Changing Zero

[Travelor]

The linkabove did not work. This one did.


http://www.targetshootingnz.co.nz/uploa ... 2_Pt_5.pdf

George

[steve b.]

it's temperature.

in rimfire benchrest, using my rail guns, i can watch the poi climb as the day becomes warmer.

i have not seen light influence this. the targets are posted at the same height, creating the same aiming point, and the rifle is on a rail, and it lines up within 1/8" or less card to card.

it's so predictable that i add in a few clicks after the second card (nightforce scope 12x42x56 BR), and have them noted. every time it's the same number of clicks.

not accounting for this change burns alot of rimfire benchrest shooters.

s.

[edgehit]

Steve B,

Would you say that the effect of temperature can invoke a full MOA of change? I know where I shoot the range temperature changes up to 20 degrees during a day.

My thinking is that the original poster may be experiencing some effect of stock pressure influencing POI brought on by temperature change or a change in how he's shooting technique off the bench.

[Innocent]

Steve,
Thanks for posting your comments, solar energy is so much fun. I wondered how long it would take for someone to add the comment about temp. I usually go by a basic rule of thumb that as the light gets brighter, the bullets go higher (the sun is warming the surrounding air mass). Not always true in Florida as there are times when a cold front comes through, and the initial overcast/rainy skies are warmer than the clear air mass behind the front that drops the temp by 20+ degrees F.

George,
Tureau will be at Mid South, if you will take the time he will talk with you, about his tests with a rail gun. Be prepared to ask a simple question and get a 60 page thesis defense answer, but it will be full of facts.

Edgehit,
Potentially a full minute of angle or more, we are not dealing with just one variable (temperature) in this equation, but rather dealing with one that can cause many changes in the other variables.

Innocent Mary

[steve b.]

yeah, i have really seen it here in the hot south west, and it would easily move 1 MOA, most likely more, but i have not tested it out to 100 yards.

sunny and increasing temps go hand in hand, and i guess i never looked at it that way. interesting, i will have to ponder that one for a while.

it's not uncommon to start a match in the high 70's and end the match in th elow 100'ds.

s.

[Travelor]

Come on guys, let's not let this thread die. I'm enjoying the differing opinons too much.

I still say that the light conditions do not affect the POI of a scope sighted rifle - I believe that they affect iron sights only.

[jneihouse]

Okay, just for fun let me throw this out....Do a google search on "how light affects what we see" and you'll turn up a bunch of scientific material that basically says this.....What we see is reflected light, not an actual object...hence when it is pitch black (such as deep in a cavern or a windowless room with no light) we can't see anything because no light is being reflected. Dim light we see dimly as less light if reflected. Reflected light is light bouncing off an object.....The angle of reflection changes relative to the position of the sun in the sky or due to diffusion if there is cloud cover....It's a given that the silhouette target does not move during the day...it is in a fixed position. Shooters move and the sun moves but the target stays in the same place...Is it possible that there is an optical illusion being caused by the movement of the sun across the sky in relationship to the target and the actual target is not where we think it is based on the reflected light from the target?? Remember it takes very little movement to move a bullet 1" at 100 meters...Would take very little change in perception to cause a perceived change in point of impact at 100 meters....I've shot sillhouettes on a lot of ranges from coast to coast all across the country and, probably more importantly to this discussion, been on the spotting scope for some very, very good shooters on these ranges in several different lighting conditions and there is a definite shift on some days in some conditions. It is much more pronounced on sunny days. I would agree that light does not affect optics the same way it does iron sights. But optics, being magnifiers and light gatherers, could magnify and enhance any perceived shift in light on the target.....

Just my thoughts, not trying to build an argument for one way or the other....Would like to hear Lone Ringer's thoughts on the matter, as well as other experience and accomplished spotters like Innocent Mary and Chris Winstead, all who have vast experience spotting and calling the shot for very, very good shooters in all types of conditions....

That ought to keep this thread alive for awhile.

Kitty

[_Shorty]

Heh, funny what some people will believe.

[BlauBear]

You need to listen, Shorty, you could learn something. John is a top notch spotter and sports photographer that speaks with authority. I'm always happy to challenge him, sometimes I live for testing his advice, but simply blowing him off is a mistake.

[_Shorty]

Sorry, but if you honestly think that the angle of the sun is going to change where a target appears to be to you, well...actually, I don't care if you believe it. Because you're not me. And you'll be adjusting your scope, and I'll be leaving mine on-target.

[Innocent]

Stable Gentlemen,
Sunlight, artificial light, shadows, and the optical nerves are all interesting subjects on their own. Years of photography, living in the weather, measuring sunlight (probably to a degree that most of you never have heard of), and dealing with loved ones that are or have been through blindness has taught me a bit about at the very least observing what does and does not work. Those that know me are aware of my own vision, while remarkably good in my youth my eyes do work independently of each other.
What I have observed in this thread is that you all are trying to prove scientifically that one phenonmenon is occurring. Medically speaking I should have no depth of field, and therefore should be prohibited from driving and other activities. The human machine can adapt and overcome, not all things that are true for a majority of people are necessarily true of every person, this is especially true with light and vision and what the mind "sees".

Writing down all the possible conditions for every person is a mind boggling task. My thoughts are try it, see what you observe and most of all remain open to thoughts and suggestions especially from local people to a range that you might be shooting on.

I must go prepare myself and my work equipment for another 'unstablizing' hurricane.
Mary

[BlauBear]

Good points, Mary.

Several have commented on temperature and ammunition, and I keep ammunition in a cooler at the range so the temperature is stable, but my observation is that hot ammunition (Eley Club in this specific case) is erratic, not consistently one way or another, and that it degrades with regular exposure to heat. I didn't bring it up because debating one variable at a time is plenty.

[Innocent]

BB,
Temp is usually related to the angle and amount of sun light...oh boy more variables.
I have no doubt that ammo will respond to temp variables in different ways. Again there are multiple variables being introduced here including the chemical stability of the powder, especially with regard to humidity.

Science is so exact. LOL

Mary

[Bob259]

I'm getting a headache

There is also the angle of the dangle theory that we haven't even touched yet

[stsbuyer]

BB,
Temp is usually related to the angle and amount of sun light...oh boy more variables.
I have no doubt that ammo will respond to temp variables in different ways. Again there are multiple variables being introduced here including the chemical stability of the powder, especially with regard to humidity.

Science is so exact. LOL

Mary

I thought all we had to do was dial in the setting put the dot on the animal and pull the trigger. How the heck have I ever been able to hit a target with light and tempeture causing so much trouble.

LOL Paul