Help me understand-scope elevation and rail cant - EDIT

[thefitter]

Two scopes - S&B 5-25x56 and MARCH 5-40x56

Same rifle, rail and rings. Rail has 30 MOA cant (if I'm remembering correctly) and the rings also have 20 MOA cant, so that's 40 MOA total cant.

Now I know is a lot of cant, but my question is why can I dial low enough to zero at 100 yds with the S&B but not the MARCH? I'm about 9" high dialed all the way down with the MARCH.

I am reading up on scope mechanics but I thought some of you gurus would know right off the bat.

Thanks

EDIT- Just found out that my rail has 30moa.

 

[snakepit]

Re: Help me understand-scope elevation and rail cant

There is a lot of experience on this forum and they will be able to help you more than I but I think that usually as you increase the max power of the scope you reduce the amount of correction available. Since the S & B goes up to 25 power and the March up to 40 power that could be the difference. Seems to me this is way over kill on the MOA for 100 yards. Also they say you should not use your scope at the maximum of your elevation or wind correction. What caliber are you shooting and how far out are you planning on shooting?

 

[thefitter]

Re: Help me understand-scope elevation and rail cant

There is a lot of experience on this forum and they will be able to help you more than I but I think that usually as you increase the max power of the scope you reduce the amount of correction available. Since the S & B goes up to 25 power and the March up to 40 power that could be the difference. Seems to me this is way over kill on the MOA for 100 yards. Also they say you should not use your scope at the maximum of your elevation or wind correction. What caliber are you shooting and how far out are you planning on shooting?

Both scopes are used to 1000yds. I agree that 40moa is technically too much cant, but I still want to understand the difference.

 

[M-61]

Re: Help me understand-scope elevation and rail cant

I think I understand your question but maybe not so keep that in mind.
I do not believe "CANT" is the correct word. I think that applies to the reticle not being truly parallel nor vertically true.(something to avoid)
However what does matter is different make scopes have vastly different amounts of elevation that is mechanically built into them thus available to the user. (also true for horizontal correction).
40 total MOA is alot of "UP" and a particular scope may not have the range to bring it DOWN.
I am not a scope expert but I hope this at least helps, and I am sure this question will bring some expert answers.

 

[thefitter]

Re: Help me understand-scope elevation and rail cant

Tried another S&B 12-50x56, and could zero it at 100 yds no problem.

Here is the elevation data on the scopes:

March 5-40x56 Elevation - 26 mils
S&B 5-25x56 Elevation - 24 mils
S&B 12-50x56 Elevation - 17.5 mils

Thanks

 

[mr45man]

Don't suppose it has a zero stop that might be the culprit
John H.

 

[thefitter]

Don't suppose it has a zero stop that might be the culprit
John H.

First thing I checked, but good call anyway.

 

[CatShooter]

Two scopes - S&B 5-25x56 and MARCH 5-40x56

Same rifle, rail and rings. Rail has 30 MOA cant (if I'm remembering correctly) and the rings also have 20 MOA cant, so that's 40 MOA total cant.

Now I know is a lot of cant, but my question is why can I dial low enough to zero at 100 yds with the S&B but not the MARCH? I'm about 9" high dialed all the way down with the MARCH.

I am reading up on scope mechanics but I thought some of you gurus would know right off the bat.

Thanks

EDIT- Just found out that my rail has 30moa.

First, the proper word is "TAPER", not cant.

Cant is when the scope is tilted a bit sideways, so then the cross hairs are vertical / horizontal, the rifle is leaning over to one side...

... and when the rifle is vertical, the cross hairs are tited to one side.

Shooter go to extrene measures to avoid ""cant".

"Taper" is when the mounts are thinner in front than in the back.

If you take a good quality scope that has a total elevation of 40 moa, and put it on a well machined action, and mount it with proper rings...

... you will have 20 moa of adjustment belowhe bore line, and 20 moa of adjustment above the bore line.

Now, the 20 moa of adjustment below the bore line is good, cuz it will raise the barrel 20 moa, and allow you to zero further out. BUt the 20 moa above the bore line is wasted, cuz it will drive the bullet down into the dirt.

And.. 20 moa of elevation is not enough to get you much past 500 to 700 yards with the average centerfire round.

So, we "taper" the scope mount - we make the front lower than the rear - we can do this by actually machining a taper into the base, or we can shim the base(s).. or do like Burris does with their signature rings, and use adjustable ring inserts to lower the front of the scope.

So, we put 20 moa of taper in the front of the scope - now, to zero at close distance, we spin the elevation turret all the way to the bottom. Now we have all 40 moa as usable "up", and we can get to 1,000 yds, and past.

BUT, (and this is a big one) if you have more taper than half of your scope travel, you will be able to zero at long range, but you will not be able to zero at close range.

50 moa of taper is a lot, unless you have a scope with 100 moa or more of total elevation.

I have all of my rifles set so the 100 yd zero is at the bottom of the elevation adjustment, and I use all of the available adjustment as "up".

 

[thefitter]

Thanks. I had a long talk with S&B today. I have a better understanding of whats happening within a scope. One of the critical pieces of info I received was that even though I was able to zero the S&B at 100yds with 50 moa TAPER that it was not good for the erector springs to be constantly at maximum compression. So I am either going to store the rifle with some elevation dialed or change the rail.