20 MOA base dilemma

R

Rob62

New member
Here is my situation. I put together a long range bolt action rifle.

The specifics are here in this separate thread I posted about the build.

http://thefiringline.com/forums/showthread.php?t=562774

Initial tests lead me to believe that with the scopes elevation knob turned all the way down the rifle will still shoot about 1.5-2" high at 100 yards.

Now I know this is a "Long Range" build rifle, but I still would like it to be able to turn the scope elevation knob down so that it could be dead on at 50-100 yards.

I do not see a work around to this situation other than removing the 20 MOA one piece base and going with a conventional base. Which of course would limit my long range capabilities.

I think I already found an answer to this issue or problem. That is to get a 15 MOA base. If that's wrong someone please let me know.

Your thoughts and opinions are appreciated.

Regards,

Rob
 
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That scope should have 77MOA of total elevation adjustment. So from zero (in the middle of one extreme or the other), it should have 38.5 MOA down and 38.5 MOA up adjustment. I don't see that you will have an issue. The 20 MOA base means you will only have 18.5 MOA of further down adjustment, after you adjust the elevation down 20moa for zero, which should be more than plenty. You should be able to zero the scope at 50 or 100 no problem. But it gives you that additional 20moa of up elevation for dialing in longer shots.

I have the same base on my target rifle and had no problems zeroing the scope at 100yds...
 
Sounds like a 15 moa base would let you get on at 100 yards. A 25 would be a step in the wrong direction.

Unlike precision shooter, your action, base, or scope may not put you in the center of the adjustments to start with.
 
Sounds like you have the scope with about 42 moa of adjustment. 10 or 15 moa rail should work, or Burris Signature Zee rings, or a scope with more adjustment range.
 
Something else is going on. A 20MOA base should only bias your zero towards the bottom of the elv range. You should be able to zero at 100 and still have some more down range. They are not supposed to bottom out your elv adj.

Ive got 20MOA bases on 3 of my bolt guns. All are zeroed at 100 and im in the bottom 1/4 of the elv range

All they do is give MORE room to go up
 
Thanks to all who responded.

precision_shooter - I believe your numbers. However I am NOW almost bottomed out in DOWN adjustments and still shooting high at 100 yards. So I am speaking from what is going on with my set up right now.

I think the most practical thing for me to do is go with the 15 MOA base and that will solve my problem without trying to further diagnose why the current results are what they are.

I'm ordering a 15 MOA base as soon as I can find the least expensive source for a decent one.


Rob
 
That's just odd. There is no way you should be running out of adjustment with that scope on a 20moa base.
Just for giggles, you do have the base installed correctly with it canting/sloping down towards the muzzle, right? The only two things I can think of that would cause you to run out of adjustment to sight in at 100yds:
1) base is installed backwards
2) internal issue with the scope

I would check your base and then call Leupold and talk to them to see if they agree that you will run out of adjustment at 100yds before buying another base.
 
Leupold VARI -X III, 6.5x20x50
According to an old Leupold catalog, it had 44 inches of adjustment at 100 yards. So, about 42 moa. 21 up, 21 down. Put it on a 20 moa base, and you're at the edge of the adjustment range.
 
I was in the "something must be wrong" camp until you said what the scope is. Now it at least mostly makes sense. I'm still surprised you couldn't eek out a zero with a 20MOA base, but it seems like you really do need a 10 or 15 MOA base.
 
Reading comprehension failed me on this one. This whole time I was thinking he has a VX not the older vari x...

So I stand corrected that your scope probably is out of vertical adjustment. My apologies.
 
Looks like you guys are all ASSUMING that the bore and top of receiver are perfectly aligned. I've seen plenty of standard rifle/base/ring/scope combinations that required lots of clicks to get lined up but seldom (never) see a perfectly aligned set-up right out of the package.
 
You're only short about 2 MOA to make it work, find the right thickness shim stock and get the base to 18 MOA. Measure the size of the base and you can even calculate what you need.
 
Looks like you guys are all ASSUMING
Click to expand...
Who's assuming anything? Rob62 showed a list of parts. Factory specs are available on the parts. He stated the results he's getting. The results match up real close with the specs.
 
SHARKBITE SAYS: All they do is give MORE room to go up
Click to expand...

Not really. Giving more room to go is NOT all they do. To keep new guys from being confused, I'll say this:

True, as you say............20 MOA bases give more room to go up, 20 MOA to be exact. But at the same time they reduce the ability to go down by 20 MOA, all other things being equal. They simply tilt the scope relative to the barrel. They don't do anything to the internal adjustment range of the scope.
 
From a purely technical standpoint that is true.

From a practical standpoint there is no reason to use any down adjustment past your zero. So any amout of clicks that you have "down" beyond your zero are wasted.

Granted your bullet will strike below POA at close range but its easier to hold high up close then to put in elevation adjustments.
 
"Who's assuming anything? "

How many scopes have you mounted that were perfectly aligned w/o using any adjustments? When folks start quoting the amount of adjustment vs the built in 20MOA base compensation, that's ASSUMING that all parts fit together perfectly creating perfect alignment with the scope's crosshairs centered.
 
Thanks again for all the comments. I don't want to shim the base as has been suggested. While I know there is nothing wrong with doing that, I just don't want to with this set up. Shimming seems, at least to me, as a sloppy fix - for this set up in this instance. I want everything as "right" as possible and going with the 15 MOA base will get me what I want to.

Rob
 
Just a follow up to kind of close out this thread. I ordered and received a 15 MOA EGW brand base. This base works perfectly with my scope and ring combination. I have about a dozen clicks of DOWN adjustments left on my scope with the rifle now sighted in dead on at 100 yards.

Again thanks for all the comments.

Rob
 
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