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Optics, Mounts, Rails and Sights If it aims your firearm, post about it here.

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  #1  
Old 02-24-2013, 7:45 AM
moger moger is offline
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Default distance to zero scope/ and how to calculate distance.

is there a standard distance to zero a rifle scope? i'm guessing 100 yards and from there u make adjustments at 200, 300 and so on. and write down what adjustments u made at each yard so u have reference sheet to go by... but idk,,
also i been looking online how to calculate the distance using your scope.. i kinda got it down using mildot.. but what about EBR-1 MRAD? u would u calculate the distance with that reticle?

can someone school me on this or tell me where i can find this info
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Old 02-24-2013, 8:50 AM
rero360 rero360 is offline
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Just like any other Mil based reticle, MRAD stands for milliradian or simply Mil. Now I'm going under the assumption that your scope has a first focal plane reticle, in which case its easy: look thru the scope at the target and determine how big it appears, the finer subtensions in the reticle help you be more precise. distance of target is height of target (or width) * 25.4 / target size in mils = distance in Meters. For yards its the same formula only use 27.77 instead of 25.4

As to distance you want it zeroed, that is entirely up to you, caliber using and what you intend to use it for. for example, my .308 is currently zeroed at 100 (I think, been far too long since I took it out) but my AR has different zeroes depending on the sighting source, irons and Micro T1 are zeroed at 100 yards, ACOG is set so its all matched up (zeroed at 100 and then refined at 300) And the USO variable will be zeroed at 300 meters (will be on my work gun) once I get my new rings.

Basically, once you determine what you want to do with it, take a look at a ballistic chart for your ammo, I like using JBM Ballistics, and figure out where an ideal zero for you would be.
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Old 02-24-2013, 8:50 AM
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It depends on the type of shooting that you'll be doing.

On my long range rifles I have a 100 yard zero and drop charts in 25 or 50 yard increments out to the maximum range of the rifle.

On my hunting rifles I have my zeroes based on the anticipated distances that I'll be shooting:
On my 375 H&H the zero is at 100 yards and I know the holdover for 200 and 300 yards.
My 7 Rem Mag is set up with a 225 yard zero so I can shoot out to 300 yards without holdover.
Each of my hunting guns is set up for a different target size and anticipated distance so the zeroes will vary.

Every type of reticle is going to be different, you are going to have to know the anticipated size of your target and how much any divisions in your reticle subtends at each distance.
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Old 02-24-2013, 10:07 AM
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Depends on what your normal distance will be, your caliber and your ammo.

What rifle?
What ammo?
Whats your typical range to target...or atleast whats your skill ability.

Don't mix possible with probable or capable with capability. My 16" .223 is capable of 400 yard accuracy, but the probability of my needing to do that is extremely low and my capability to successfully hit a target at 400+ yards with it out in the field without a bench and sandbags is nearly zero%.

I once saw a guys range book that had dope data out to 2500 yards...for his 5.56???

I would NEVER shoot at game over 200 yards away with a .223 with a Red Dot. I had my RDS zerod at 25 yards to have a cross zero at 375 yards. This was for human threats at that distance. I new to adjust my hold over/hold under when needed if the need existed. The close range zero was fine for game.

Now that I have a scope, I zerod at 50 yards which gives me a flat trajectory out to 200 yards, but at the cost of an extremely poor trajectory at 450 yards. At that point I would need to adjust the elevation as well as windage.

I am using a non-BDC reticule, but I worked out the sizes for each distance using my inner circle. You can see what I did with my reticule in this thread..http://www.calguns.net/calgunforum/s...d.php?t=690418 So looking at a known sized target I can guesimate the range and also think about what my trajectory will be like.

You would need to research and work this out for your specific reticule and ammo.
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Old 02-24-2013, 1:40 PM
moger moger is offline
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thanks.. i havent taken my rifle out to shoot yet..waiting on my scope.. wanted to know whats a good starting point.. so that when i take out to shoot.. i can have a better idea on what im doin as far as zeroin and calculating at different distance.. instead of wasting lot of ammo before i get it right..

oh also i plan on doin long range target shooting..
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Old 02-24-2013, 5:38 PM
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As mentioned before, what caliber? What bullet weight? You also need to know velocity at muzzle and bullets BC (ballistic coefficient) to determine it velocity loss as it traverses distance. The velocity loss determines it's drop across path. Velocity loss is controlled by drag coefficient, BC describes this.

Below are ballistics calculations (using RSI shooting labs software) for 55gr, 69gr and 77gr bullets in .223. You also want to know what centerline of scope to centerline of bore measurement is as this can greatly effect downrange path if you don't calculate for it.



To start with getting a zero, get it dead on at 50 yards, this will put it a tad high at 100 yards and kinda close at 200 yards. Then decide on what your final zero will be and refine it to dead on at that distance. Then use ballistics calculations for THAT specific bullet, velocity and sight height over bore to determine where bullet will be at points along it's path.

From there on you use hold over/under to get your hits, OR crank the proper dope onto the scope OR use reticule calibrations to determine aim point you use.

Best thing to do to start is to determine what "point blank zero" (PBZ) you want to use. A PBZ is set by picking the best 2nd crossing point for that bullet (bullet crosses line of sight twice, once as it climbs from muzzle (typically around 40-60 yards depending on several factors) and then again on it's way down. For 55gr .223 I like a 250 yard PBZ. This means bullet is never more than 2.5 inches above or below line of sight out to that distance and is dead on at 200 yards. This allows you to make minimal corrections if any at all through that range, then go to hold-overs beyond that.

BTW, altitude (air density) and humidity (to a degree) also effect path. Up or down angle you shoot at will also change drop across path.

Hope this helps you understand the process a bit more.

Last edited by GeoffLinder; 02-24-2013 at 5:42 PM..
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Old 02-24-2013, 7:44 PM
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Like guys mentioned fps,BC,humidity,pressure,temp,Coliolis,spin drift,LOS,and blah blah a few other factors that I don't feel like typing out lol.
To get you started 0 at 100 at 200 most calibers will drop about 2" and at 300 your first mill.

This will get you started but do your homework.

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Last edited by PrimaryArms; 02-24-2013 at 8:12 PM..
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Old 02-25-2013, 8:52 AM
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thanks guys,, and if matters..i would be shooting a .308 and as far as bullet weight goes..im gonna be shooting whatever rounds i can get my hands on around here..so its gonna vary..
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Old 02-25-2013, 10:41 AM
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Quote:
Originally Posted by moger View Post
thanks guys,, and if matters..i would be shooting a .308 and as far as bullet weight goes..im gonna be shooting whatever rounds i can get my hands on around here..so its gonna vary..
Each different bullet weight and mfgr batch of ammo will provide different results so you must test each one. Assumptions will not work.

With factory ammo you have no solid data on velocity in your rifle until you test that so nothing but actual testing for actual point of impact at the specific distances you want to shoot at will work. Mfgr. published velocities will not be the same in different rifles.

OR you can chronograph test the ammo in your gun to get the velocity, get Mfgr's bullet BC and then run a calculation. This will give you solid data on point of impact at ranges other than the range (distance) you initially zero at.

All this is relatively inconsequential at 100-200 yards but makes a huge difference at 400+ yards.
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Old 02-25-2013, 3:25 PM
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Quote:
Originally Posted by GeoffLinder View Post
Each different bullet weight and mfgr batch of ammo will provide different results so you must test each one. Assumptions will not work.

With factory ammo you have no solid data on velocity in your rifle until you test that so nothing but actual testing for actual point of impact at the specific distances you want to shoot at will work. Mfgr. published velocities will not be the same in different rifles.

OR you can chronograph test the ammo in your gun to get the velocity, get Mfgr's bullet BC and then run a calculation. This will give you solid data on point of impact at ranges other than the range (distance) you initially zero at.

All this is relatively inconsequential at 100-200 yards but makes a huge difference at 400+ yards.
"Assumptions will not work"
+1

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Old 02-25-2013, 3:29 PM
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Always zero optics at the range you plan on shooting. If you plan on shooting at multiple distances, you'll have to experiment a little and find out what works best for you with the given rifle, optics and distances.
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Old 02-25-2013, 4:06 PM
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maximum point blank range
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Old 02-25-2013, 5:18 PM
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Make your life easy, zero at 50 or 100 yards and run your calculations or your software from those zeros. My guess is you're shooting 223 or 308.

Do NOT zero at 25 yards. You probably should not consider zeroing at 200-300 yards until you're a very capable shooter so stick with 50-100 yards.
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Last edited by HK Dave; 02-25-2013 at 5:38 PM..
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Old 03-19-2013, 3:19 PM
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Zero at 100 and use a ballistics calculator such as iStrelok on your iPhone or Android phone. (assuming you have one) If you are going for precision shooting the ammo you put in your rifle will have a substantial difference in range, accuracy etc. Do some research on your particular rifle and round and there should be a lot of data on results. If you are taking precision rifle shooting seriously I'd consider getting a log book as well.
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Old 03-19-2013, 3:41 PM
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For 55/62 grain .223Rem zero at 35 and 300 yards, that will give you a 10" window from point blank to 350 yards.

Here is my point (top of triangle) of hold chart on the side of my rifles on a 10" diameter plate


Last edited by HighLander51; 03-19-2013 at 3:44 PM..
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Old 03-31-2013, 11:12 AM
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I have no idea of what your idea of "accuracy" is or "precision" is ,but most production rifles are capable of around MOA with match ammo. If MOA is what you seek, find a round that your rifle likes, AND STICK WITH IT! If you shoot every ammo under the sun...your gonna chase zero and you tail and be super frustrated.
If I can't get MOA or better with a bolt gun and match ammo...It's a looser in my book and getting sold.
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Old 03-31-2013, 12:41 PM
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Lots of complicated answers so I will give you a simple one. Go to an actual range that has a 50 yard line. Zero your scope in there. Now you're good for 200 yards. Anything less than that and your Point of Impact will be a little high. It should be dead on at 200 yards and a little lower the further out you go from 200. If you have a mildot try going to Nikon Hunting the website has a section for an application called spot-on. You input what your ammo, zero is and it tells you what each mildot is as far as range. It's really a cool application. If I' am not mistaken it even has an android or cell phone application.
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Last edited by negolien; 03-31-2013 at 12:44 PM..
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Old 03-31-2013, 2:33 PM
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Negolien, with all due respect, using your method is far from useful in exploiting the benefits of using the EBR 1 MRAD reticle, or any modern scope with a mil/moa reticle . My data shows a 175 grain SMK .308 at 2650 FPS dropping 3.8 inches at 200 yards when zeroed at 50. That is a lot of potential accuracy to give up in my opinion. Considering many systems are easily capable of MOA performance, why concede almost 4 inches at only 200 yards!
In the end, I guess it depends what the OP is after. Your method is probably within minute of deer.
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