optical center of your scope.

[Sika Slayer]

I see most use a rail with eg 20 deg incline to keep their reticule more or less centered. I have enough travel in my scope to easily shoot as far as I wold like to shoot without any incline in the rail.
So what is the advantage of using a inclined rail ? I am using a 7mm Rem Mag with a VX6 3-18 and have no aspiration to shoot beyond 1000 yards.

 

[FEENIX]

IMHO, Bruce puts it best ...

Even though the scope adjustment range may be large enough to get to 1,000 yds, you should use a 20 moa base. That's because off-axis optical aberrations that degrade resolution increase with incidence angle. You should set up your rifle so that the incidence angle is minimized for long distance shots (where resolution matters most).

Assume the base is within +/-10 moa of alignment with the rifle bore. Let's also assume your bullet drops no more than 30 moa at 1,000 yds, and you like to zero your rifle at 100 yds. With a standard base, you would need up to -40 moa of adjustment to get to 1,000 yds. That means you need a total 80 moa of adjustment.

With a 20 moa base you would need up to -20 moa to get to 1,000 yds, but up to 26 moa to get to a 100 yd zero (worse case boresight alignment in each case). That means you need a total 52 moa of adjustment. With a 20 moa base, however, the incidence angle at 1,000 yds is 20 moa less, so the image will have less blur.

 

[Sika Slayer]

Thanks for reply,
Does the incidence angle effect apply to 1st and 2nd plane scopes to the same degree ?

 

[bruce_ventura]

Thanks for reply, Does the incidence angle effect apply to 1st and 2nd plane scopes to the same degree ?

Yes, because the aberrations that cause image blur happen in the objective lens.

 

[hybridfiat]

Thank you for that reply it is very helpful

 

[DocB]

I see most use a rail with eg 20 deg incline to keep their reticule more or less centered. I have enough travel in my scope to easily shoot as far as I wold like to shoot without any incline in the rail.
So what is the advantage of using a inclined rail ? I am using a 7mm Rem Mag with a VX6 3-18 and have no aspiration to shoot beyond 1000 yards.

In your specific case with no intention to go beyond 1000 yds, an alternative to a 20 MOA rail might be Burris Signature Zee rings. They are designed to be used with a flat or sloped rail and with the use of interchangeable ring inserts the MOA incline of your scope can be changed to match your situation and shooting style. They also have the advantage of being able to remove practically all errors encountered when mounting a rail or scope rings.

Go to Bruce's site, check out his Tech articles which go into scholarly and definitive detail regarding these errors. Good reading. He's always ready to offer help too. He's been a great help and friend to me. Check his site out.

DocB

 

[FEENIX]

Go to Bruce's site, check out his Tech articles which go into scholarly and definitive detail regarding these errors. Good reading. He's always ready to offer help too. He's been a great help and friend to me. Check his site out.

DocB

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