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Sharpsman
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Joined: September 13 2007
Location: North Louisiana
Posts: 346
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| Posted: November 09 2009 at 8:31am | IP Logged
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I'd like to inject a little info here; just maybe I can add something or to maybe just say it in another way for clafification. If one were to go to the 100 or 200 yard line and get a DWZ aka DEAD WIND ZERO such that the rear tang is on MZ aka MECHANICAL ZERO (the rear tang sitting in the middle of the grid lines) and then go back to the 1000 yard line and shoot under the same no wind conditions....with a perfect hold and break...the shot (using a .45 caliber with say a 550 gr. bullet and having a right hand rate of twist) would probably impact somewhere betwixt 35" to 40" right of the targets center. This is because of rotational drift aka torque applied to the bullet by the right hand twist. Therefore to offset the bullets 'drift'....it's necessary to shim the right hand side of the sight base of the rear tang such that when a shot is fired it will offset the drift to a point striking the targets center. The old issue Buffington rear barrel sight was mechanically designed with a sliding feature such that the sight moved on an angle toward the left as it was progressively moved upward. I have all my rear tang sights shimmed under the right hand side of the sight base to a degree that when shooting from whatever yardline under a no wind condition that my rear tang setting stays at mechanical zero because the degree of angle as the eyepiece moves upward coincides with the degree of bullet drift such that the bullet impact is at center of the target! The degree of angle (or amount of shim thickness) required to accomplish this will vary due to the rifles make/manufacture and the degree that the rear tang is in alignment with the bore of the rifle's barrel! This rotational drift problem applies to all rifles used for long range whether they have right or left hand twist rifling aka if left hand twist....shim under the left side of the rear tang base!
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Kurt
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Joined: October 05 2007
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| Posted: November 09 2009 at 10:03am | IP Logged
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On all of my rifles I have my DWZ set for 300 yards with the sight staff set for that range and windage set to zero except one of the .44-90's that has a front wind gauge and that is set for 600 with the front and back all on zero.I spent a lot of time in the mornings at the Quigley working on the back base to get it where it's dead on before the winds start moving.
I don't think that there is a difference at the point of impact with the staff canted to allow rotation drift from 200 to a 1000 as long as the wind stays down.
The buffington on the trapdoor holds true just like my tang.
But regardless the wind very seldom is the same at all points down range.
My main objective with having my sights dead zero is to always go back to zero when the wind gets to fish tailing.
There is nothing more annoying to me than a sight that is hanging past the center of the dove tail It distracts my when I'm focusing on the front sight.
Kurt
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Guns only have two enemies: rust and politicians.
Anyone who is not a liberal in his youth has no heart. Anyone who remains so as he matures has no brain!"
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drcook
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Joined: October 05 2007
Location: Ohio, near Akron
Posts: 302
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| Posted: November 09 2009 at 8:32pm | IP Logged
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Problem is fixed. M.Z. is now where it should be. There is a point of impact change when I change aperture sizes in the Hadley, it might be off a couple .001's and there is a POI change between bullet weights. However, on my soule sight, my adjustments are .005 (1/2 minute) 2.5 minutes on a full turn of the dial. I can live with it being 1/2 minute off, and that was probably the wind.
Now to go through all the rifles and get them all corrected.
It is good we have this forum to discuss things on without all the political and other noise that goes on over on some of the other boards
dc
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We thought about it for a long time. And when we had thought about it long enough we declared war on the Union and I didn't surrender but they took my horse and made him surrender...Lone Watie
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Ranch 13
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Joined: March 13 2003
Location: =
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| Posted: November 09 2009 at 8:35pm | IP Logged
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Dave glad you got it worked out. Now can we talk about you rerouting summer vacation plans and bringing your child bride and her daughter to the Quigley and touring eastern MT and Wy? 
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The most expensive bullet there is isn't worth a plug nickel if it doesn't go where its supposed to.
GUSA #6 http://ranch13.blogspot.com/
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drcook
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Joined: October 05 2007
Location: Ohio, near Akron
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| Posted: November 09 2009 at 9:01pm | IP Logged
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Don,
I had to get it worked out or it would have driven me crazy. Like Kurt said that IF the front sight was off, it would have bugged him, it would have bugged me too. BAD. I have a quirk in my personality that if I do something, it has to be just right, And LOOK just right. I have a hard time doing things sometimes if I can't make them just right.
For example, we gutted the bathroom in our house (we live in a house built in 1949, that was sorta rigged) down to the studs. My dad helped. We shimmed boards to get everything just perfectly flat and level to put on the drywall. After mudding the joints and such, I worked on one corner for a couple days until I got the intersection of the lines from the ceiling and the wall to all be in line with a sharp square corner. Didn't matter that there isn't a flat, square wall in this house, that one corner that I worked on had to be perfect. The bathroom has the most perfect walls on the whole place.
And I would really like to end up on that side of the big old crick running down the middle of the country if the decision was entirely up to me. However, there might be room for a quick run that away this next summer.
dc
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We thought about it for a long time. And when we had thought about it long enough we declared war on the Union and I didn't surrender but they took my horse and made him surrender...Lone Watie
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Handloads.Com Forum : BPCR - Black Powder Rifle Cartridges
Topic: Field of View Shift
