by Molon might help you understand it better.

http://www.m4carbine.net/showthread.php?t=65679
If we are picking nits, ALL bullets rise. It is physically impossible to fire a gun parallel to the ground. we live on a sphere, so the ground it always falling away from us in all directions.

Now, in practical application, all bullts are slowling down when they leave the barrel. Bullets have a parabolic flight path, and therefore do rise above the line of sight. Your description of a lob is essentially correct. And when fire a rifle at distance, the bore is ALMOST ALWAYS on some incline towards the target. This incline is of course determined by the distance to the target.


To the OP.... I have that exact same eotech..... If u dig out the manual it says to zero at 50yrds. this will get u on target with the top dot from 50-200yrds, bottom dot @500yrds, and bottom "T"of the circle @7yrds. Have fun


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Old August 27, 2012, 06:03 PM   #14
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Old August 27, 2012, 06:25 PM   #15
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Quote:
If we are picking nits, ALL bullets rise. It is physically impossible to fire a gun parallel to the ground. we live on a sphere, so the ground it always falling away from us in all directions.

Now, in practical application, all bullts are slowling down when they leave the barrel. Bullets have a parabolic flight path, and therefore do rise above the line of sight. Your description of a lob is essentially correct. And when fire a rifle at distance, the bore is ALMOST ALWAYS on some incline towards the target. This incline is of course determined by the distance to the target.


I think you need to do a bit more research.

Either that or you have inadvertently discovered the secret formula for the perpetual motion machine.



Seriously. Think about what you are saying. Gravity doesn't work on bullets but does on you? Do you rise as you walk forwards on a straight and level road?
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Old August 28, 2012, 03:06 PM   #16
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I never even mentioned gravity, which of course does indeed effect everything. I was mearly pointing out that while gravity effects the bullet at all times it its NOT falling the instant it leaves the barrel.

There is upward climb in every shot. I mearly stated it is impossible to actually fire parallel to the ground. Don't put words in my mouth.

If there were not gravity then the bullet wouldn't travel in an arch. Think of the gun on a battleship. Do the shells begin to fall the second they leave the barrel..... no they climb hundreds of feet before hitting the target up to 26 miles away. The same thing happens with Every gunshot, just on a smaller scale.

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Old August 28, 2012, 03:57 PM   #17
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Quote:
I never even mentioned gravity, which of course does indeed effect everything. I was mearly pointing out that while gravity effects the bullet at all times it its NOT falling the instant it leaves the barrel. Why is it not falling?

There is upward climb in every shot. I mearly stated it is impossible to actually fire parallel to the ground. Don't put words in my mouth.

I didn't put words in your mouth. Please explain how a bullet "climbs". If bullets climb, why don't we make bullet shaped aircraft with no wings. By your "hypothesis" if you put enough thrust on it, it will just start climbing, right? Why bother with adding wings?

If there were not gravity then the bullet wouldn't travel in an arch. Think of the gun on a battleship. Do the shells begin to fall the second they leave the barrel..... no they climb hundreds of feet before hitting the target up to 26 miles away. The same thing happens with Every gunshot, just on a smaller scale.

You are right, if there was no gravity, they wouldn't travel in an arch. They would travel in a straight line right out of the barrel. Just like a laser beam (which has no mass and is not affected by gravity, well except for black holes). They have to be fired in an arc because if you didn't they would hit the ground at the same time as a bullet dropped out of your hand at the same height. They climb because of the elevation of the gun, not because the bullet themselves "climb". They are all falling the minute they leave the barrel of a gun. This has been a well known fact for centuries.

Seriously man. This is basic physics.

There is no upwards climb. Please explain the physics behind why a bullet will climb?

Bullets are symmetrical why do they go up and not right or left?

Do bullets magically know which way is up?

I think you are getting confused about the word "fall". Falling doesn't mean that they are physically "falling" below your line of sight. It means that they will never be any higher than the straight line that your barrel creates. It will follow that line for a short distance then it will start to drop below that line until it hits the ground.

Look at the illustration that RamItOne posted. The bullet is not "falling" until it reaches the top of the parabola. However, relative to the bore axis, it is always falling. Because, with no gravity, the projectile would continue on following the axis of the barrel, it is "falling" away from the no gravity path and thus is considered to be falling from the time it leaves the barrel. But it doesn't have anything to do with the curvature of the earth or whether the round is slowing down or not. It is all just gravity.

http://www.physicsclassroom.com/class/vectors/u3l2a.cfm
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Last edited by Crow Hunter; August 28, 2012 at 05:41 PM.
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Old August 28, 2012, 04:02 PM   #18
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The moment the bullet leaves the barrel it is accelerating towards the center of the earth - otherwise known as down. It may have an upward component of velocity (getting higher or further away from the ground) but it is still accelerating down.

Using words like falling aren't precise. The colorful diagram above is correct. The trajectory - with respect to the line of sight - goes up, crosses the line of sight, reaches a peak, and then arcs down until it crosses the line of sight again. At all points on the trajectory, the bullet is accelerating downward at 32 feet per second squared.

There are some other less important forces which cause other accelerations. However, until we master gravity there isn't any point in discussing them.
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Old August 28, 2012, 06:13 PM   #19
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At this point, crow hunter, u and i are arguing the same point with different terminology.

I never said the bullets have lift, i was explaining the bullet does indeed RISE above the line of sight. as evidanced by every ballistic table known.... The bullet crosses the zero point(line of sight) at TWO DIFFERENT points. in the distance in between these points the bullet is ABOVE the line of sight.

Again a difference of terminology, the bullet does not begin to fall untill gravity can overcome the thrust imparted by the gunpowder. gravity is effecting it from the moment it leaves the barrel, but i wouldnt use the word falling until after the apex of the arced flight path. Yes gravity is pulling down on it, but gravity doesnt become greater than the upward thrust until the apex.

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Old August 28, 2012, 07:11 PM   #20
Crow Hunter
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Quote:
The "rise" you see is the face that the barrel is tilted up in relation to the Point of Aim of the sights. You are actually "lobbing" the bullet towards the target with a rainbow trajectory. Like an underhanded pitch. What you are doing is picking a point in the "lob" that hits where you want it to.

There will also be a 2nd point that the "lob" will cross your line of sight which varies based on the point that you have it 1st cross.
So what were you saying I was wrong about and trying to correct what I said?

You corrected me to agree with me?

Just through in some "interesting" facts about curvature of the Earth and bullets slowing down.

Glad we are on the same page now.

ETA:

Let me add an addendum to my statement before anyone picks anymore lice eggs.

Projectile speed and curvature of the Earth does have an effect on where the round actually hit, it doesn't have an effect on "falling" or the rate at which it accelerates "down".
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Last edited by Crow Hunter; August 29, 2012 at 06:50 AM. Reason: Clarification
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Old August 28, 2012, 10:19 PM   #21
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It was pointed out to me that 65MOA at 100 yards is about the height of the average individual of 5 foot seven inches. Helps extrapolation.
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Old September 26, 2012, 07:07 PM   #22
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Wow....this is certainly a very cerebral thread! My brain is starting to cramp, so I'll be taking my leave right now to mix a cocktail.
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Old September 26, 2012, 10:29 PM   #23
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So much confusion just because of slightly different understandings of a single word

Which I will not contribute to.

But I will say that the OP wants to fire his rifle in a small indoor range.

My advice is to double up on the hearing protection, not let any pregnant women into the range, and have a flashlight for when the lightbulbs shatter

It'll be loud.

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Old September 27, 2012, 12:04 AM   #24
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On a much milder note, I am happy for the OP that he has an indoor range that allows rifle ammo. There are none in my county that do. Handgun calibers only.
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