2 MOA impact change at 700 yards?

[Zane in Oregon]

I have a 6.5/280 Ackley Imp that I have been shooting at 700 yards. I shot at the same target two days in a row with different results. One day I dialed 13.5 Min of elevation, and the next I had to dial 15.5 to hit center. The conditions were very simular on both days. The temp perhaps fell from 70 to 50, and the humidity could have risen from 70 to 90%. I have tried the JBM program to try to explain the difference in impact but have had no luck. There was almost no mirage as it was mostly cloudy on both days. I am stumped at this point. I am hoping someone can shed some light on the reason this can happen, other than a bad scope or mounts. It has a Leupold VX III 6.5-20x40 with 30mm tube, in Leupold mounts, which are tight. It's a Model 700 that shoots in the .5's. I'm just getting going at over 600 and have not had this problem so far, and I've shot a lot at 600.

Does my scope have a tracking problem?
Is there a mirage that I didn't notice that is making the target look higher on one day and not the other?
What else can make this happen?

Thanks for your time.

Zane

 

[Michael Eichele]

20 degrees can change your POI at 700 yards as can pressure. Did you document the barometer both days?? That can change rather fast and have a HUGE impact on your POI espesially coupled with a 20 degree swing. Although both together most likely wont account for 2 MOA but could account for 1 MOA. Different lighting conditions can play in on this as well. Also, since it was colder, your ammo could have been slower in the velocity department. All things concidered and 2 MOA at 700 yards isnt bad. Learn why and compensate for each and every variable. 600 yards is the threashold for "forgivness" from air density changes and such. 700 yards begins a whole new ball game.

 

[Zane in Oregon]

Thanks for the input.

I ran the JBM with these weather changes and could only come up with a 0.3 MOA change. I realize that the program could be off a bit. I did get the baro reading from a local weather station, but as I said it was only local, and not exactly where I was.

Thanks for the info, again. I'm still pondering.

Zane

 

[Brown Dog]

Zane,

With strange POI changes I used to find myself guilty of a tendency to 'hear hoofbeats and think of zebras' ...rather than consider the simple solutions;

With what you've described, rather than equipment faults or ballistic weirdness, my first thought (having (far too slowly) trained my brain to 'hear hoofbeats and think of horses')relates to your consistency of 'position and hold' from occasion to occasion. For example:

-different surface under your bipod?
-leaning into the bipod for 1 group; but not the next?
-pulling the rifle into your shoulder for 1 group but not the next?
-differing cheek pressure on the stock etc............

All the best

Matt

 

[Coyboy]

+1 Brown Dog

 

[lovdasnow]

hey zane, sorry to interupt this thread, but where do you live? I'm over in stayton, just wondering? good luck with your issues.