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Old May 11, 2013, 10:40 PM   #1
Rustle in the Bushes
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What MOA rail for my 308?

I was about to get a 20 MOA rail but I will be shooting at 100-500 yards- sadly mostly at 100 yards because it takes 2.5hrs for me to get to a place where I can stretch out.

I am second guessing getting the 20 because I am worried that when at 100 yards I will be at the edge of my scope adjustment and thus wont be getting very good optical quality. What you folks think?

scopes a viper 6.5-20x with 65 MOA of elevation adjustment
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Old May 11, 2013, 10:49 PM   #2
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I know a lot of people seem to say 20 MOA or so, don't know why.

I have shot a heck of a lot of 1000 yard matches, and other long distance and never felt the need.

Using 243, 308, 30-06 and 300 WM I use normal Weaver Bases on my Winchester and never hand a problem.
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Old May 11, 2013, 10:59 PM   #3
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Assuming you're already using a decent long-range scope (which already has the range of adjustment needed to handle the range of adjustment for the distances at which the rifle will be used), the point of a range-compensated rail is to keep the scope's reticle in the center of the adjustment range and therefore in the optical sweet spot.

Putting a range-compensated rail on a gun and then using it to shoot at ranges that don't require that compensation is counter-productive. It means that you are now having to adjust your scope back down to compensate for the unneeded range compensation. That means you're moving the scope's reticle out of the center of the adjustment range.

So not only are you paying for something and then adjusting your scope to make it seem like it's not there, you're actually hurting yourself in terms of keeping the reticle centered in the adjustment range.
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Old May 12, 2013, 01:27 AM   #4
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My Ballistic calculator Results says with that scope you should have enough adjustment to shoot almost 900yds with no MOA cant

. You will not be close to maxing that scope out with a 20 MOA base . You would still have 12+ MOA left . Thats almost one complete rotation of your turret . I would put the 20 MOA rail on it but you really don't need it .
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Old May 12, 2013, 09:59 PM   #5
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keep in mind that a 20 degree mount will raise the eye piece of your scope noticeably so it changes your cheek weld. I like the scope mounted as low as I can get it so the 20 degree mount really irritated me for that reason. I have a Bushnell 4200 Elite that is not known for having a lot of elevation adjustment. Even with that the 20 deg mount is not needed with a .308 for 500 or 600 yards.

Last edited by Rumpelhardt; May 12, 2013 at 10:06 PM.
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Old May 13, 2013, 12:49 AM   #6
Rustle in the Bushes
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thanks for the answers folks. Not worried about cheek weld I have solutions for that cheers

So Ill prolly go with a 0 or 10- how does that work, will that mean my scopes zero will end up around 100 yards?? I guess that would depend on ring height, right?

Anyways Ill go with a 0 and that should mean Im using the optical best of my scope for the 100-500 yard ranges with a capability to dial up if needed right?
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Old May 13, 2013, 06:55 PM   #7
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Angled rails came about when those new fangled internally adjusted target scopes were used on match rifles used in 1000 yard matches saying good bye to the externally adjusted ones. A 20X scope may have a 40 MOA adjustment range; that's about 20 MOA from optical zero up, down, left and right.

With a a 30 caliber magnum needing 30 MOA above boresight to hit center at 1000 yards, that scope won't cut the mustard nor give enough elevation to do the job. So an angled rail was invented to take Weaver scope rings. (Jack Davis, gunsmith and NRA Referee at the Nationals made some of the originals). The first ones were 20 MOA but subsequent ones are more or less. They were originally called a Weaver rail. But nowadays it's a Picatinny rail.

One other thing such rails do. They put the scope's optical/mechanical axis better centered in its range so any alignment error between receiver axis and scope axis can be corrected for. With some scopes having less windage adjustment range at their elevation limits, a rail solves that problem.

To pick the one you want, find out what the range minimum and maximum you'll shoot at and the elevation above bore sight needed to do it with yor ammo. Then pick a rail whose angle splits the difference; erroring on the high side if needed. If your scope has enough elevation adjustment to boresight on a 20 MOA rail, that' good. If not, you may need a 30 MOA rail.

For use up to 500 yards, a 10 MOA rail will be best for your scope's optics and mechanics. The optical quality loss at the adjustment limits are insignificant; it's the uniformity of click values in the middle of the adjustment range that are better.
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Last edited by Bart B.; May 13, 2013 at 07:00 PM.
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Old May 13, 2013, 07:56 PM   #8
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Bart is technically correct but assumes that receiver, base, and scope are all straight, square, and level. Not all are. Your 100 yd zero might call for adjustment in any direction from center. I have owned a couple of rather crooked actions.

I think a flat rail will do you. A .308 match load is only about 15 moa comeup from 100 to 600 yards.
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Old May 14, 2013, 06:14 AM   #9
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JohnKSa gave you good advise. For the ranges you plan on shooting a raiser would be counter productive.
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