View anlge with 20 moa rail?

[Snootch]

I understand how the 20 moa rail works by angling the scope down but does that effect the field of view? I would think that if you looked through your scope you would loose some top field of view and if so how would you correct it if you can, adjustable cheek rest?

 

[7magcreedmoor]

Depending on your scope, you may not be able to tell any difference between a zero angle base or a +20 MOA. I use a 20MOA base and Burris ZEE with inserts, and my 200 yard zero is only 15MOA from the bottom of the elevation turret adjustment. Only on the lowest magnification can I tell that the reticle appears to be slightly off center. My intention when using an angled base and inserts is to have the scopes internal adjustments be as close to centered as possible for my longest shots, say 1000 to 1200 yards.

 

[Senderofan]

The canted base has Zero effect on your field of view. Yes...it tilts the scope...but when one zero's the scope...It would appear exactly the same as it would with a flat base. It does not affect the lenses or the view through them....but rather changes the elevation adjustment within the scope. It serves to free up internal adjustment for potential longer shots. It can also allow one to run the internal adjustment near the middle of the adjustment range....avoiding scope bind of the internals.

Depending on your round, your scope and the distances you want to shoot to.......the canted base can be very helpful. Some scopes may not have enough internal adjustment range....but most I've run across can handle a 20 moa base. Stepping up to 30 or 40 moa is another story.

I have 20 moa bases on all my centerfire rifles except my AR's. They work great!

 

[Senderofan]

I found one thread that said the rear of the base is 0.022" higher than the front on a one piece 20 moa base. It's not a huge dimension.....I suspect going from a 42mm front objective to say a 56mm would have a much greater impact on whether you'd need an adjustable cheek rest....because it would dictate a higher set of rings.

 

[Garycrow]

The difference in height of a 20 MOA base vs. the 0 MOA is less than 1 mm, it's irrelevant to cheek weld. They don't change the field of view at all on any setup I've seen. Perhaps there are some scopes with very small internal adjustment ranges where there would be a problem, or perhaps a rifle with a crooked barrel installation, but otherwise there's no practical difference between them and a 0 MOA base. If you're going to use a picatinny rail than there's no reason not to make it a 20 MOA.

 

[918v]

I think he meant the scope will lose FOV if the canted base forces you to bottom out the erector in order to zero the scope. Yes, that can happen on some scopes. That's why you should consider the elevation range and max distance before purchasing the scope.

 

[Senderofan]

I think he meant the scope will lose FOV if the canted base forces you to bottom out the erector in order to zero the scope. Yes, that can happen on some scopes. That's why you should consider the elevation range and max distance before purchasing the scope.

I guess he has a different definition of "Field of View".....since it's described as so many feet at certain distances when looking through an optic...... usually this can be found when looking at the specifications of optics. Basically how wide and tall the view is at specific distances. Canted bases will shift POA and POI from a non canted base zero and not change the size of the field of view....Is what I was trying to say. Guess things get muddy if we aren't all on the same page with terminology

I whole heartedly agree about the possibility of running out of internal adjustment for elevation when using a canted base. Many years ago I had purchased a new Burris 8-32x that had a 1 inch main tube. I could not zero that scope at 100 yards with a 20 moa base. I ended up selling that scope and getting a NightForce BR 8-32x ( this was back when the NXS line was just coming out )...and all was well.

Wayne

 

[FEENIX]

Depending on your scope, you may not be able to tell any difference between a zero angle base or a +20 MOA. I use a 20MOA base and Burris ZEE with inserts, and my 200 yard zero is only 15MOA from the bottom of the elevation turret adjustment. Only on the lowest magnification can I tell that the reticle appears to be slightly off center. My intention when using an angled base and inserts is to have the scopes internal adjustments be as close to centered as possible for my longest shots, say 1000 to 1200 yards.

+1!

Originally Posted by bruce_ventura
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.

 

[918v]

I guess he has a different definition of "Field of View".....since it's described as so many feet at certain distances when looking through an optic...... usually this can be found when looking at the specifications of optics. Basically how wide and tall the view is at specific distances. Canted bases will shift POA and POI from a non canted base zero and not change the size of the field of view....Is what I was trying to say. Guess things get muddy if we aren't all on the same page with terminology

We are on the same page.

On some scopes, when you crank the erector all the way down and bottom it out you lose FOV because some of the image (the outer edge) disappears.

 

[Snootch]

Thanks guys... Sorry about terminology, you guys gave me the answer I was looking for. I'm hoping to get some long range shooting in the near future. gun)