Gunsmithing What is best way to level scope to bore axis to avoid scope cant?

[GunDudeUSA]

Been reading about how scope cant can affect your point of impact the further out you go.

How do you level your scope so that the reticle exactly cuts through the bore vertical axis? The technique I've read so far is the following:

1. Establish plumb line some 10 yards away.
2. Look through your bore and align the middle to the plumb line.
3. Mount scope loosely.
4. Make sure scope reticle vertical line aligns with the plumb line.

Is there a better way (with better tools to help)?

 

[Country]

If I am reading you right you want to set up your scope and reticule in the vertical centre of the bore before sighting in .

This is how I do it . It may not be how the gunsmiths do it but it works for me .
Buy a shot saver the type that has a mandrel that goes into the bore.
I use a Tasco shot saver.
A plumb line gets you a vertical cross hair if the action is also vertical but it is not that good for centring as you can't line it up with the centre of the bore well .
If you sighted it through the bore you could get it reasonable but with my eyes I find using the shot saver is easier .
How you do it also depends on what type of mounts you have . Some can be adjusted left and right and some are fixed .

First centre the scopes reticule . Adjust the windage all the way to one side ( don't force it at the end when it starts to tighten stop ) . Then adjust it all the way back counting the clicks. Then click halfway back .

If your mounts are fixed and don't need lapping then the only jobs you really need to do is set eye relief and make the cross hair vertical and eventually centred enough to get on paper .
You can set the cross hair vertical with a plumb line or one of those gauges that you put across the back of the action .
If you use a plumb line the action has to be levelled first in a vice.
Once you get the eye relief right and the cross hair vertical you can firm up the mount ring caps .
Then using the shot saver rotate it until it is vertically parallel with the cross hair then you can adjust the scopes cross hair to be in centre both ways . That should get you on paper to sight in at the range.

For mounts that are not fixed and have sideways adjustments
Mount the gun in a vise so it is plumb .

Set up the scope with base side screws still loose but they hold the scope from slipping easily.
Adjust the scope until you can see the shot saver grid pattern . Get the eye relief right .
Plumb the scope reticule off the action or a plumb line and then parallel the shot saver grid off the scope reticule . They don't have to be in centre yet just vertically parallel . Once you do that firm up the ring caps but not fully tight.
Then tighten up the front mounts windage screws first a bit at a time left and right watching the cross hair on the grid to get it centred left to right speaking . Get the screws almost tight but not fully tight because you still want some give for the rear mount to centre and move the tube . Then do the same for the rear mount but watching that you don't move the cross hair off the same position . When the rear mount is almost tight test any variable power change . A good scope should change power and the reticule should not move from the same position .
If that checks out then a bit at a time tighten each side to fully tighten while still watching the reticule stays in the same position .
Only left to right is required .
Once you have the scope tracking up and down powers and staying in the same place on the grid and pretty close to the vertical centre you can lock up all the screws to fully tight .
I can get even cheap variable scopes tracking well with this system .
There is also another optical issue that can affect this process . If you do this setup with your head in an non normal shooting position then when your head moves to the normal shooting position it can make the reticule appear to be wrong , not vertical.
This is caused by the rotation of the eyes viewing position it can happen to some people with astigmatism of the eye .
So try to get your head in the normal shooting position to do the adjustments.

 

[Win_94]

I open my box magazine and use an "L" shaped square on the opening, (the lips are square to the receiver.) Then I aline the scope's windage cap to the square.

To test;
Make a target with a plumb line about 20 inches long with a intersecting line at the bottom. Then by lining the reticle with the intersecting lines, shoot a group at 100 yards. Then adjust your scope's elevation up about 18 inches,(enough to land at the top of your target,) and shoot another group with the same POA.
If your scope is square to the bore, the aspect of both groups will correlate with the line.

 

[cb_tikka]

Use a feeler gauge. Do a search as there are a couple of threads describing how to do it.

 

[-Claybuster-]

Use a feeler gauge. Do a search as there are a couple of threads describing how to do it.

That's how I do it as well.

 

[agbm]

Use this simple and quick : http://shop.milehighshooting.com/SPUHR-A-0080-81-Leveling-kit-for-separate-rings-SPUHRA-0080-81.htm

 

[ZiaHunter]

For rifles with a rail, I mount the rifle in a vise and use a Wixey digital level on the rail and level the rifle in the vise and secure. Prior to doing so, I have checked the scope for proper eye relief and mark the scope as reference point to the rings. I then mount the scope and use a cross hair laser level and project on a white surface far enough away where it can be clearly seen through the scope. I align the scope cross hairs with the laser lines as well as the eye relief mark on the rings. Gradually tighten the screws in a cross pattern until hand tight then torque to spec. I'll put the Wixey gauge on the elevation turret afterwards just to just to check. If you have a enough clearance between the rail and bottom of the scope you can use and adjustable parallel if not enough clearance you can use a feeler gauge.

 

[beercow]

I use a feeler gauge as well. You use it between the top the scope rail rail and the bottom of the scope. This method works for most high quality scopes, I tried it once for a buddy's el cheapo walmart special and the crosshairs weren't perpendicular to the bottom of the scope.

 

[mkollman74]

I use the feeler gauge method...