Why does the ZERO on a rifle change so much in a year?

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post 22 explained it. CHANGING light conditions can easily move your POI more than an inch. the light condition indoors is unlike any "in the real world" as you called it. Fluorescent light directly above your head is not like bright sun, is not like clouds, is not like dusk or dark.
give me a moment and i'll post some of my notes and take a pic of test targets to help you understand
 
Hmm, I have moved rifles from indoors to outdoors my entire life and never once experienced a zero shift due to lighting (or if following the list I gave, period). What you have sounds like a "personal problem".

Many times people incorrectly attribute the causes of their shooting problems. Sometimes they mistake one physical phenomenon for another, something it's an excuse for poor marksmanship.
 
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Here’s one of the target scraps hanging on my wall. With gun zeroed in a sunny day when the sun was still fairly high in late afternoon. As the sun went below the trees my POI climbed .2. I dialed down .2 to confirm.

When I shoot in the evening and with nv I always shoot high and dial down to correct. The higher the sun, the lower my impact.

In high power they say “lights up sights up”. There’s a reason.

Clouds rolling across Casting shadows has a similar effect. Go watch a high power match on a partly cloudy day and you will see everyone shooting great in the sun and then a cloud goes overhead and suddenly everyone down the line is shooting a high 10 or 9.


For my part, if I have time I’ll zero only on a sunny day. If I have to zero when it’s cloudy I make a note.
 
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Are you claiming that this is a physical effect (that is, the sunlight changes the angle at which the bullet leaves the rifle relative to the scope or the subsequent trajectory) or an optical effect (the path the photons take from the target to the scope reticle changes)?

I find the first unlikely and the second will win you a Nobel prize if you can prove it.
 
I'd look at the following potential issues:

1) A loose screw somewhere in your mount.

2) Ammo variations.

3) Temperature variations.

What you're describing shouldn't be happening. A high dollar optic properly mounted on a gun with the same ammo in the same conditions should stay consistent.
 
Something I want to point out is we are talking about a 22 hornet. It’s been my experience that moderate velocity calibers like these move point of impact a lot with different loads and velocity changes. Much more so than high velocity cartridges like say a 30-06 or 243 ect...
 
Optical. Just like mirage the target isn’t where it appears to be.

It’s well known among high power shooters. It was the topic of much discussion in the PRS a few years ago.
 
Optical. Just like mirage the target isn’t where it appears to be.

It’s well known among high power shooters. It was the topic of much discussion in the PRS a few years ago.

Many things that are "well known" are also not true.

So let's take the rifle out of it. Mount a scope on a solid mount, and aim it at a target. Place a video camera behind the scope, showing through the scope how the reticle is aligned on target. Are you claiming that you can shine a light on the scope, the target, or anywhere in between and get the target to actually move with respect to the reticle in the camera image? You're claiming .2 mils of movement, so this should be visually obvious in the camera image. And you think you can do this without some sort of thermal effect that bends the scope or mount or causes the air to move?

I guarantee if you can do that, you will spark a revolution in physics leading to a Nobel prize for both you and whoever explains why it happens.
 
A friend of mine who works for a scope company did just that several years ago. He took a time lapse video over several hours through a scope. I watched the video several times. The reticle moved quite a bit through the day.
 
And your claim is that it's because of the light, and not simply mechanical movement due to heating of the scope or mount in the sun or a less than rigid mount? In other words that light itself acts as a lens for other light even in the absence of relativistic effects?

Seriously, if you can prove it you will receive a sizable chunk of cash from the Swedes. But exceptional claims require exceptional proof.
 
One easy way to tell heating from light: don't get the light from the sun. Do it indoors and just use a high output light and if you turn it on and the target moves instantly rather than over time, it's really due to the light.

Alternately you could heat the scope with a hairdryer without changing the light and see what happens.
 
Of course, this isn't nearly as interesting if the claim is that air at different temps is acting as a lens. We know that happens - it's all mirage is.
 
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Light does lots of interesting things. This photo is a good example.

But yeah. I’m saying the direction/amount of light sometimes makes a difference. Nothing to do with heat on scope which in my experience has never changed POI
 
And you're not talking about mirage due to air temp changes moving the target visually up (which is completely possible if you have layers of air at different temps - most common over water or on roads)?
 
I am only interested in hunting rifles so my comments are about hunting rifles. I have both tightly bedded rifle barrels and free floating barrels and for practical purposes they both shoot and maintain a zero about the same. The most change I see from year to year and from season to season is about one minute of angle. I have had rifles that I sighted in and with the same batch of powder and the same batch of bullets that I didn't have to adjust the zero for many years. One particular Mauser 25-06 that I owned went for almost 20 years using 120 grain Speer HotCor bullets and 49 grains of IMR 4831 without a zero adjustment. Most of the accuracy of a rifle is in the barrel itself and if you have a good barrel that is properly bedded it will maintain the zero, again within about one MOA from season to season and temperature to temperature.

When people go to the range each fall to "sight in their rifles" what they are really doing is not to sight in the rifle it's to see if they can still shoot the rifle as it was previously sight in. They change the zero to match what they are currently seeing. Changes in clothing, eyeglasses, the tilt of the rifle and how they see the scope picture all affect where the bullet is hitting. Some people who shoot prone don't get the same point of impact as they do when they shoot upright and they don't realize this is happening.

I think for the hunter the hype about temperature sensitive powders is really overblown and they are a ploy to sell more powder. I have used powders that are not supposed to be as temperature sensitive but they don't seem to perform as well as the time tested powders. I shoot in temperatures from 15 to 80 degrees F and again the point of impact may change about one MOA at 200 meters from a temperature change. Reloader 17 and IMR 4350 are supposed to be temperature sensitive and they are my favorite powders but I have never been concerned about the point of impact as temperatures go up and down. Most of my rifles in four different calibers shoot about 2900 fps. Wind is far more of a problem than temperature change.
 
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I agree sage. I shot out many barrels of 260ai in matches with r17 and iirc for me it changed about 1.7 FPS per degree F. That never changed my zero but it for sure changed my velocity and at 400+ yards If I went from an 80 degree day to a 50 degree day I’d have to correct for that. From memory i think I use about .5 FPS per degree F for the “insensitive” H4350. I never changed my 100 yard zero because of it though
 
I agree sage. I shot out many barrels of 260ai in matches with r17 and iirc for me it changed about 1.7 FPS per degree F. That never changed my zero but it for sure changed my velocity and at 400+ yards If I went from an 80 degree day to a 50 degree day I’d have to correct for that. From memory i think I use about .5 FPS per degree F for the “insensitive” H4350. I never changed my 100 yard zero because of it though

Punch in your velocity numbers in a ballistic calculator for the temperature driven velocity differences and you will see why at 100 yards, velocity driven poi shift is typically not noticeable.
 
For now I will stay out of the factors for minuscule changes in perceived POA and final POI but will go back to the OP’s problem.

...if it goes a year it will move 5 inches. It will shoot almost any load with perfection, just needs to be checked often.

I am going to go out on a limb and make an assumption, being that the rifle is a .22 Hornet, he is talking about at 100 yards. 5 inches at 100 yards isn’t going to be caused because of lighting conditions, unless you just can’t see the target to aim at it.

I have seen changes from many things but if I have a rifle that will shoot even slightly less than perfect groups, the mechanical parts don’t change enough over time for “apple to apple” results to differ by that much.

The amount of change the OP is experiencing should make it fairly simple to find the cause, if focused on scientifically.

but maybe metal moves with storage like my friend says.

Having a decent optic, properly mounted change from set location by 5” without being impacted by something isn’t something I have seen often and I don’t know I have ever seen one move like that, rezeroed and everything is fine again until it goes unused for some period to repeat the process again.

Again we are talking about a rifles scope that’s 20 clicks off at 100 yards just because it hasn’t been used for 365 days.

If metals moved that much on their own, standards, measuring instruments and countless other things, couldn’t be made from metal.
 
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I am only interested in hunting rifles so my comments are about hunting rifles. I have both tightly bedded rifle barrels and free floating barrels and for practical purposes they both shoot and maintain a zero about the same. The most change I see from year to year and from season to season is about one minute of angle. I have had rifles that I sighted in and with the same batch of powder and the same batch of bullets that I didn't have to adjust the zero for many years. One particular Mauser 25-06 that I owned went for almost 20 years using 120 grain Speer HotCor bullets and 49 grains of IMR 4831 without a zero adjustment. Most of the accuracy of a rifle is in the barrel itself and if you have a good barrel that is properly bedded it will maintain the zero, again within about one MOA from season to season and temperature to temperature.

When people go to the range each fall to "sight in their rifles" what they are really doing is not to sight in the rifle it's to see if they can still shoot the rifle as it was previously sight in. They change the zero to match what they are currently seeing. Changes in clothing, eyeglasses, the tilt of the rifle and how they see the scope picture all affect where the bullet is hitting. Some people who shoot prone don't get the same point of impact as they do when they shoot upright and they don't realize this is happening.

I think for the hunter the hype about temperature sensitive powders is really overblown and they are a ploy to sell more powder. I have used powders that are not supposed to be as temperature sensitive but they don't seem to perform as well as the time tested powders. I shoot in temperatures from 15 to 80 degrees F and again the point of impact may change about one MOA at 200 meters from a temperature change. Reloader 17 and IMR 4350 are supposed to be temperature sensitive and they are my favorite powders but I have never been concerned about the point of impact as temperatures go up and down. Most of my rifles in four different calibers shoot about 2900 fps. Wind is far more of a problem than temperature change.

My father law has a Weatherby Vanguard sporter with a real nice high figure stock, not bedded or free floated in 270 that the scope caps never came off in 15 years. We always joked that if he ever did have to adjust it the caps would be rusted on. Sometimes a guy gets lucky! I agree with you on the temp sensitivity thing. For many rifle the velocity loss has little or no affect inside 200 yards or so. Some rifles however even 100 FPS loss is dramatic.
 
Like most mysteries in life, it’s probably the combination of multiple factors. Lighting isn’t 5”. But it could be 2”. And easily 1”. Scope adjustments especially parallax is probably worth another.

Many many tests have been done on impacts to the objective bell on zero and there are few of any pic rings that will not shift a bit. Maybe riding around in his truck to the range or however he stored it could be worth another inch.

All we can do is speculate on the possible causes which were pretty much done on the first page.
 
I agree sage. I shot out many barrels of 260ai in matches with r17 and iirc for me it changed about 1.7 FPS per degree F.

Those of us who have used rifles for many years think about all kinds of scenarios to get better performance out of a rifle. What I have done to reduce the affect of temperature on rifle powder is to sight my hunting rifles to point of impact when the temperature is about 50 degrees. By doing this using taliv's example for Reloader 17 is to accept a maximum 50 fps reduction in velocity at 20 degrees and a maximum 50 fps increase in velocity at 80 degrees. A maximum change in velocity of 50 fps from 20 to 80 degrees is not material for a high speed bullet in hunting situations out to 200 meters, or even further. Since most of the deer hunting in my area is at temperatures between 35 and 60 degrees the maximum velocity change by temperature is only about 25 fps. With R 17 a standard deviation in velocity of about 10 fps also has a minimum affect.
 
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The issue with temp sensitivity is not so much a change in drop as it is a change in barrel timing. There are exceptionally good reasons to use temp insensitive powders, and not using them is a big part of the reason high power guys are always complaing their zero moved. It's really pretty simple - there's a list of things you have to do to get a consistent zero. Do them, you get one. Don't do them, you may not and are depending on luck.
 
i don't recall high power guys complaining about their zero moving. varget is one of the least sensitive powders and is by far the most popular in HP. not sure what HP you hang out with
 
I would wonder what percentage of hunting rifle barrels have been clocked. Very few I would guess. The manufacturers who produce hunting rifles have enough problems with quality control and cost without expecting them to clock every rifle barrel. If you went to the precision long range rifle group who are very serious about long range accuracy you would find more but their rifles are expensive and unfamiliar to the general public.

It's not difficult to get a quality hunting rifle to shoot minute of angle groups. To get a rifle to shoot half minute groups takes a lot of money and I don't go there.
 
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i don't recall high power guys complaining about their zero moving. varget is one of the least sensitive powders and is by far the most popular in HP. not sure what HP you hang out with

Light sure makes a zero difference with iron sights!

As for complaining about zero moving, I always heard HP shooters complaining about zero changes during leg matches at Perry. If politics could have entered into zero changes, they probably would have blamed that. As you probably know, no sighters during leg matches.

Based on the number of matches I have shot at different ranges across the country, particularly smallbore prone, zero's for hand held rifles seem to be always slightly different at different ranges. I believe this has to do with the differing heights between firing points and targets. Moving your elbow and cheek up and down, because the target is a little higher or lower, relative to your position, I believe it does change zero's. Everything affects everything.
 
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