Rifle Scopes Canted Base / scope equation question

[padronanniversary]

I've searched, and did not find a formula or solution to this question so I was hoping that you knowledgeable hiders would be able to answer these questions and educate me on this a little further.

I have a S&B 5-25 which has 93 MOA of elevation.

How do you calculate which cant base one would need based off the following requirements

Running a 308 175 smk at say 2650
zeroing at say 100 yards
Shooting out to 1000 yards



The options would be 18 MOA, 28 MOA, or 45 MOA scope mount on a flat base

So according to my ballistic program I would need roughly 38.18 MOA to reach out to 1000 yards, and at 100 yards have zero, and at 50 have - .32 MOA.

So assuming a flat base (i.e. AIAW) what would be ideal ? It seems with 93 MOA range, I should be able to run without a cant to 1000 yards, based on a mechanical center of 46.5 of the scope (93 moa total elevation / 2)

Would someone please advise how to calculate the correct base (i.e. range of scope + base = moa at certain max distance)


Thanks in advance

 

[Lindy]

Re: Canted Base / scope equation question

You've basically answered your own question. With the S&B5-25, you won't need an angled base to shoot as far as you'd care to with a .308.

If you have some other application in mind, you followed the correct procedure, i.e., calculate the angle required to reach the farthest range you intend to shoot to. Then subtract that from half the scope travel.

If you get a positive result, you don't need an angled base. If you get a negative result, get a base angle sufficient to give you a positive result when added to half the scope travel.

You'll actually need a bit more than that, because you have to use some elevation to reach a 100 yard zero, but it's not a lot. You also want some safety margin, in case the base screws are not precisely parallel with the bore, and you have to use some windage to zero, which reduces how far the reticle will travel at the extremes of its range.

 

[kombar]

Re: Canted Base / scope equation question

Everything he said, but I'd also like to add that there aren't really any drawbacks using a base with built in elevation.

Optics perform their best when viewed through the center of the lens system. A canted base will give you better image quality where you'll need it the most, at long range.

If it were mine, I'd probably do a 28 MOA base, since that should center the erector somewhere around 800 yards.