Setting Scope Windage Center

[CaptJim]

Wondering if anyone has had this happen:

For years I have used two methods of bore sighting. My favorite is to look through the bore at a target and align crosshairs accordingly.

The second is to use my old Bushnell optical bore sighter, which has done a good job.

Which one I choose depends on circumstances.

I just recently changed a scope from one rifle to another and since it was at night I used the Bushnell boresighter. The scope is a Bushnell LRTS 4,5-18 which is good quality and has tracked reliably. It is mounted on a Rem 700 SA with an EGW one-piece base and Warne vertical rings. ETA: Not Warne, but EGW matched rings. Memory fart!

I decided to center the horizontal adjustment by dialing all the way to stop and counting the total clicks to get back to the other side. I wanted to see if optical center and bore lined up closely. The total in this case was 256 clicks, so I moved the windage 128 clicks in the opposite direction to center the windage crosshair.

Looking through the scope at the boresighter's grid, the windage was off by 4 lines (each line represents aprox 4" @ 100yds, or 16" total. The scope is in Mils so it took 39 clicks to get back to center (.10mil/click).

Either the boresighter is off by that much; or the scope's windage travel is not the same on both sides of center; or the scope rail may be misaligned. I removed and replaced the scope on the rail and got the same results.
I've never had to make this much of a windage adjustment before with either bore sighting method.

I will shoot the rifle soon, zeroing at 100 and then take it out to 2 and 300 to see if the windage is that far off. My dilemma is if something is off, what would be the most likely cause? Just wondering if anyone has had this problem and can comment?

Thanks,
CJ

 

[Eagle Six]

3.9 mils at 100 yards would be 14.04". That is a bit off, but not uncommon. If the receiver mounting holes or factory, they are notorious for being off center, especially the rear. Also the holes in the rail could be off by a little bit. If the receiver holes were off a little bit, the rail holes off a little bit and the scope reticle off by a little bit it could add up to what you are getting or even worse. When you shoot for zero it could be off even more.

I have Leupold the has 39 MOA left and 37 MOA right, 45 MOA high and 39 MOA down. I expect any scope to be off a certain amount from dead center.

Also, unlike so many others I have never had much luck using the bore sighting gizmo's like you use, but apparently you are better at using one than I have been, so I rely on the old fashion method like you have by looking down the bore, well for bolt guns and AR type gas guns that works well.

When the sun comes up, you will be able to confirm or correct from the results you are getting from the bore sighter. If the results are the same you will still have 78 inches of windage correct on the short side, which may be ample for your shooting style and conditions.

I assume the rings are matched and they are firmly and correctly mounted to the rail. If they weren't you would most likely have a lot more off center than you have. At this point I would say there may be a combination from the bore sighter, receiver holes being off center and reticle not perfectly centered. it will be interesting to here your findings, but I have seen worse and didn't like it anymore than you do!

 

[AlNyhus]

First thing I'd check would be the receiver base holes for alignment.-Al

 

[BoydAllen]

I do my centering a bit differently. Some time ago I made a fixture that is basically a V block thing that I mount to the top of a tripod set to a height that allows comfortable work when seated. The Vs are covered with tape so as not to scratch the scope. The drill is to observe the motion of the intersection of the cross hairs relative to a fixed object in the distance, and make the needed adjustments so that when the scope is turned around on the Vs that the cross hair intersection does not move. If I can use the Burris rings that have offset inserts available, my next move is to mount the scope with zero inserts and shoot it at 50 yards, then I note how far off center (from my point of aim) my shots are both horizontally and vertically, and do a little math to tell me what inserts I should use and how their parting lines need to be oriented to bring my point of impact as close as I can to my point of aim. Then I shoot the rifle at 100 yards and if my math was correct, adjust the scope for final sight in. This is for factory actions. For custom actions I have had good luck simply lapping the mounted (not the insert type) rings before installing the scope.

 

[CaptJim]

Just as a side note, years ago I boresighted a Rem 788 .223 with the Bushnell tool. I aligned elevation and windage with the sighter's 100yd center and went to a friend's 100yd range. The scope was a Simmons 3-9X50 I got from another fellow for cheap.
I knew I would need a large target at 100yd since I didn't want to set up a shorter distance frame. I put up a 3'X4' paper with a standard target in the middle. Using a rest, I fired a shot.
The range was in woods so I had to walk close to see holes. as I approached the target I kept looking at the large white paper. I stopped about 20 ft from the target and carefully looked all around and at the target frame.Wow! no holes. I went closer and there in the black bullseye there was a hole!! I fired 4 other rounds that were not in the bull but within 1/2 to 1 inch from center. I never adjusted the scope again.
Ever since then, even tho it might have been a fluke, I have had a fair degree of confidence in the Bushnell sighter.
CJ

 

[CaptJim]

I have Leupold the has 39 MOA left and 37 MOA right, 45 MOA high and 39 MOA down. I expect any scope to be off a certain amount from dead center.

How would I check that the crosshairs are optically centered to be able to come up with this result?
ETA: Other than the v-block method above.

 

[Eagle Six]

How would I check that the crosshairs are optically centered to be able to come up with this result?
ETA: Other than the v-block method above.

I don't think there is a reasonably priced tool for that you can use at home. If someone has experience with one I would be interested. The figures I quoted are from the worksheet from Leupold Service center who recently returned the scope. Previously when that scope was returned from service the worksheet read 44 MOA left/33 right and 42 MOA high/41 low.

Same scope, 11 years between service. The first service it shows a total of 77 MOA windage adjustment and 2nd service only 76. 1st service showed elevation total of 83 MOA and the 2nd service 84. Tells me the erector was off center a bit from one service to the next. It also confirms to me there is a margin of error by factory settings and of course how much would depend on the factory. I didn't quote figures from other scopes because I don't know.

I did recently center the reticle of a low end Vortex scope and it was off 1/2 MOA in both windage and elevation. True zero on 100 yard paper was off a little over 1 MOA. That is about as close to perfect I have ever had and a really quick zero. However I do not know how far from optical center the reticle is. I also don't know how far off center the barrel is, the rail, or receiver screws, just know the stars and moon lined up for that one!!

 

[palo]

I have had this happen a couple of times and my problem was the rings. One set of TPS and another the vertical warne rings.
I switched the rings around putting the front ring to the back and back ring to the front and it helped .

 

[CaptJim]

I have had this happen a couple of times and my problem was the rings. One set of TPS and another the vertical warne rings.
I switched the rings around putting the front ring to the back and back ring to the front and it helped .

Thank you - I never considered this.

 

[Lone Hunter]

Look into a set of Burris XTR SIGNATURE Rings. They have the inserts that you can turn to correct the left to right if you can’t get your other rings to work.
This came from the description in Brownells Description.
By utilizing Pos-Align Offset Inserts in Signature Rings, you can virtually sight-in your gun without moving the scope adjustments. By keeping the internal optics centered, you'll see through the scope all of the clarity, sharpness, and brightness that the optics designers intended for you to see. The offset inserts also correct for any misalignment caused by receiver holes drilled off center, or the bases or rings being slightly off perfect center. And for you 1000-yard shooters, the need for expensive tapered bases or shimming becomes a hassle and expense of the past. Kit inlcudes one set of each .005, .010, .020.

 

[CaptJim]

Look into a set of Burris XTR SIGNATURE Rings. They have the inserts that you can turn to correct the left to right if you can’t get your other rings to work.
This came from the description in Brownells Description.
By utilizing Pos-Align Offset Inserts in Signature Rings, you can virtually sight-in your gun without moving the scope adjustments. By keeping the internal optics centered, you'll see through the scope all of the clarity, sharpness, and brightness that the optics designers intended for you to see. The offset inserts also correct for any misalignment caused by receiver holes drilled off center, or the bases or rings being slightly off perfect center. And for you 1000-yard shooters, the need for expensive tapered bases or shimming becomes a hassle and expense of the past. Kit inlcudes one set of each .005, .010, .020.

Ironically I used these years ago to get a 20 MOA cant on a 1" tube without the expense of a base, but it never crossed my mind to use them now.
Another excellent suggestion... Thanks

 

[CaptJim]

Well, I removed the scope and rings from the base, reinstalled the rings moving the front to the back and back to front and rotated the rings 180 deg. so the mounting screws were on the opposite side.
After this, looked through the bore sighter and the crosshairs were positioned exactly the same as before changing.
So - the rail and rings are a straight and true system. My opinion is that the receiver holes are mis - aligned. Might try the Burris rings.
CJ

 

[46and2]

Well, I removed the scope and rings from the base, reinstalled the rings moving the front to the back and back to front and rotated the rings 180 deg. so the mounting screws were on the opposite side.
After this, looked through the bore sighter and the crosshairs were positioned exactly the same as before changing.
So - the rail and rings are a straight and true system. My opinion is that the receiver holes are mis - aligned. Might try the Burris rings.
CJ

I've had several laser boresighter. If I take then out and rotate them several times and re-tighten they make a circle pattern on the target.
ETA, I lap my rings and bed my base on every rifle.

 

[AccelR8]

How would I check that the crosshairs are optically centered to be able to come up with this result?
ETA: Other than the v-block method above.

Lay a mirror on a table or workbench. Stand the scope on the mirror on it's optical bell. Look down through the scope and you should see the scope's reticle and a reflected image of the reticle. Adjust the scope until the two line up.

I read that years ago and have done it a number of times. It seems to work. I have noticed that optical center as achieved with this method is almost never the same as mechanical center, achieved by counting clicks. They're close but not the same in my experience.

I think the v-block method would be better.

 

[palo]

Well, I removed the scope and rings from the base, reinstalled the rings moving the front to the back and back to front and rotated the rings 180 deg. so the mounting screws were on the opposite side.
After this, looked through the bore sighter and the crosshairs were positioned exactly the same as before changing.
So - the rail and rings are a straight and true system. My opinion is that the receiver holes are mis - aligned. Might try the Burris rings.
CJ

Swap the rings around front to back but don't rotate them to see if that helps.
If not the burris xtr signature rings should work

 

[Fred Bohl]

Lay a mirror on a table or workbench. Stand the scope on the mirror on it's optical bell. Look down through the scope and you should see the scope's reticle and a reflected image of the reticle. Adjust the scope until the two line up.

This method or variations thereof works well up to about 16x scopes.

I prefer using a pair of ball bearing V-blocks (see picture below) so that the scope body is not damaged. A "zero center both windage and elevation" can be quickly and reliably be achieved. If your real fussy, put the V-blocks on a surface plate. Look at a white target and adjust for no movement at cross hair center when rotating the scope.