"bottoming out" a scope

Buy a scope mount that has an angle to it, 20 MOA is the most common. The mount/base will put the scope at an angle compared to the center of the bore. Basically a scope's reticle is zeroed in the center of the scope tube, the canted mount moves the zero point lower in the tube, this results in more upward elevation being available.

Return scope adjustments to center. Add shims to get close to zero. Put* a shim from a soda can, in rear ring, under scope. Bullet will impact higher.

Google " bushnell shim guide" and "scope mounting instructions"

Burris XTR Signature rings are another option

http://www.burrisoptics.com/mounting-systems/rings/xtr-signature-rings

They come with inserts that allow adjustment of both elevation and windage depending on how they are installed. Kinda pricey though but a neat concept.

What kind of rifle and what kind of scope mount?

I've seen problems like this with barrel scope mounts that were made for straight barrels installed on tapered barrels. Or vice versa.

"Bottoming out" typically means shots were going high but the elevation adjustment knob/turret hit its lower stop at the "bottom" of its mechanical range before enough correction could be made. The opposite is "topping out" when shots are below point of aim and elevation adjustment is all the way up.

What target range were you using and which of the above happened? If elevation could not adjust up enough, you'll need what's called a "rail" that's angled down several MOA compared to the axis of your current bases. They're usually 10, 20 or 30 MOA sizes. This assumes your current bases are not reversed on the receiver. Or use
Burris bases and rings mentioned earlier.

Note that putting the scope Windage and Elevation adjustments to mid point in their mechanical range does not put them at the center of the scope's opticial nor mechanical axis in the mounting rings. Centering scopes is putting the inside movable erector tube holding some of the lenses in the middle of the fixed external tube, with the front objective lens and rear eyepiece, the mount rings clamp onto. There's usually more adjustment range to move bullet impact right and up from center. These adjustments move the erector tube's front end.

https://goo.gl/images/2uZv87

Laphroaig said:

Burris XTR Signature rings are another option

http://www.burrisoptics.com/mounting-systems/rings/xtr-signature-rings

They come with inserts that allow adjustment of both elevation and windage depending on how they are installed. Kinda pricey though but a neat concept.

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I had the same issue with my 1903A3 and used the Burris Signature Z rings with Posiline inserts to get more adjustment. Has the be the "Signature Z" model. The regular "Signature" model doesn't take the inserts.

Is there a chance the scope tube's front part is bent down?

TexasPatriot.308 said:

this is an old Remington 788 chambered in .308, thin barreled rifle. the scope is a new Redfield Revolution 4x12x40. I previously had a Nikon 3x9x50 on it and sighting in was no problem.

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Making assumptions and looking up new versions of both of those scopes, it appears the Nikon has an adjustment range of 80 moa and the Redfield only goes 50 moa.

If that is true, then the Nikon could hide a scope mount problem a bit easier.

chicharrones said:

the Nikon has an adjustment range of 80 moa and the Redfield only goes 50 moa.

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That typically means the maximum from limit to limit in elevation and sometimes windage, too. Where the zero point is at scope center reduces that by some amount depending on the physical limits inside the scope. A common limit is 30 to 40 percent of that from zero down to the stop and 60 to 70 percent from zero to the upper stop. Depending where the scope's adjustments are at for a zero with some ammo, that'll change. No scope has that limit from a rifle's zero to it.

What I do first is check to see if the rings are properly aligned with each other.

On most rifles, I use two piece Redfield mounts & rings. My next step is to center the reticle in the scope, both windage and elevation.

After centering the reticle, I use the windage adjustment of the rear mount to get the windage sighted in. If the group hits to the left, move the rear of the scope to the left. If the group is to the right, move the rear of the scope to the right.

Once I've got the windage dialed in, I zero the rifle using the scope turrets. When the erector set is too far to the left or right, it will limit erector set elevation travel because the erector set will hit the side of the scope tube

MistWolf said:

My next step is to center the reticle in the scope, both windage and elevation.

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Do you put each adjustment in the middle of its range of movement?

Yes. I run the turrets full left/right and up/down counting the turns and center each. For example, if it takes five full turns of the turret to go from stop to stop, I take the turret to one stop then come back two and a half turns

MistWolf said:

...if it takes five full turns of the turret to go from stop to stop, I take the turret to one stop then come back two and a half turns

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While that's the popular way, it's not correct. There's typically more range up and right than down and left. After doing this, look up close into the front objective lens. You can see the front if the inner tube appear off center. The back end of that tube is fixed exactly in the center.

Mechanical and optical zero is when the scopes inner tube is centered in the outer tube. Resting the scope in a cardboard box with V cuts for the scope to rest in. Best if V parts are further apart than shown, but you get the idea. Align the scope on some distant point. Twist the scope round and round while looking through it then adjust E and W knobs until the reticle stays in one place. Look into the front of the scope then see that inner tube well centered.

Another good way to find optical zero is to place the objective flat against a mirror, then adjust until both sets of crosshairs coincide. You have to do it in a brightly lit room, because all of the light has to come through the ocular. Best image is on low powers with variables. Fast and easy.

Counting the revolutions and dividing by two has always worked well enough for my purposes.

I know that the windage adjustment may not be equal to elevation. That's why I count the numbers of turns for each separately.

After using the spin the scope in the V notch method, have you checked to see if the adjustment from center to left was different from center to right, or if the travel from center to up was different from center to down?

Yes. But only to see what the limits are. They're often different from what advertising or specificstion data has.

And on the several scopes I've so zeroed, there's more MOA up and right from center. When that's done and scopes are mounted on rifles, they're very close to bore sight with the bore axis. My two 16X target scopes have twice the adjustment range up or right from centered than down or left.

All scopes I know of are set to center when shipped to retailers. Some have this correct way of zeroing in their instructions. You can also do it this way:



If the best you get has the reticle moving around in a one or two MOA circle or arc, one or both parts of the scope tube at the V points is a few thousandths inch out of round. One MOA on an 8 inch V block spacing is about .002 inch.

I use the mirror method. It's faster than counting clicks.

I'm glad you asked this question because I was going to before I found it. I have a old NOS scope. It was cracked way up on my 223. I moved it to my Barrett 50 BMG. The BMG has a 27 MOA rail. I bore sighted it at about 27 yards POI 2" low. Shot it today at that distance to find POI=POA. I cranked the turret all the way to the bottom which was about 2MOA Went out to 110 yards expecting POI to be 2" high but end up over 10 MOA. I haven't measured it yet but it's probably more like 15 MOA.

There is a small button, cap, or adjusting nob with a cross slot in the bottom right hand corner at the turrets I don't know what it's for. I was wondering if maybe it's an adjustment but afraid to mess with it.

I've never had a chance to shoot long range so I've always just shot them in & left it.

Bart B. said:

One MOA on an 8 inch V block spacing is about .002 inch.

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Thanks for this.

It worked out really close for me. I only have about 6" between rings. I needed 10 MOA so using your formula I added a .020" shim to the front sight & was good to go.

Close enough.