Zero shift?

[Boyd L.]

I've been reading Steve B's article in Precision Shooting (excellent work sir). The evaluation of ammunition and differing zeros at different distances caused me to wonder about other zero issues. I began to wonder if there is any evidence of how (or if) a zero will shift during a day of shooting with temperature change as the primary influencial factor.
For example, if one zeros a rifle at 8:00 a.m., will there be a predictable shift in zero by noon? Let's assume that the temperature raised from 65 degrees to 85 degrees during this timeframe.
I realize that so many factors prevent consistent barometric, temperature, and wind conditions from day to day that predictability may be difficult. Just wondering if anyone made a habit of automatically adjusting their zero or point of aim as the day heats up (or vice-versa), and what experienced is this based on?

Thanks,

Boyd

[Innocent]

Boyd, that is why some of us depend very heavily on our spotters. Yes, I do vary scope setting (not necessarily my zero, as that is my reference point to go back to) based tempertaure, lighting and humidity changes, all very easy to see and feel. Less easy for most people (except some of us with our ole buddy Arthur-itis) have a tougher time sensing barometric changes in the course of a day. I don't move a set amount based on temperature, I depend on my spotter, ir if a spotter is not available, I pick an edge shot and watch for the animal spin in my follow through.

Mary

[Trent]

I can't wait until I can "pick and edge shot"!!

[Innocent]

Trent, you can pick an edge shot, and hit it. Mental game.

Mary

[Bob259]

Trent, you can pick an edge shot, and hit it. Mental game.

Mary

Easy for you to say Mary...

[Boyd L.]

I can't wait until I can "pick and edge shot"!!

I was thinking the same thing. Six years of this stuff and I still can't.

Thanks Mary. The spotter can tell you how/where the shot went (if they could only tell me why). Just wondering about "trends" in POI as the day moves along.

[Innocent]

Boyd, The person I know with the most experience of 'trends' that you refer to (that is still alive)is Jerry Tureau. As for edge shots, they can be done, work on the mental game...pick a spot, shoot for it.

Now, many times a spotter can help with why a shot didn't work, but then you fall into the problem of not always being able to tell you where the shot hit. I have been spotted by my late mentor, him without a scope, or even watching down range and been told where I am hitting, tehcnique, follow through have so much impact on where the shot falls.
Mary

[Jerry G]

I have set up some experiments to check my ideas on the subject. I set up a transit on an x at 100 meters and every hour I would go look to see what changed on the immage. As the sun moved across the sky, the immage would shift in relation to the cross hairs. I was sure I was on to something. To check my findings, I zeroed my SB rifle at 100 meters and shot a group. I shot groups every hour for the entire day. Much to my surprise, I couldn't see any change in group location that amounted to anything. To take this one step farther, this year at the CBC, I did notice that my sight setting for the rams varied over the course of 2 days. It did show up in what Mary was describing with a good spotter. Last Sunday I had a shoot-off on pigs at the ram berm (exploding pig game shoot-off). I used my ram settings from earlier in the day and the first center break went over the back of the pig. The next shot was broken deep in the belly and knocked the pig over with a center and right hit.

Bottom line in my opinion is. Get your basic settings and work off of them. The rest is dependent on how sure of your break you are and your spotter's call. There are way too many factors that effect the shot, wind, temp, humidity, bar pressure, and light. I think many people try to think the problem to death and should depend on the tried and true basics.

[Jason]

That sure sounds like a whole lot of planning and organization for someone who forgot to come to the line and shoot when it was his relay, Jerry...

[Jetmugg]

We often have matches in January and February to avoid scheduling conflicts at the range. It is not unheard of for temps to be in the single digits (F) when sighting-in begins at 8:00 in the morning. When it's that cold, there are definitely noticeable changes throughout the day, particularly if a match doesn't end until 1:00 in the afternoon. By noontime, the temp might be up in the mid-toupper 20's (F). I'm not sure whether it's due to the ammo, or due to the rifle, but there can be multiple MOA differences between 8:00 a.m. and 1:00 p.m. on a cold day.

2 cents.

SteveM.

[Innocent]

Jason, see Jerry's remark about the HP shooters being a bit strange....hmmm guess age is catching up with him, I've known all alaong that he is confused about where he lives.

Innocent

[Innocent]

JetM, I have seen as much as six inches of movement over the course of a full day, depending on all the variables.
M

[Boyd L.]

..... I shot groups every hour for the entire day. Much to my surprise, I couldn't see any change in group location that amounted to anything. To take this one step farther, this year at the CBC, I did notice that my sight setting for the rams varied over the course of 2 days. It did show up in what Mary was describing with a good spotter. Last Sunday I had a shoot-off on pigs at the ram berm (exploding pig game shoot-off). I used my ram settings from earlier in the day and the first center break went over the back of the pig. The next shot was broken deep in the belly and knocked the pig over with a center and right hit....

...JetM, I have seen as much as six inches of movement over the course of a full day, depending on all the variables.
M...

Steve mentioned in his article that at the chicken line, the POI seems to move vertically as the day progressed. One would think (or at least me... ) that this would be more pronounced at each successive range. However the consensus here seems to be that there will be changes, just not certain what direction, when, or to what degree. Sounds familiar....

[Innocent]

Taking wind out of the variables, low light and or lower temperature, shots drop (usually), higher temp and brighter light shots tend to go higher. Now add the wind, angle of firing (up hill/down hill...etc.) that may change. BAR tends to alter the flight of bullet some, but not usually noticable until you get out to the farther distances. Very vague I know, but that is where having a spotter, especially one that knows the range and the local prevailing winds and you can trust/communicate with and you've got a tough pair to beat.
Mary

[Trent]

Trent, you can pick an edge shot, and hit it. Mental game.

Mary

I have a lot of work to do though. And mentally... I am at a disadvantage!