Bore Sighting & observations

[Dave King]

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.

 

[5Redman8]

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

Kyle

 

[Dave King]

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???

 

[Steve Shelp]

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 ]

 

[rost495]

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

 

[Aussie]

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 .

 

[Dave King]

Aussie

What kind of beer??? I wanna get it correct the first time.

 

[Steve Shelp]

Dave,
Another real obvious thought that crossed my mind last night.... is a bent barrel. Ask any of the good smiths how many perfectly straight barrels they have even seen? My current 1000yd BR LG barrel had 4.5 thousands of runout in it. This is not uncommon from what I've seen.
I also know of a barrel from a very prominent maker that had more than .010" of runout in in right out of the box. The shooter did his own work and physically tried to striaghten it the best he could in the lathe with another large bar for leverage. The same barrel cleaned my clock at the last NC match of the season. It will shoot!

It wouldn't take much to cause a 2-3 MOA offest at any distance. I know if your front and rear rests are 24" apart, moving your rear rest .0006" in any direction will move your POI 1" in the oppssite direction at 1000yds. So at 100yds that would be .006" of movement would equal the same 1" of movement. Translate that to a 24" barrel with .006 of runout, and you might have an answer to your "problem".

Or like Aussie said... if your happy with the accuracy of the rifle as it sits right now... I would go with the beer or 12 option also. Brand doeasn't matter after the 6th one anyway... though Yeungling is my personal favorite.

Steve

 

[4ked Horn]

Just a thought dave. Have someone else shoot your rifle without telling them why. If they shoot where the bbl seems to be pointing as opposed to where the scope is looking then the problem may be you. Maybe the stock dosent fit right or you are bracing after the sear breaks or some other quirk you have with this gun causing you to pull the shot left albeit a very consistant pull. With enough practice even a flinck can be consistant. Thats one reason why we own adjustable sights.

 

[Dave King]

Several goods suggestions here but I believe Steve is probably correct in one or more of his suppositions.

I have a pile of rifles and this one is the only one that points somewhere other than at the target as far as the vertical plane is concerned.


Oops, Aussie too, he's correct... beer works.

[ 11-14-2004: Message edited by: Dave King ]

 

[Ian M]

Dave,
You need to get you mind off this little situation - the only logical thing to do is to get on the phone and order another rifle

Believe we need to discuss your upcoming new tactical style rifle that you don't know about yet...

 

[Dave King]

Ian

That got me sitting up straight!! What new tactical style rifle????? Rifle, Rifle, Rifle, come-on... tell me about it.... I cant read!!!

 

[gonehuntingagain]

Your new tactical rifle will have to be built such that it will be able to take full avantage of your new ultra reliable user-modifyable scope that you created. That way it should be able shoot 2000 yards easily!

 

[Aussie]

Dave ,
So long since I was in the U.S. I can't remember for certain which beers I liked (I think it was the cold ones) . No matter , I'm sure they all have the same medicinal properties .
If that doesn't work you gotta get rid of that gun and replace it with 3 others .