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Changing POI

 
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  #1  
Old 05-20-2013, 01:25 PM
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Join Date: Mar 2008
Posts: 89
Changing POI

I’m trying to solve a changing POI and wondering if anybody has had this happen to them. I’ve tried this with two different guns and the results are the same. I put the gun in a barrel vise and wrap my hands around the scopes objective bell and the barrel or the barrel and stock and squeeze about as hard as a firm handshake and release. This applies downward pressure on the scope, if I look through the scope at the target the cross hairs moved about 1.25” at 100 yards. I can then use two fingers and wedge between the bell and barrel, this applies upward pressure on the objective bell then release and look through the scope again the cross hares will move back. I have verified this at the range. It shoots 2 nice .4” groups 1.25” apart all vertical. One gun is a defiance action with Seekins base and rings the other is a 700 with Nightforce rings and bass both have NXS scopes on them. I am very particular when mounting the base and scope and have checked and rechecked everything. I also put a dial indicator on the base to see if it moves relative to the action and it's rock solid. any thoughts on this

Sorry the photo came out rotated 90 deg. the two groups are actually top and bottom
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  #2  
Old 05-20-2013, 01:51 PM
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Join Date: Oct 2008
Location: Alabama
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Re: Changing POI

Had the POI change a couple times on a couple different guns. For mine it was crosshairs were broke, or something was loose in the scope mounting.

I have no idea what could be going on with yours. Do you have your forward scope ring far enough forward to properly support the big objective bell with a large magnum, so it isn't vibrating too much? B/c that can sometimes cause what you are describing.
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  #3  
Old 05-20-2013, 02:07 PM
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Join Date: Mar 2008
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Re: Changing POI

It's a heavy 14 # gun shooting a 260 Remington so it's not a magnum. I did play with the front ring placement moving it as far forward and backwards as I could and the change was always there. I only used the barrel vise to verify the movement when I did this. The ring was half way between the turret and the objective bell when I did the range test.

I think I have always had this problem with the Defiance but I installed a break and it made the problem really worse. Before the Break my groups would show signs of vertical stringing about .75" about 50% of the time and other times it would be nice .3-.4" groups. I always thought it was my technique.
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  #4  
Old 05-20-2013, 02:26 PM
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Join Date: May 2007
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Re: Changing POI

So you only get changing POI when you push or pull on the scope?
I don't follow your question?
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  #5  
Old 05-20-2013, 02:46 PM
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Join Date: Oct 2008
Location: Alabama
Posts: 6,339
Re: Changing POI

Make sure your action screws are torqued properly, and make sure your barrel is 100% free-floated and that nothing is touching.

Could also need to bed your action to the stock.

Sounds to me like barrel harmonics if the muzzle brake made it worse...
__________________
"I'm just a peckerwood who lives in the hills with too many guns..." - Bob Lee Swagger

"Give me a minute...I'm good. Give me an hour...I'm great. Give me 6 months...And I'm unbeatable." - Col. Hannibal Smith

Ignore everything I say, because I have a reading comprehension and memory problem...

Quote:
Originally Posted by WildRose View Post
The 284 is to the STW what a tricycle is to a Ninja.
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  #6  
Old 05-20-2013, 02:52 PM
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Join Date: Mar 2008
Posts: 89
Re: Changing POI

The POI change happens all the time but its hard to know when and how much when you are shooting in the real world, the recoil changes it, if I pick the gun up by the scope or put pressure on it when getting into a shooting position. The range test I did only changed one thing. I didn't move the gun off its rest all I would do is put upward pressure on the scope and shoot one shot then put downward pressure then shoot one shot, I alternately did this to get the two groups in the photo.
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  #7  
Old 05-20-2013, 03:03 PM
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Join Date: Mar 2008
Posts: 89
Re: Changing POI

The barrel is floated and the action is bedded. I've tried really hard to duplicate the problem without touching the scope and I cant, i've tried prizing and pulling everything without touching the scope and it doesn't have ay affect until i mess with the scope. I removed the break and ran the test and I get the same results.
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