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  #1  
Old 05-16-2021, 11:29 AM
mstuhr
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Reasons for sudden POI shift



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I'd like to pick your minds and call on your experiences about POI shift.
I expect I know the answer but thought someone may have experienced something I'm unaware of or have overlooked.
I picked up a H&R M-12 and have set it up for 50 yd benchrest rimefire matches. I have a fine Walther UIT I picked up from Wahoo and have shot it last year and the start of this year and others in the past. I'm no expert but not exactly new to it.
The H&R shoots better than one reads about, but I can't bring myself to take it to a match as it has a sudden POI shift of about an inch and a half that pops up from time to time.
It groups good and seams to be a easy gun to shoot well. I was shooting it after getting it set up, good groups inside of small sighter on the bench rest rimfire target at 50. I switched to start shooting the card for score. I shoot bottom to top and shot well in the first row with two nines 3 x, switched to the second row and punched the sighter and started up the row. 10, 10 10 and the next shot went out and into the third row of targets. It was just practice so I shot the same target and cut the hole in the next row, one more and same out of the box POI.
I have a new Kounus 6x24 cross hair and illuminated dot shooting at 12 power (Club rules) and EGW mount, bubble level that I always use prior to a shot. I left the range with the gun zeroed
Next time out it is 1 to 1 1/2" out. All shooting was dead calm to calm wind.
When I got home I pulled the scope and mount off and bedded the mount to the barrel. While I had access to the action screws I pulled the action out of the wood and fiberglass bedded the rifle. It is a solid job with minor cosmetic flaws but trust me it isn't moving.
I retuned to the range this morning Sighted the gun in and shot a 237 withy Geco ammo. I was happy and took the rifle from the rest and placed it in a foam case on the next bench and started to pack. It was a pretty day and I thought I'd get to know the rifle a little better and took it from the case and placed it back on the rest and tried another card.
First shot was 1 1/2" low left. Fired four more thinking it might shift as it warms up and had a great group piled on the first shot. I made two adjustments to get it back to the center of the small sighter and shot a 244 (Hard to believe, but with Geco.)
I doubt it is the mount
I doubt it is bedding.
Everything scope related and action is torqued and loc tited
Trigger is smooth and just under a pound. I flushed it with acetone and oiled it while I had it out for bedding.
I really like this rifle.
I'm expecting something sticking in the scope adjustment. I'll shoot a box drill next time out. I ran the adjustments from stop to stop both windage and elevation several times . I don't know if it will help.
Anyway, I'd love to hear any ideas anyone might have.
My money says scope but if there is anything you might suggest to check before I send the scope back I would appreciate suggestions.
Many thanks
Mike
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Old 05-16-2021, 11:47 AM
flangster

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I have often experienced problems like these. A couple of things come to mind.

1. Ammo variability. A chronograph can help here, but it is hard to know what is happening without data on bullet speed.
2. Changes in rifle position or hold. Sounds like you know what you are doing, so I am not trying to be insulting. I often find that holding the rifle differently between groups will alter the POI. Little things like hand position, how hard you are pulling back into your shoulder pocket, exact position on the front or rear bags. . . replicating this from shot to shot is part of what makes rimfire such a challenge. I sometimes despair that I am not organized enough to take notes for each rifle/ammo combination.
3. Parallax. I know this sounds nuts, but I am never 100% sure that my eye position isn't messing things up for my own groups. You are supposed to know that your rifle is adjusted for parallax when you move your eye position a bit, but the cross-hairs remain on target. I have never had this level of adjustment in any scope I own. I suspect that it is easier/more precise with better scopes than the ones I use, which tend to be in the $300-600 range. But if moving your eye position moves where you perceive the cross-hairs to be, and you are not in exactly the same position from range trip to range trip, whether it is because you are not at the same bench or for another reason, this could easily move your POI by a quarter inch or more.
4. Finger position on the trigger. Sounds like you have a nice trigger set up. Many BR guys are setting their trigger in the low single ounces, not just under a pound. Touch the trigger the same way every time.

Just to be clear, the above are my own present concerns about my own shooting. If I could put five shots in a .250 inch group whenever and wherever I wanted I'd declare myself happy and move on to stamp collecting, or some-such. I'll be interested to read what others come up with here. Always looking for tips myself.
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Old 05-16-2021, 01:39 PM
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Quote:
Originally Posted by mstuhr View Post
I'd like to pick your minds and call on your experiences about POI shift.
I expect I know the answer but thought someone may have experienced something I'm unaware of or have overlooked.
I picked up a H&R M-12 and have set it up for 50 yd benchrest rimefire matches. I have a fine Walther UIT I picked up from Wahoo and have shot it last year and the start of this year and others in the past. I'm no expert but not exactly new to it.
The H&R shoots better than one reads about, but I can't bring myself to take it to a match as it has a sudden POI shift of about an inch and a half that pops up from time to time.
It groups good and seams to be a easy gun to shoot well. I was shooting it after getting it set up, good groups inside of small sighter on the bench rest rimfire target at 50. I switched to start shooting the card for score. I shoot bottom to top and shot well in the first row with two nines 3 x, switched to the second row and punched the sighter and started up the row. 10, 10 10 and the next shot went out and into the third row of targets. It was just practice so I shot the same target and cut the hole in the next row, one more and same out of the box POI.
I have a new Kounus 6x24 cross hair and illuminated dot shooting at 12 power (Club rules) and EGW mount, bubble level that I always use prior to a shot. I left the range with the gun zeroed
Next time out it is 1 to 1 1/2" out. All shooting was dead calm to calm wind.
When I got home I pulled the scope and mount off and bedded the mount to the barrel. While I had access to the action screws I pulled the action out of the wood and fiberglass bedded the rifle. It is a solid job with minor cosmetic flaws but trust me it isn't moving.
I retuned to the range this morning Sighted the gun in and shot a 237 withy Geco ammo. I was happy and took the rifle from the rest and placed it in a foam case on the next bench and started to pack. It was a pretty day and I thought I'd get to know the rifle a little better and took it from the case and placed it back on the rest and tried another card.
First shot was 1 1/2" low left. Fired four more thinking it might shift as it warms up and had a great group piled on the first shot. I made two adjustments to get it back to the center of the small sighter and shot a 244 (Hard to believe, but with Geco.)
I doubt it is the mount
I doubt it is bedding.
Everything scope related and action is torqued and loc tited
Trigger is smooth and just under a pound. I flushed it with acetone and oiled it while I had it out for bedding.
I really like this rifle.
I'm expecting something sticking in the scope adjustment. I'll shoot a box drill next time out. I ran the adjustments from stop to stop both windage and elevation several times . I don't know if it will help.
Anyway, I'd love to hear any ideas anyone might have.
My money says scope but if there is anything you might suggest to check before I send the scope back I would appreciate suggestions.
Many thanks
Mike
I would bet on the scope being bad, do you have another known good scope to try?

Lee
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  #4  
Old 05-16-2021, 01:51 PM
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I think flangster and Hi-NV Shooter have given just about all the reasons I can think of. My bet would be the scope followed by inconsistent ammo, then parallax error.
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Old 05-16-2021, 04:17 PM
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Try lightly tapping the scope turret between shots to see if it shifts. If it does you have a bad scope. It is a single shot but the only other remote possibility I can think of is improper loading.
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Old 05-16-2021, 04:47 PM
mstuhr
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Hi and thanks to all

Thanks,
I'd say I have to rule out ammo as the group size doesn't grow and when ever it moves it seems to stay there until you move it back to point of aim.
Parralax is good, trigger control is good and I try to set every shot up the same.
I'm going to try it once more after spinning the adjustments in and out and if that doesn't work I'll get a hold of Konus. Heck of it is, if they were to put it on a rifle and try it, it would probably seem just fine for a while.
The first time the shift came around the forty round mark. This morning it came between the first and second box of ammo. Remote possibility it was difference between boxes from the same brick but I kinda doubt it. I took it from the rest placed it in a foam lined hard case then removed it and sat it back on the rest and it had lost zero. It doesn't wander. It shoots where you point it up to the time it moves and then stays there until you move it back to point of aim. I am reasonably certain it's a scope thing
I appreciate everyone's input
Many thanks!
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Old 05-16-2021, 07:08 PM
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Try a different scope, I think you will resolve the issue.

I use to have a couple of Konus scopes, they did exactly what your describing. The first one was great for about 6 months ( the reason for buying the second one.) That one I returned three times, then finally exchanged it for a Weaver. Then the first one did the same thing. Traded it in on a another T36X.
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Old 05-17-2021, 07:28 AM
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not unusual for any rifle not properly bedded and sealed to pick up and lose moisture, more so from spring to summer. marty
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  #9  
Old 05-17-2021, 07:38 AM
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But not 1.5" @ 50yd after being put in a case for a while and taken back out.
I've had a couple that the internal lube had become sticky (I guess) so I ran the adj's back and forth a good ways 3x on the one and it settled down. The other Im unsure about...... I suggest letting them sit in the sun to heat up some, that old lube likely needs all the softening it can get.
Btw, both scopes were decades old and had sat unused for a long while.

Last edited by gcrank1; 05-17-2021 at 07:43 AM.
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Old 05-17-2021, 07:40 AM
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Spring in scope is slipping. You zero, it holds for a while, then reseats itself, you rezero , it holds for a while , then slips or releases , or twists, what ever , and poa changes . Send it in.
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Old 05-17-2021, 08:28 AM
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Great advice from fellow members! Trying a "known good scope" is high on the list. If the problem persist, you might take a quick look with the borescope to see if any "meanies" have gathered in the barrel. You might try some top dollar ammo your rifle really likes and see if the scores get better. Good luck and have fun!
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Old 05-17-2021, 09:56 AM
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Give the scope a couple taps with a rubber hammer to see if POI moves. If it does get out the 3# hammer.
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Old 05-17-2021, 12:16 PM
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My Nightforce 12/42, did that a few years ago. Sent it to the service center and a few weeks later, I got it back. Note said, "Scope was within spec's". Installed it on my BR Riffle, and haven't had a problem since. Seems they fixed it, but didn't want to admit it.
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  #14  
Old 05-20-2021, 05:46 PM
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I had a high end Bushnell scope go bad years ago, loose reticle, and I contacted Bushnell and I sent it in. They confirmed it had gone bad and they didn't sell or service this scope anymore. They sent me a replacement of the next higher level scope, much more expensive and better quality. Very nice of them!

I have had no further trouble with that scope.
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  #15  
Old 05-20-2021, 07:14 PM
mstuhr
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Bushnell

Hi Whig,
I have nothing to say bad about Bushnell service.
I had a similar experience with them.
I wish they made a affordable target dot scope.
Thanks
Mike
Update: I solved my problems today and ordered a Mueller 8x32 target dot scope like I have on the Walther.
I had the H&R out today and shot a 239 in horrific conditions with the Konus, then backed it up with a 200 when it calmed some and I shot more carefully. I could have held off but I wanted to shoot it just like I did the 239 only holding off for the wind
It suffered from a 1 1/2" shift to one o'clock early in the second card. A 200! That's funny!
Had you cut and stacked the targets there would have been a near 20 shot group out of 25 shots up and out at 1:00.
I'm going to send it back once the Mueller gets here. If they replace it I'll have one for sale. If they return it, it goes in the trash.
I really like the rifle. I still like Konus scopes, just not this one.
Many thanks to all who offered help and advice!
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