Range Report POI Shift

D

dmgreene

Sergeant
Full Member
Minuteman
Sep 30, 2007
281
0
Old Salem, AL
#1
I have got a problem that I can't seem to fix. I have a rifle that the point of impact will change either up or down but sometimes it will hold the same POI for several range trips. The action has been in 2 different stocks that have been bedded correctly and the action screws are torqued the same every time. All the base and rings screws have been checked and double checked and I have never found any thing loose. The barrel is free floated and is nowhere close to touching. The POI shift is always vertical. This rifle will shoot 1/2 moa and better day in and day out but I never know where to start out. It will hold perfectly maybe 3 range trips in a row and then the next time out it may be anywhere from 1/2 to 1 1/2 moa high or low. This sucker cost me money at the last shoot I went to and I am beginning to think it is the scope. Anybody had any similar problems?

David
 
#4
Re: POI Shift

Quit cleaning the rifle's barrel.
smile.gif


Just do the action, bolt, chamber and outside dust.

John
 
#5
Re: POI Shift

Sniper1 the scope is a NXS. I didn't put it in there because you always get into "it can't be scope because it's a Nightforce" or "you need to buy a S&B and get rid of the Nightforce".

Grump the scope is the last variable that I can think of unless someone else point out something else. The only reason I haven't changed the scope is because it doesn't show any more problems once you reset the zero. I have actually quit resetting zero. I have started checking zero at 100 yards and adding or subtracting clicks according to what the 100 yard target indicates because the zero will eventually return to the original setting after few range trips. I can run targets from 100 to 500 yards and back again several times with no problems.

John I have shot a clean barrel against a dirty one and it makes very little difference if any at all. I usually clean every 50 rounds and I don't clean very aggressively. The Krieger barrel cleans up quick and easily.

Thanks
David
 
#6
Re: POI Shift

When you check your zero,are you shooting in the same position everytime?If you check it on a bipod,are you loading the bipod exactly the same everytime?For me,that makes a big difference,I make sure I put the same amount of preload on the bipod,or my POI will change.
 
#7
Re: POI Shift

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: dmg264</div><div class="ubbcode-body">I have got a problem that I can't seem to fix. I have a rifle that the point of impact will change either up or down but sometimes it will hold the same POI for several range trips. The action has been in 2 different stocks that have been bedded correctly and the action screws are torqued the same every time. All the base and rings screws have been checked and double checked and I have never found any thing loose. The barrel is free floated and is nowhere close to touching. The POI shift is always vertical. This rifle will shoot 1/2 moa and better day in and day out but I never know where to start out. It will hold perfectly maybe 3 range trips in a row and then the next time out it may be anywhere from 1/2 to 1 1/2 moa high or low. This sucker cost me money at the last shoot I went to and I am beginning to think it is the scope. Anybody had any similar problems?

David</div></div>

Making some assumptions, like insensitive powder and equipment that's not broken, the only thing that's inconsistent is you. Remember, since recoil is an angular concept, a consistent position, where recoil is manipulated to become predictable, is necessary for bullets to go where aimed. Be sure to check elbows, non-firing hand, stockweld, butt to shoulder, and grip for consistent placement.
 
#8
Re: POI Shift

Cheekweld, for starters. Find the right one, mark it on the stock with a bandaid pad so you can recognize its feel against your cheekbone, then try it abuncha times. May be the shortcut to a solution. Shortcuts do not always exist, but are sometimes worth a try.
 
#9
Re: POI Shift

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: KQguy</div><div class="ubbcode-body">When you check your zero,are you shooting in the same position everytime?If you check it on a bipod,are you loading the bipod exactly the same everytime?For me,that makes a big difference,I make sure I put the same amount of preload on the bipod,or my POI will change. </div></div>
Yes, check this above. And it could also be your breathing. Also, the weather does have some effect on POI. Large temp swings from cold to hot can change up POI. I have been puilling my hair out as well for some POI shifts on my 260. But it's mainly me causing these problems.
 
#10
Re: POI Shift

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ChadTRG42</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: KQguy</div><div class="ubbcode-body">When you check your zero,are you shooting in the same position everytime?If you check it on a bipod,are you loading the bipod exactly the same everytime?For me,that makes a big difference,I make sure I put the same amount of preload on the bipod,or my POI will change. </div></div>
Yes, check this above. And it could also be your breathing. Also, the weather does have some effect on POI. Large temp swings from cold to hot can change up POI. I have been puilling my hair out as well for some POI shifts on my 260. But it's mainly me causing these problems. </div></div>

"Could be your breathing", I doubt it as most folks will shoot during a natural resp. pause. As far as temp. goes, expect a 50 fps change in velocity with a 20 degree change in temp when using sensitive powder. That's worth about 1 MOA in sight correction. Still, the shooter's problem here is likely not understanding the importance of honoring the elements and factors of a steady position.
 
#11
Re: POI Shift

If you are adding or subtracting clicks to get to zero and then shooting fine there is a problem with the optic or in the base/ring mounts. That a$$uME's that you are correct in your assessment of the stock/bedding/etc.

If you add/subtract and then have to chase your zero later I'd be leaning towards position and cheek weld.

Other things to isolate.

Parallax backlash (did you dial from infinity to the correct setting w/o going back on the knob? )

Power setting: Some SFP scopes will exhibit a wandering zero as you go through the power range.

Bipod tension / adjustment to the rifle itself.

Cheers,

Doc
 
#12
Re: POI Shift

First guys I want to thank y'all for all the input. I going to try to give some more input.
First off I'm shooting off of an adjustable front rest with a bag under the rear of the stock, no bipod.

Sterling Shooter I pay very close attention to shooting form and breathing. Not saying that I do everything perfect every time but it usually shows up in group size more so than POI when I'm having a bad day. Also I am usually shooting more than one rifle and this is only one that the POI changes this much.

Greg as far as cheek weld goes, this particular rifle has an adjustable A5 stock and is the best fitting stock that I have. When I lay my cheek on this stock the full sight picture is there with only very minor adjustment if any have to be made.

Chad as far as temp swings right now we have 2 temps- Hot and Hotter than Hell. I have been shooting over the chrono and the velocity has been very consistent.

Doc I rezeroed this thing last range trip and I went today to check it again. Last trip it was 1 1/2 moa high, today it was 1 moa low. I very rarely touch the power ring. It stays maxed out at 15x. As far as the parallax goes I don't go infinity and then back because the sight picture and parallax come together no matter which way I adjust the knob. I had one Leupold that I had to adjust that way because if you didn't you were either parallax free or had a clear sight picture but never both.
 
#14
Re: POI Shift

How did you develope the load for this rifle,did you use the OCW method?Try shooting 3 .5 grains less than your load,3 with the same load,and 3 more with .5 grains more than you standard load.Then you can compare the POI,this might give you an idea if you are within the OCW.This may not have anything to do with your problem,but it may be worth looking at.
 
#18
Re: POI Shift

Doc I'm leaning toward the scope too. I think I'm going to get a little extreme the next time at the range. I going to take a rubber mallet and do a little "light tapping" and see what happens.

Sterling why do you think its the temp? Do you think that it may be affecting the rifle/scope or the load? I use the chrono quite regularly and it has been running within a 30 fps the last 5 months. Sterling you are correct about the records and that is something I have got to work a little harder on. I keep notes sometimes which isn't worth a lot. Usually I keep pretty good notes while working up a load and drop charts but after that I kinda get a little lazy.

Thanks again,
David
 
#19
Re: POI Shift

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: dmg264</div><div class="ubbcode-body">Doc I'm leaning toward the scope too. I think I'm going to get a little extreme the next time at the range. I going to take a rubber mallet and do a little "light tapping" and see what happens.

Sterling why do you think its the temp? Do you think that it may be affecting the rifle/scope or the load? I use the chrono quite regularly and it has been running within a 30 fps the last 5 months. Sterling you are correct about the records and that is something I have got to work a little harder on. I keep notes sometimes which isn't worth a lot. Usually I keep pretty good notes while working up a load and drop charts but after that I kinda get a little lazy.

Thanks again,
David </div></div>

I used to shoot my 6.5/284 in NRA LR. To win with it, at the HM level, pretty much, every shot had to be consistent in every way. For the most part, any inconsistency would bring about unpredictable recoil, assuring a bullet strike somewhere other than where desired. Since you allude to vertical POI shift, and, since you believe things like butt to shoulder and stockweld are indeed perfect, what else but temperature could trouble shooting lead to? BTW a 30 fps average change in muzzle velocity will be worth over a half MOA.

Of course, throat erosion is so rapid on a 6.5/284 that consistency of ammunition is quite elusive. One thing for sure, you don't have too much practice/load development opportunities with the 6.5/284 before the barrel has lost it's competitive edge, or freshness.

If you keep a score book up to date, recording things like wind and weather, even things like how you're dressed, you will certainly be able to correlate the conditions which result in any particular group,s divergence to what's expected, it's inevitable.
 
#20
Re: POI Shift

Have you had someone else shoot the rifle to see if they get the same results?

Also if you think it's the scope then put another scope on the rifle and see if that changes anything.
 
#21
Re: POI Shift

Sterling I'm not going to say that it can't be something I'm doing wrong but it's funny that I have several other rifles that I never have any problems with. As far as the 30 fps goes, I can see a difference at farther distances but I'm off the same moa no matter what the distance. If I'm off 1moa at 100 yards then I'm off 1moa at 500 yards. Make the 1moa adjustment and every thing is lovely no matter what the distance.

Throat erosion is pretty bad with a 6.5-284. I am adjusting for throat wear every 50 rounds. So far I am getting about .007" to .008" wear per 100 rounds. I have about 550 rounds through this rifle so far. In your experience is this about par for course? My first 6.5-284 I got about 1300 rounds through it before it really started going south but it was set up to shoot the 123 Lapua's. This one is running 140 Berger's and I don't know if I'm going to make 1000 rounds.

Well thanks again for all the thoughts. I'm heading to the coast for the holiday weekend. I hope everyone has a happy 4th of July.
 
#23
Re: POI Shift

I'm with the scope problem theory.

Unless the shooter's technique goes all to h e double-toothpicks when he's using a well-fitting stock, shooter error is unlikely based on no other rifles displaying the behavior.

Otherwise undetected bedding problem(s) might be at play, but changing scopes rather than doing the mallet-dance is really the only way to eliminate the possible scope problem. I'm wondering how far up the chamber area of the barrel the bedding goes...might be worth a look anyway.

I would expect that internal stresses in the barrel would still leave it hitting the same place when totally cold. Some barrels do funny things as they heat up.

If it were my rifle, I'd try the mallet thing first just to get the results before pulling the scope and bothering to re-zero with a different one. Maybe do both the same range session.
 
#24
Re: POI Shift

Throat erosion and the bullet seating depth will effect pressure/velocity making constent attention and chronographing a necessity. I think that's what's going on here. With my 6.5/284, erosion would bring about very high velocities. For 3000 fps, an initial load of 50.3 grains of RE-22 under a 140 grain SMK was required; however, after some erosion, it only took 47.5 grains for the same velocity under same conditions.
 
#25
Re: POI Shift

I went through the same thing with my 260s an 308s esp. in the summer when I shot the most. I never did find anything wrong with scopes guns or me. I had my son shoot the rifle an he had the same results as I did. I figured it was weather related.

Then I few years ago I got into drag racing again. Now it seems all the guys have weather stations to tell them what the DA (Densisity Altitude) is for the day or time their running the car.

What I soon discovered is that you can start off the day with a 800ft DA and end it with a 6000ft DA which means the car thinks its running in 6000ft air an will run like shit.

So I got to thinking that if my motor thinks its running at 6000ft then maybe the bullet thinks its flying in thinner air too. SOoooo... Maybe thats why the difference in points of impact from one day to the next.

I also was out shooting one evening when a front moved in an it was getting ready to rain an I was shooting at 800yd an had my impact change from one string to the next. So I belive its weather related.
 
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