7mm Mag Sendero Question

[luke5678]

I live in Oklahoma at about 500 ft. elevation. I have a factory 7mm Mag Remington Sendero that I have had for two years. I recently did a mule deer hunt in Wyoming at 8,000 ft. elevation. I double checked my 200 yard zero in OK before I left and put it in the pelican case. To my surprise, when I got to Wyoming I shot several times at range and it was grouping 4 inches low at 200 yards.

Does anyone know why the gun would shoot 4 inches lower in Wyoming than Oklahoma? I did not bump nightforce scope and shooting same batch of handloads. I shoot IMR 4350 which is not an "extreme" powder but I wouldn't expect different results and if any I would think it would shoot higher in Wyoming due to higher altitude.

My MOA data out to longer ranges also proved to be significantly different as well. Any thoughts on what would be going on?

 

[SBruce]

I'd be suprised too! But really, you're not alone. I am amazed by the number of people that have to re-adjust their sights when they get out here. I see it every year, at least a couple of times..........don't have a proven answer as to why, but it happens.

Seems like a 2 minute shift is quite excessive though.? Was your data and drops (in Wyoming) different enough to suggest a major change in load velocity? Or, did the drops come out right after a scope adjustment?

I've heard some prarie dog shooters say that they want to shoot all their ammo while they're here, because by next year, the vibrations of another round trip will have their ammo shooting differently (supposedly breaks down the powder grains).

 

[4bycamper]

Does anyone know why the gun would shoot 4 inches lower in Wyoming than Oklahoma?
My MOA data out to longer ranges also proved to be significantly different as well. Any thoughts on what would be going on?

I did not know that IMR 4350 was that temperature or air pressure sensitive, but that is my best guess.

 

[Sendero_Man]

temp difference between sight in at home and here ?

I now only shoot Hodgdon powders because of things like this. I have had RL25 and 17 shift as much as 350 fps in the temp. changes here in WY.

They shoot great groups, but when your POI is off 3.5 to 4 inches at 200 yards ... critters get wounded or missed.


another question.... how did it shoot now that you are back home ? difference again ?

 

[MHO]

4 inches low has me puzzled. I tried the "extreme" powders and through what little tests I tried I RAN back to my old IMR. Something beyond me to explain that. Look forward to hopefully someone explaining it. I do the opposite. When we leave Colorado to Kansas, Nebraska and Oklahoma. About 5 tp 6 k in elevation change we have to adjust a little. Not 4 inches at 200 yards.

 

[fmajor]

I'd be thinking the change in temps would be #1 on my list also.

Aside from this - did you re-check you zero once you got home? Be interesting if it 'returned' to where it was...