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Posted: 1/26/2009 6:58:05 PM EDT
Hello everyone:

I posted a similar question a couple of months again and did not get a response.  Does anyone out there know of a good zero for a 16 inch .308 on a AR platform?  What I am looking for is a zeroing technique along the lines of the 50 yards zero for the 5.56 ARs and the 82 foot zero for the AKs.

I am currently zeroed at 50 yards.

Thank you!
Link Posted: 1/26/2009 7:45:42 PM EDT
[#1]
There are a lot of variables.

with a 100 yard zero, with 150gr ball ammo, assuming a BC of .35 and a MV of 2750 and a scope height of 2.78" above bore, you would be within 1" from 42 to 162 yards.

with a 50 yard zero, same ammo numbers, you are within 2" from 11 to 237 yards.  Think of it as more of a rainbow.  You will be dead on at 50 and 205, and 1.8" high in the middle between them.

There is no single answer.  Depends on how you want to shoot.  Its not a secret, its math.

With a 55 yard zero, same numbers, you would be within 1" from 33 to 200 yards, that would make you exactly 1.0" high in the middle.  Sounds like a secret squirrel method to me.

Go find a ballistic computer and a chronograph, and some BC charts and go crazy.
Link Posted: 1/27/2009 7:22:55 AM EDT
[#2]
Instead of asking someone where to zero, determine this for yourself and you are more likely to remember the specifics.

Here is what I mean.

The military doesn't have a standardized zero for the 7.62 like they do for the 5.56. Even at that the army differs from the marines.

Here is how to do it:  Make a list of the following:

1. Bullet weight you want to use.
2. Muzzle velocity
3. Ballistic Coefficient of the bullet
4. powder charge weight
5. And ask your self what you want to do with it.  Is it set up for CQB, Patrol or Long Range.  What type of sight system are you using? Scope, Red Dot or Irons?

Take this information and go to www.biggameinfo.com (ballistics calculatro) and plug in the numbers.  The program allows you to adjust the zero range.  Keep in mind that when they ask for zero they are not talking about the close one.  By adjusting the numbers you can move the zero back and forth so that you get your desired trajectory.  Try to keep the maximum rise and fall of the bullet within 4" of sight path.

By doing this yourself you will come away with a better understanding of ballistics and are more likely to retain the information.

Link Posted: 1/27/2009 7:44:38 AM EDT
[#3]
Google "ballistics calculator"
Here's one

Then plug in the info that is specific to your rifle, the cartridge you are shooting and your desired zero range. It will give you the close range sighting info you need to get you near to the bullseye at your desired zero range.
Link Posted: 1/27/2009 9:17:37 AM EDT
[#4]
Thanks everyone for their input.  I guess the 7.62 NATO is more complicated.  Here are the specifics.  My setup is a LAR-8 .308 AR with a NightForce 1-4x24 NXS CQB sight on a Larue SPR-E mount.  I just called Larue and they said the height was 1.5 at the center.

Here are the specifics of the load I will mostly be shooting:

1.  147-149 grain Aussie 1983 Mil Surp.
2.  From the research I have done it should go about 2500 fps. from a 16 inch.
3.  Don't have info on the coefficient.
4.  With the optic that I have I guess I will be shooting CQB, but mostly paper target bulleyes.
5.  My indoor range is limted to 50 yards.

Initially what I was looking for was a distance where I could zero for 100 yards and 200 yards at the 50 yard indoor range.  Thanks again for everyones help and any input is greatly appreciated.

Link Posted: 1/27/2009 9:43:38 AM EDT
[#5]
The LaRue height of 1.5" is height above the rail.  You need height above bore, which is another inch or so.   2.5" should be close enough.

Winchester 147gr FMJ bullets quote a BC of .391   The aussie stuff should be close.

using those numbers and 2500 FPS, lets see...


With a 50 yard zero, you are 1" high at 100, dead on again at 158yards, and 2.3" low at 200.   That sounds pretty good to me.


If you want a 100 yard zero, shoot for .5" low at 50.
If you want a 200 yard zero, shoot for .6" high at 50.

Link Posted: 1/27/2009 9:48:34 AM EDT
[#6]
I had my ap4 set 2 inches high with 150s at 50 yards with an est. 2550 fps. That gives me close to an 8 inch PBR out to about 300 yards. If I need anything more than that I have the wrong rifle setup IMO.

AL
Link Posted: 1/27/2009 10:19:48 AM EDT
[#7]
Sorry for the new guy question, but what does PBR stand for?

Link Posted: 1/27/2009 11:07:00 AM EDT
[#8]
Quoted:
Sorry for the new guy question, but what does PBR stand for?



Point Blank Range wiki

How far can you shoot and hit with out adjusting anything.  Depends on size of the target.

Sierra write up
Chuck Hawks
Link Posted: 1/27/2009 12:34:13 PM EDT
[#9]
Quoted:
Sorry for the new guy question, but what does PBR stand for?








Link Posted: 1/27/2009 2:16:31 PM EDT
[#10]
Thats pretty funny Biggiben.  Now if only I could hit that can at 300 yards that would be great.  I sure would not be wasting good beer IMHO.  

Thanks for everyones help and humor.


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