Changing Zero

Travelor · Post by **Travelor** » Thu Aug 21, 2008 2:58 am

Normally when we first get to the range before a match, I check the "chicken zero" on our rifles for the day as I clean my rifles after each match. Usually I shoot a few shots to "warm" the barrel, but the guns start right off shooting very small groups.

I have noticed a 1 MOA change in zero from mornings to afternoons when checking zeros before a match and again between matches in the afternoon. The morning's zero's being 1 MOA lower than the afternoons. Our original assumption was changing temperatures. Honestly I need to start writing down the temp and humidity and where the "chicken zero" is at specific times to try to determine what is causing this.

Has anyone else noticed this and have an explanation?

George

Kevin6q · Post by **Kevin6q** » Thu Aug 21, 2008 5:09 am

My guess is the light has changed. The sun angle changes the way you see the target through the sights.

Innocent · Post by **Innocent** » Thu Aug 21, 2008 10:18 am

George,
Yes MOA changes with temperature, light, elevation and of course humidity (that can cause mirage). Talk with Tureau next time you see him about locking a rifle in a vice and shooting every 30 mins from sunrise to sunset...and the range of movement of the group.

Mary

Travelor · Post by **Travelor** » Thu Aug 21, 2008 12:54 pm

I understand about temperature and humidity, but I do not think light affects POA vs POI with a scope.

BlauBear · Post by **BlauBear** » Thu Aug 21, 2008 1:14 pm

Sure it does George! I'll look up the reference when I get home and post it, but I know Kitty can fill in the details.

Travelor · Post by **Travelor** » Fri Aug 22, 2008 8:11 am

Not saying it cannot affect POI, just saying I do not believe it affects a scope sighted gun.

But I am willing to learn.

Stay dry,
George

_Shorty · Post by **_Shorty** » Fri Aug 22, 2008 1:32 pm

Yeah, I'm a little confused as to how the angle of the light can possibly affect anything.

BlauBear · Post by **BlauBear** » Fri Aug 22, 2008 7:28 pm

This article is based on open sights, but still has relevent points:
http://www.washingtonbluerifles.com/KeysConsistency.htm

This article is more directly related:
http://www.targetshootingnz.co.nz/uploa ... 2_Pt_5.pdf.

As lighting conditions change variable amounts of light enter your eyes and cause the target to appear brighter or dimmer, light direction changes shadows and sharing... Variations in sunlight are more intense at the Benton range because when that place is bright, it's really, really bright.

deadeyeky · Post by **deadeyeky** » Fri Aug 22, 2008 9:54 pm

yup, i see it every time i practice in the afternoons, ill check my chickens zero, and by the time our practice match gets to turkeys(and the temp goes down a little) i hafta come up 1/2 moa or 3/4 moa from my original turkey and ram setting, if i start on turkeys i see the same thing when i get to chickens and pigs, happens to me every week.......

_Shorty · Post by **_Shorty** » Sat Aug 23, 2008 12:58 am

Yeah, I couldn't disagree more. Changing light does not change POI in any way whatsoever. The fact that some people have problems using their open sights depending on how light is falling on their open sights is completely irrelevant to our shooting silhouette with scopes. There are all kinds of other factors that can affect POI, but lighting most certainly isn't one of them, not for us. Move along.

Chattcatdaddy · Post by **Chattcatdaddy** » Sat Aug 23, 2008 3:05 am

As far as the POI changing throughout the day when using aperture sights. Isn`t that a result of the reaction of light on the front postand changing the your point of aim and not the ammunition being used?

BlauBear · Post by **BlauBear** » Sat Aug 23, 2008 5:48 am

Chattcatdaddy wrote:As far as the POI changing throughout the day when using aperture sights. Isn`t that a result of the reaction of light on the front postand changing the your point of aim and not the ammunition being used?

Right - light doesn't affect ammunition, but it does affect how we see the target by changing light and shadow on the target, and ambient light determines how much light our eyes receive. The effect is much more profound on aperture sights because of light and shadow on the front post or blade but it also affects scoped shooting.

_Shorty · Post by **_Shorty** » Sat Aug 23, 2008 3:00 pm

How do you figure?

BlauBear wrote:but it also affects scoped shooting.

BlauBear · Post by **BlauBear** » Sat Aug 23, 2008 5:50 pm

Why wouldn't it? It's a matter of how they eyes see and the brain interprets a target. Scopes don't magically compensate for shadow and glare.

_Shorty · Post by **_Shorty** » Sat Aug 23, 2008 11:18 pm

I suggest you go read what you told us to read. They're talking about how the light affects how you see the open sights.

Now, if you actually have problems seeing the targets through a scope as the light changes, well, that's your brain. I have absolutely no problem with it at all. As the light changes from early morning to mid-afternoon, I do not all of a sudden think the rams have shifted an inch. But you go right ahead and change your scope settings! I won't mind!

Changing Zero

Changing Zero

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Light