POI shift between range trips.

[Huntnful]

So this has been bugging me, and I'm curious if its common/normal or correctable. I've been consistently noticing left/right POI shifts randomly throughout range trips. NEVER up and down. Just left/right. Sometimes 1/2", sometimes 1", sometimes nothing at all. I never noticed this at all last year, but after 7 backcountry hunts, I'm noticing it, and wondering if I did something while hunting/packing meat. Been doing a lot of tinkering/load development now that it's the off season and making tons of trips to the range. Even shooting the same load as the prior trip, sometimes I will see a shift. The gun is a custom 28 nosler and a tack driver. Consistent 1/2 MOA with several loads. What could be causing this? Is it me? Is it normal? Is there something minute with the rifle that could cause this that I should look into?

I shoot from the same position every time I go to the range. So I'm not changing any aspects about the rifle support or anything also. I also tested out 3 scopes since the off season and have noticed it with each scope. VX-6HD, NF ATACR and NF NX8. So it's either something I'm doing, something my rifle is doing, or normal/common. But 100% not the optics.

 

[Gunpowder]

I'll be interested in what others have to say on this. I'm assuming you ruled out wind variation? How about scope mounts? Different lighting, different times of day with sun position, clouds or not, etc have caused some vertical changes in my poi. My range faces west, so right into the sun in the evenings in spring and fall. After sun set, my groups will be noticeably, measurably higher. On a previous range that faced south, groups tended to shift to the right after sunset. I couldn't figure it out, but another shooter suggested that might be the cause.

But I don't know, will be curious what others come up with on this one.

 

[Deleted member 115360]

Just speculation, but how many rounds have been pushed through that barrel? I have heard of barrels that continued to get poi shifts until nearing the 100rd mark. The public school terminology for dummies like me would be to call it: "barrel break in".

I really hope that isn't the case in your situation with that cartridge, because that would make for an awful short usable barrel life.

 

[Deleted member 115360]

One more question? Are you cleaning the barrel between range trips? If you are using a copper solvent each time between trips, it could potentially cause a poi shift.

 

[cdherman]

Does the gun have a wood stock? Fully pillar bedded? Temp and humidity can cause shifts, especially with wood stocks. And I'd pass a dollar bill down between the barrel and stock. Make sure nothing touching. I had a seed get down between the barrel and stock once that messed up the free float and accuracy.

Also, are you taking the action out of the stock to clean or inspect after shooting sessions? You might need to invest in a proper torque screwdriver to make sure you are re-torquing the action the same each time.

 

[cjuve]

Do you check to make sure that your scope is parallax free prior to shooting?

 

[Huntnful]

I'll be interested in what others have to say on this. I'm assuming you ruled out wind variation? How about scope mounts? Different lighting, different times of day with sun position, clouds or not, etc have caused some vertical changes in my poi. My range faces west, so right into the sun in the evenings in spring and fall. After sun set, my groups will be noticeably, measurably higher. On a previous range that faced south, groups tended to shift to the right after sunset. I couldn't figure it out, but another shooter suggested that might be the cause.

But I don't know, will be curious what others come up with on this one.

This is super interesting! I always shoot randomly through the day, whenever I can get out, down a certain dirt road and never even consider where the sun is. It could literally be this simple haha.

Gun is freefloated, plenty of room around the barrel, and bedded into a composite stock. But I haven't removed the action/barrel from the stock since I've bought it. I have checked to make sure it's still torqued down though, which it was. I also always adjust the parallax out.

 

[Huntnful]

I just removed the action from the stock and also found a possible culprit. A small piece of branch lodged right near the recoil lug

 

[Doom2]

I would almost bet its your setup and hold that is slightly different on the different days. Pay particular attention to trigger follow through.

 

[Huntnful]

I would almost bet its your setup and hold that is slightly different on the different days. Pay particular attention to trigger follow through.

It could easily be this. I try to be as consistent as possible, but I'll definitely focus on the trigger follow through now also!

 

[cdherman]

View attachment 256114
I just removed the action from the stock and also found a possible culprit. A small piece of branch lodged right near the recoil lug

Please do post back if the piece of debris turns out to be the culprit. Had it happen to me once, but in my case, the seed was further down the channel towards the end of the stock.....

 

[Radman]

So this has been bugging me, and I'm curious if its common/normal or correctable. I've been consistently noticing left/right POI shifts randomly throughout range trips. NEVER up and down. Just left/right. Sometimes 1/2", sometimes 1", sometimes nothing at all. I never noticed this at all last year, but after 7 backcountry hunts, I'm noticing it, and wondering if I did something while hunting/packing meat. Been doing a lot of tinkering/load development now that it's the off season and making tons of trips to the range. Even shooting the same load as the prior trip, sometimes I will see a shift. The gun is a custom 28 nosler and a tack driver. Consistent 1/2 MOA with several loads. What could be causing this? Is it me? Is it normal? Is there something minute with the rifle that could cause this that I should look into?

I shoot from the same position every time I go to the range. So I'm not changing any aspects about the rifle support or anything also. I also tested out 3 scopes since the off season and have noticed it with each scope. VX-6HD, NF ATACR and NF NX8. So it's either something I'm doing, something my rifle is doing, or normal/common. But 100% not the optics.

Laugh all you want but I always see an aggravating difference from spring to late-fall. I keep everything very consistent so I have always written it off to thermal expansion/contraction within my scopes. JMO

 

[new2mud]

After sun set, my groups will be noticeably, measurably higher.

Thermal compression is real—as the sun sets and the cooler (denser) air starts to settle toward the ground, the air creates a falsely compressed picture of the target. This results in shots landing off the vertical POA since the target itself hasn't actually compressed.

 

[new2mud]

I should add that the thermal compression I mentioned above shouldn't affect horizontal POI shifts, (unless shooting gangsta-style?).