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Bore Sighting & observations

 
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  #1  
Old 11-12-2004, 11:33 AM
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Bore Sighting & observations

Am I bored or that???

For a long while I've been bore sighting my rifles during scope installation and I'm pretty good at it. Things like the crosshairs must be below the reticle to allow for the drop of the bullet, basic stuff.

What I've recently seen is that not all rifles bore sight the same.

During a recent shoot in NC I pulled out my backup rifle to check it zeroed before a match. I noticed it was about 2 to 3 MOA off center (windage) barrel pointing to the right. The barrel is free floated and not bound in any way and the rifle shoots fine and accurate AND was zeroed as shown by subsequent live fire tests.

I'm having just a little difficulty understanding why this rifles bore must be pointed so much to the right for it to be zeroed. I've seen a few others that were a little right or left but not so much as this one.

As a note: I've begun carring a Leupold Bore sight to verify my rifle zero. I have the rifle zeroed at 100 yards and THEN use the Leupold Bore Sight to record the position of the reticle on the grid. (I have this logged in my data book for each rifle.) I can then backcheck my zero by slapping on the Bore Sight and taking a quick read.
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  #2  
Old 11-12-2004, 01:39 PM
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Re: Bore Sighting & observations

Misaligned scope...rings...bases???

Kyle
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  #3  
Old 11-12-2004, 02:06 PM
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Re: Bore Sighting & observations

I don't believe it could have anything to do with the scope, base or rings because we take that type error out by adjusting the reticle to make allowance(s).

This shows up AFTER the rifle is zero'd. Shoot a little knot of rounds onto a 100 yard bullseye then check boresight and the barrel is pointed several MOA to the right of centerline??????

I've given thought that it might be a stress in the system somewhere, barrel steel, action threads???

I can't see anything at the crown so I don't believe it's there.

Just a little annoyance for me... I hate when something is too far off centerline on the bell curve without a good undertanding or explanation. What if whatever it is suddenly decides to get better, maybe right in the middle of my shooting???
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Old 11-12-2004, 02:09 PM
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Re: Bore Sighting & observations

Dave,
I beleive it's simply the barrel harmonics at work here. But an interesting test would be to have that barrel cryo treated, reinstalled, and rezerod to see if the results repeat. Then take the barrel off and set it back just enough so that the barrel would turn 90 degrees from where it is now and shoot it again and see if the misalignment goes up or down instead of to the side. But I can see where these results could be argued with having to recut the chamber and probably the crown in order to set it back properly. This alone could easily influence the results of this very non-scientific test.

Kyle, think about your answer. A scope hole/mount misalignment wouldn't cause this with Dave making the statment that the rifle is currently "sighted in". If the scope was set at mechanical zero and you looked down the bore and the crosshairs are off then yes that would be a true statement.
But once you adjust out any misalignment of the holes with the adjustments of the scope then that takes that issue out of the equation.
Regardless of the alignement in a perfect world, if your rifle is zeroed.... in theory your crosshairs and bore are pointed at the same spot X distance downrange, but your scope tube could physically be pointed to the left right up or down. That's why we have adjustable crosshairs.

Steve

P.S.
Dave,
I see we posted at the same time. I would probably rule out any stress also if your rifle holds a good zero through a heat cycle. and knowing you, you have already tested for that. So I think this would back up the harmonics theory.
Try a completly different load that shoots good enough to get a really good zero established and see if the centerline of the bore is pointed in a different direction or possibly right down the center.

BTW: good point about recording your true zerp point using your bore sighter grid. Simple solution, but never thought of that.

Steve

[ 11-12-2004: Message edited by: Steve Shelp ]
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  #5  
Old 11-13-2004, 12:58 AM
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Location: La Grange, TX
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Re: Bore Sighting & observations

Wild shot at it here. Barrel stresses in steel, more on one side than the other? Or the tube was turned not perfectly on center or something along those lines?

Or that old answer I've come to use after years in competition shooting, don't know why, dont have time to ponder it( could be loading ammo) and just adjust for it.

INteresting to know what your theory is?

Jeff
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  #6  
Old 11-13-2004, 06:01 AM
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Re: Bore Sighting & observations

Dave,
Remember that boresighting is static , firing the rifle is dynamic . With a lighter , more flexible tube you are probably more likely to see significant differences than with a heavier , stiffer barrel . There will be more barrel whip and no-one will guarantee that it will only be in the vertical plane . My Featherweight 7mm WSM does the same thing . Dead animals haven't noticed .Have a beer and forget it .
[img]images/icons/wink.gif[/img]
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  #7  
Old 11-13-2004, 07:33 AM
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Re: Bore Sighting & observations

Aussie

What kind of beer??? I wanna get it correct the first time. [img]images/icons/wink.gif[/img]
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