Scope zero problem

[tmuller]

I have sighted two scopes before that worked great but I am somewhat new and have a problem. I have a Leupold VX II 3-9x40 that I was trying to zero this weekend and I'm having a problem. I bore sighted using the laser but I could not adjust the scope down enough. All shots at 100 yards are roughly 3 inches high!! The screw on top of the scope will not turn further and I don't want to crank on it. I am using leupold dove tail bases and medium height rings. Should I change rings? This has never happened before...I have always had enough play to adjust either way if I need to change elevation for shot distance. What did I do wrong? How can I fix it? Thanks!!

[Jicko]

I have sighted two scopes before that worked great but I am somewhat new and have a problem. I have a Leupold VX II 3-9x40 that I was trying to zero this weekend and I'm having a problem. I bore sighted using the laser but I could not adjust the scope down enough. All shots at 100 yards are roughly 3 inches high!! The screw on top of the scope will not turn further and I don't want to crank on it. I am using leupold dove tail bases and medium height rings. Should I change rings? This has never happened before...I have always had enough play to adjust either way if I need to change elevation for shot distance. What did I do wrong? How can I fix it? Thanks!!

Take a pic of your setup. Generally you shouldn't have a problem @ 100yds. What rifle is that?

One thing to try is swap your front and rear rings.

[tmuller]

It's a wby 30-06 sythentic...needs a nicer piece of glass but I thought this would do for a bit. It's so frustrating thinking I can just turn this screw but it won't turn...ugh!!

[Prc329]

Base tightened down properly? Bases not installed correctly? Sounds like either the scope is mounted to high or the scope is some how angles up.

[Fjold]

Check:
1.)The part number for the bases are the correct one for that model rifle.

2.) The front base is mounted on the front ring and the rear base is on the rear ring.

3.) The rear base is seated all the way down on the action.

[tmuller]

I'll check this stuff again but I could swear that everything was tight, the proper parts, and installed correctly. I am however, definately not above mistakes.

Sounds like either the scope is mounted to high or the scope is some how angles up.

I was thinking that it might be to high and to get lower rings but it doesn't appear to be...I'll try and post pics...but there is nothing noticeably wrong in appearance to me i.e. no slant of scope, no gap between base and action, etc. I couldn't have asked for three better people to get advice from. Thanks!! Hopefully I can figure it out.

[bwiese]

Sometimes swapping rings or mounts (in a setup where front & rear rings and/or ring mounts are supposedly identical, of course) can help.

Also even if you get the scope to zero but it zeros a long way from the center of the adjustment range, you should consider shimming the scope mount. Ideally you take up the 'slack' in adjustment by getting the base in general alignment and then just fine tune the scope. You generally wanna keep the scope 'happy' by operating at or near its optical center.

A Burris 6-20X scope I had on my 700LTR (on Leupold base/ring setup) was ~11" high @100yds when scope was centered. I put a 0.005" piece of scope shim material under the rear scope mount and got much closer, and subsequently zeroed from there with fairly small adjustment.

Minor errors in barrel vs receiver angle, in scope bases and scope rings can all conspire together to throw enough bias in that sometimes shimming is needed.

[WeThePeople]

Leupold is helpful if you contact them.

I think the elevation & windage range is 56 MOA.

Do you get the whole 56 MOA elevation range? If you put the rifle in a "vise" and crank on the elevation knob, does the knob turn 56 MOA? Does the reticle move 56 MOA? If no to any of the questions above, send the scope back to Leupold.

Sometimes the knob or glass inside gets stuck. If you have to shake or bang the scope to reset the knobs or glass, obviously the scope needs to go back to Leupold.

Is the windage at either end of the 56 MOA range? If so, it can limit the range of elevation on some scopes? Put the windage back near the middle and see if you get the proper elevation.

If everything works okay, you can follow bwiese's approach or buy a rail (scope mount) that already has 10 to 20 MOA of angle on it.

Good luck.

[tmuller]

I will definately swap the rings front to back and see if this helps. This is some very good advice and I am appreciative. I think that I am way out of the center of the adjustment range though so...if

sometimes shimming is needed

does this look good

http://www.brownells.com/aspx/ns/store/ProductDetail.aspx?p=914&title=SCOPE+SHIM+KIT

I was thinking buy a pack of the .006 and apply either 1 or 2 under rear base. Does this sound like a good plan? How can I calculate how much shim is needed? Thanks for the help I hope this works!!

[bwiese]

I will definately swap the rings front to back and see if this helps. This is some very good advice and I am appreciative. I think that I am way out of the center of the adjustment range though so...if

does this look good

http://www.brownells.com/aspx/ns/store/ProductDetail.aspx?p=914&title=SCOPE+SHIM+KIT

I was thinking buy a pack of the .006 and apply either 1 or 2 under rear base. Does this sound like a good plan? How can I calculate how much shim is needed? Thanks for the help I hope this works!!

Probably so.

I don't remember the exact numbers but we can approximate here with similar triangle proportions... this is an approximation since if the scope base is inclined at a slight angle the vertex of the triangle is quite a few feet behind the shooter).

Let's assume our scope base is 3" long and is 'perfect' (i.e attached at an exact point and not the 1/2" length each base often is) and that at the rear of the scope there is no height above bore line. None of these are true, but over a longer range these effects reduce somewhat in the calculation and you
can get a good ballpark range.

Also, 100yds = 3600"... (Duh).

So, using proportions of similar triangles,

3600" length / 3" height = 3" scope base length / X.

Thus X = 3 x 3 / 3600 = 0.0025" (approx).

So, if you shimmed by 0.003" for round numbers you'd get back into the very edge of adjustment range. 0.006" should give you another ~3" back into normal, and 0.012" (two shims) should really get you pretty well into center of adjustment range.

Before shooting I'd get my scope centered, elevation-wise, again. Take the elev knob, run it out to the closest end, then (counting clicks) run it out to the other end. Run it back 1/2 the number of clicks you counted and you're in the middle.

Remount your scope w/shims and see where you are and go from there.

[tmuller]

Thank you very much Bill...useful information that will no doubt help. I appreciate all the sound advice and will check the mounts and possibly shim.

[aplinker]

Sometimes scopes go in the rings easily and everything sights up just fine, sometimes it takes some "adjusting". Any free motions and pieces that can be interchanged should be tweaked to find the right way to mount it. I've had a couple that just had to be tweaked a bunch to get it right.

A Burris 6-20X scope I had on my 700LTR (on Leupold base/ring setup) was ~11" high @100yds when scope was centered. I put a 0.005" piece of scope shim material under the rear scope mount and got much closer, and subsequently zeroed from there with fairly small adjustment.

Why would you bother shimming it down? That's like having a "built in" 11MOA base!

[WeThePeople]

My prior post was to help you quickly determine if the scope is the culprit. If you want to start fiddling with rings, mounts, and shims first...have fun.

[tmuller]

My prior post was to help you quickly determine if the scope is the culprit. If you want to start fiddling with rings, mounts, and shims first...have fun.

I will definately count the clicks 1st and make sure that the scope isn't the culprit...I just don't think it is...but will double check to be sure. Your post was informative and I appreciate your advice and most certainly wil apply it. I will try to "tweak" it and play with the parts as well...I'll give a report as soon as I get it back to the range. Thanks again for all the good advice!!

[WeThePeople]

As always, free advice is worth every penny you paid for it.