Zero Shift from day to day

[bgris]

Trying to pin point what is causing my zero to shift from any where from .1 to .2 Mils. I have been experiencing this from zeroing in the morning vs zeroing in the afternoon. I believe that its caused by heat soaking the scope but im not sure. So far i have tried different scopes (ZCO and Khales). Right now my gun is in a bedded MPA matrix pro.

The question i have is what is everyone seeing as far as zero shifts and whats normal?

 

[cwebster]

What's a mil? Never heard of that measurement

 

[WSnyder]

What's a mil? Never heard of that measurement

You serious Clark?

Milliradian - Wikipedia

en.wikipedia.org

 

[WSnyder]

zeroing in the morning vs zeroing in the afternoon

Mirage? To expand on that: Doing nothing else, no changes or adjustments after zeroing in the morning what impact change do you typically see in the afternoon? Is it consistent?

 

[cwebster]

You serious Clark?

Milliradian - Wikipedia

en.wikipedia.org

What would that be in thousandths of an inch?

 

[rijndael]

I would remove yourself from the equation and shoot it off a front rest / rear bag and see if it still wanders around.

 

[rijndael]

What would that be in thousandths of an inch?

Please take this to another thread.

 

[ShtrRdy]

if it was me shooting I would blame it on me.

A milliradian, (mil), is 3.6" at 100 yards

 

[Coyotefurharvester]

What type(purpose) rifle, cartridge and powder ?

 

[gunsandgunsmithing]

Trying to pin point what is causing my zero to shift from any where from .1 to .2 Mils. I have been experiencing this from zeroing in the morning vs zeroing in the afternoon. I believe that its caused by heat soaking the scope but im not sure. So far i have tried different scopes (ZCO and Khales). Right now my gun is in a bedded MPA matrix pro.

The question i have is what is everyone seeing as far as zero shifts and whats normal?

if it was me shooting I would blame it on me.

A milliradian, (mil), is 3.6" at 100 yards

So, .36-.72 inches? Got wind flags out? Are the groups opening in any particular direction with any consistency? Horizontal, diagonal, straight vertical, etc. Different lighting can create vertical and wind typically has a diagonal shape but how apparent depends on several factors. Very few conditions give absolute straight vertical or even straight horizontal. Diag from low left to high right is NOT generally wind from a rh twist bbl. Group pics might be of help.

 

[RGRobinett]

Think of air as THIN WATER, of varying density, thus, image refraction, or, "slow mirage"! RG

 

[AlNyhus]

Here's a good exercise to try.
In the morning, set the gun up stable...front rest or bipod and a rear bag. Adjust the scope to zero on a target with a dot in the center. Don't touch the gun. Walk away and come back in a few hours and without touching the gun, see where your reticle is in relation to where it was earlier. 100 yds is best but 50 will work..

 

[bgris]

The gun is a fully custom 6 dasher PRS rifle. All shot are from a front bipod and rear bag. the groups look the same roughly 3/8th of an inch. The also only move vertical theres usually no side to side movement.

My intial thinking is that the aluminum is heating up with the sun and the heat. But if thats the case you would think the scope would be effected

 

[nwmnbowhunter]

Very well known in archery that with different lighting, indoor vs outdoor, light from above- left- or right, overcast.... all of it changes the way you see your sight and target and will need to adjust daily for absolute precision.

 

[Jeff Porter]

Head position behind the scope and parallax setting differences will give you shifts in zero. The better shooter I became, the less my zeros wandered.

 

[SecondsCount]

Trying to pin point what is causing my zero to shift from any where from .1 to .2 Mils. I have been experiencing this from zeroing in the morning vs zeroing in the afternoon. I believe that its caused by heat soaking the scope but im not sure. So far i have tried different scopes (ZCO and Khales). Right now my gun is in a bedded MPA matrix pro.

The question i have is what is everyone seeing as far as zero shifts and whats normal?

What kind of material was use to bed the action to the stock?

I remember a post by Chad at Long Rifles a while ago talking about how chassis still need to be machined and bedded to the action.

 

[wkdickinson]

Lots of things can contribute to POI shift (often between shots), most having nothing to do with the rifle itself. That's why, most forms of competition allow some number of "sighting shots."

 

[gunsandgunsmithing]

Lots of possibilities, some way more likely than others and some, more expensive than others. Keep it simple and preferably cheap, and go down the list.
If straight vertical, I'd say lighting is most likely and free. Tune is definitely a possibility too. The rest setup and or sand settling or front bag being too hard. If truly STRAIGHT vertical wind is not very likely but you get to a point in accuracy where you can only shoot as good as the conditions. Definitely buy ormake some flags. Huge deal here. It really can not be overstated.
It MIGHT be mechanical but I doubt it and would just go down the list methodically before jumping to more complex or expensive fixes.

 

[Downhill]

In Across the Course there's an old saying; "Lights up, sights up. Light down, sights down". Sunlight can affect the apparent location of a target.

 

[snert]

I am no math hguy, and certainly not a gunsmith or even a scientist. But I do know this.

When shooting a certain farm (any summer weather over 75 degrees and full sun) in NY, out to 600 yards, my rule was:
9AM-Noon, use normal zero and click calulations on chart.
Noon...down three clicks from the chart
1 PM...down four to five clicks
2PM down 6 clicks
3PM down 3-4 clicks
4PM down 2 clicks
5PM and after, use regular zero.

It's the sun