What causes POI to wander?

[drop_point]

Recently, Keith from "Winning in the Wind" discovered the preferred load which also shot the smallest groups actually had the largest combined group. Further investigation revealed the center of that group tended to "wander" from point of aim. Likely, such a load may result in worse scores than loads that shoot a bit larger but have more consistent point of impact.

What causes a load to "wander" while a very similar load tends to shoot more consistently?

 

[markm87]

Good question. We have a Geissele Super Duty AR that's a really accurate gun. But after a number of rounds the POI will walk down about 4 MOA and right about 2 MOA. It did this in a 5 round group while I was shooting.

We watched a sub MOA AR go to like 5 MOA in one group. We re-zero'd the nightforce, and then my buddy cleaned the barrel, and the POI went back to the original spot. Absolutley nuts.

 

[Coyotefurharvester]

I assembled an AR upper with a hand guard I had never used before. Manufacturer stated 75 ft lbs torque on the barrel nut. I would shoot several groups(load development) and than a day or 2 later shoot to confirm. What had been 1/2" or better at 100 yds was high right and 1". I blamed my loads(20p) as it was a new cartridge for me. After several go rounds(optics change) etc. I pulled the hand guard, I could see the barrel nut was tight to the receiver face. I had a machinist friend take 0.030 off the nut. Now it would torque with clearance. Put back to together, similar results, now I'm blaming the barrel. Decided to check my torque wrench, 37 lbs actual torque at 75# setting. Calibrated the torque wrench, reassemble now that rifle shoots consistently and very accurate. Had a digital scope mount cross bolt that the previous owner must have stretched the threads on. That would lead to a high left poi shift over about 2 weeks of cold/warm cycles winter hunting as the nut would loosen slightly. New base mount and never another poi shift.

 

[6BRA]

Videos | wheeleraccuracy

www.wheeleraccuracy.com

watch straight stocks track.
Then ask yourself, why did he shoot 10 shots so fast?

 

[M-61]

Calibrated the torque wrench,

Caught my attention.
What make torque wrench and model?
How was it ‘calibrated’? By whom?
Really want to know as I have quite a few.
I don’t wonder about the beam type (Stutevant) as I doubt anything happens to them. But that’s foot pounds (lbsft) .
My inch pound ones are not. Is there even an inch pound beam style?

 

[gunsandgunsmithing]

I watched his video and maybe he'll clarify but, we've known for decades that tune changes as conditions change. I didn't notice in his video how much time he spent with his testing with any specific load but it had to take some time. I don't remember the details but a 33 shot group and multiple others at different setting took some time. I'd need more info but for now, I think condition changes that affect tune may be what's at play.

 

[jwink]

When my POI wanders, it's usually accompanied by my brain.

 

[drop_point]

I watched his video and maybe he'll clarify but, we've known for decades that tune changes as conditions change. I didn't notice in his video how much time he spent with his testing with any specific load but it had to take some time. I don't remember the details but a 33 shot group and multiple others at different setting took some time. I'd need more info but for now, I think condition changes that affect tune may be what's at play.

I believe he shot them round robin, and the load with the smallest groups had the wandering POI, while the other loads were more consistent. I'd like to hear his thoughts here.

 

[Straightshooter1]

Recently, Keith from "Winning in the Wind" discovered the preferred load which also shot the smallest groups actually had the largest combined group. Further investigation revealed the center of that group tended to "wander" from point of aim. Likely, such a load may result in worse scores than loads that shoot a bit larger but have more consistent point of impact.

What causes a load to "wander" while a very similar load tends to shoot more consistently?

From what I've observed in my shooting and chronoing every shot, changes in velocity is a cause for the load to "wander". Velocity changes could be a result of rate of fire in connection with changes in ambient temperatures. As I focus on Mean Radius of my groups, I can see this "wandering" as it correlates with changes in velocity. Velocity's relationship with barrel harmonics is a big part of that.

 

[6BRA]

Heat and bases moving from expansion? Bbl heat? Scope light refraction...perhaps your not really shooting where the reticle is showing? Picking a condition may be more involved than just wind.

 

[JFrank]

I watched his video and maybe he'll clarify but, we've known for decades that tune changes as conditions change. I didn't notice in his video how much time he spent with his testing with any specific load but it had to take some time. I don't remember the details but a 33 shot group and multiple others at different setting took some time. I'd need more info but for now, I think condition changes that affect tune may be what's at play.

Mike, I haven’t watched any video’s but I have to agree with you that tune changes and when poi shifts that to me is an indication of an unstable load that needs review.

Jim

 

[gunsandgunsmithing]

From what I've observed in my shooting and chronoing every shot, changes in velocity is a cause for the load to "wander". Velocity changes could be a result of rate of fire in connection with changes in ambient temperatures. As I focus on Mean Radius of my groups, I can see this "wandering" as it correlates with changes in velocity. Velocity's relationship with barrel harmonics is a big part of that.

Lots of possibilities. I only go by what I see on the target, literally thousands of times and over and over again. IME, if I'm completely out of tune, the mean radius will be larger than my completely in tune mean radius, virtually, if not 100% of the time. Now, there are places in between, if I don't keep up with tune as conditions change, that may well defy that and agree with what he saw in his test. In a nutshell, just my experience now, but in tune shoots better than completely out of tune, by whatever means.

Maybe I'm misinterpreting something, as I often do. I'm not changing though. There's a method to my tuning process that tells me what I'm looking for and why. I've conveyed it on here several times and if you choose a different path that's fine too. There are different standards of accuracy for different games too. For me, a gun that won't shoot pretty consistent mid teens at 100 yards in good conditions, there's something wrong somewhere. But knowing that and having that level of accuracy allows me to trust what I'm seeing much more than if the gun was only capable of shooting say....300's on those good days. Is that the gun, the shooter, the conditions, the tune or what? I can't answer that for every gun and every shooter but it's my standard, regardless of competition discipline. Not talking hunting or even varmint rifles here, but what I know it takes to win at the highest level. I'll take a gun that will consistently shoot mid .1's with no big groups over a gun that shoots zero's when the stars all align just right. If you have a mid teen rifle, you'll statistically get a few zero's and a few .250's. But I wouldn't call either a surprise. Rather, it's what I'd expect. Who knows what it'd do in perfect conditions because I simply don't know anyone that shoots in a vacuum.

 

[Straightshooter1]

Lots of possibilities. I only go by what I see on the target, literally thousands of times and over and over again. IME, if I'm completely out of tune, the mean radius will be larger than my completely in tune mean radius, virtually, if not 100% of the time. Now, there are places in between, if I don't keep up with tune as conditions change, that may well defy that and agree with what he saw in his test. In a nutshell, just my experience now, but in tune shoots better than completely out of tune, by whatever means.

Maybe I'm misinterpreting something, as I often do. I'm not changing though. There's a method to my tuning process that tells me what I'm looking for and why. I've conveyed it on here several times and if you choose a different path that's fine too. There are different standards of accuracy for different games too. For me, a gun that won't shoot pretty consistent mid teens at 100 yards in good conditions, there's something wrong somewhere. But knowing that and having that level of accuracy allows me to trust what I'm seeing much more than if the gun was only capable of shooting say....300's on those good days. Is that the gun, the shooter, the conditions, the tune or what? I can't answer that for every gun and every shooter but it's my standard, regardless of competition discipline. Not talking hunting or even varmint rifles here, but what I know it takes to win at the highest level. I'll take a gun that will consistently shoot mid .1's with no big groups over a gun that shoots zero's when the stars all align just right. If you have a mid teen rifle, you'll statistically get a few zero's and a few .250's. But I wouldn't call either a surprise. Rather, it's what I'd expect. Who knows what it'd do in perfect conditions because I simply don't know anyone that shoots in a vacuum.

I get what you're saying. But I was trying to address the OP's question about the "wandering" of the center of the groups rather than the changing size of the groups.

 

[gunsandgunsmithing]

I get what you're saying. But I was trying to address the OP's question about the "wandering" of the center of the groups rather than the changing size of the groups.

The bbl moves and that changes poi...err center of groups. I can't put it more simple than that my friend. It moves least when perfectly tuned though.

 

[ShtrRdy]

Recently, Keith from "Winning in the Wind" discovered the preferred load which also shot the smallest groups actually had the largest combined group. Further investigation revealed the center of that group tended to "wander" from point of aim. Likely, such a load may result in worse scores than loads that shoot a bit larger but have more consistent point of impact.

What causes a load to "wander" while a very similar load tends to shoot more consistently?

If I understood his test, he used three different seating depths.

 

[RabbitSlayer]

Im going to default to Hornady, your groups are too small. I now shoot 20+ round groups at one aiming point to confirm all loads. Without any math etc, my groups no longer wander. All of them are within the cone of dispersion. If your problems are more than a minute though, you got bigger problems...Even my cheap ruger AR holds 20 in a minute with handloads and moderate priced factory ammo in 1.5 minutes ish...

 

[drop_point]

If I understood his test, he used three different seating depths.

Yes

 

[drop_point]

Im going to default to Hornady, your groups are too small. I now shoot 20+ round groups at one aiming point to confirm all loads. Without any math etc, my groups no longer wander. All of them are within the cone of dispersion. If your problems are more than a minute though, you got bigger problems...Even my cheap ruger AR holds 20 in a minute with handloads and moderate priced factory ammo in 1.5 minutes ish...

The groups were 33rds

 

[K22]

While I am not a competitor, I do spend a lot of time on the range. Here is a list, based on my experience, of POI changes I have experienced and the causes as best as I could determine them:

1. A faulty scope - confirmed by testing.

2. Aggressive copper removal - first shot flyers and need to re-condition bore before POI returned to desire location - confirmed by testing.

3. Inadequate bedding - pressure points at end of stock - classical cheap Remington bedding system - confirmed by testing after pillar bedding and free-floating barrel.

4. Temperature Changed - changes in elevation from summer to winter shooting seasons - confirmed by testing.

5. Wind and Mirage - this is more speculative and difficult to confirm but I have noticed shifts at 200 yards at the range. Intuitively, this is very plausible if you examine wind drift charts. Mirage is more difficult for me to predict but its effect is real.

Personally, I have not noticed any tuned and tested loads causing POI shifts or at least that I could confirm by testing.

 

[762willdo]

temperature………..