Besides a rifle, the most
important accessory for a varmint hunter is a telescopic sight. We call it a
scope, but it is important to remember that it is principally a sight. Many
shooters, your scribe included, have, at one time or another, spent more quid on
a scope than the rifle itself. Most of my scopes are Leupold, but lately I have
tried a few other brands such as Bushnell and Sightron and I am quite impressed
with both. I want to share my observations, as well as some scope problems that
have plagued me recently or questions I have seen on internet bulletin boards.
Since my problems might be your problems, let’s start take a look at what I have
learned, or in some cases, relearned, in the past few years about scopes.
Issue #1: I am shooting at
long range. I am using a Leupold scope with target knobs. I adjust my vertical
turret to raise the bullet impact, but my bullet impact is still low or has not
moved at all.
The other day I was shooting
one of my long range rifles at 700 yards. I wanted to try at 780 yards, so I
came up 10 clicks. I shot one bullet and drove downrange to see if I hit.
Seeing no new bullet hole in the target, I thought my allowance for windage must
have been wrong. I added some more windage and fired again. Again, inspection
revealed that I had missed the entire target. I repeated the exercise once more
before it dawned on me to look at my vertical target knob. The rotation counter
showed I was just above the fourth rotation – and also exposed the nature of my
problem. Leupold target knobs will move five rotations, but they only have 44
MOA of total adjustment, or 22 MOA from center in either direction (in a 6.5-20X
with a 1 inch tube). Each rotation is 60 clicks or 15 MOA, which means that
from center, or 2 ½ rotations, the erector tube is bottomed out at 22 MOA.
Since each revolution is 15 MOA, one full turn past optical center puts up at 3
½ rotations, and 7 (22-15 = 7) additional MOA puts us two clicks shy of the 4th
rotation counter. The scope knobs will still turn, but since the erector tube
is bumping against the scope housing, nothing happens. If you shoot at long
range, be sure you are not beyond the fourth rotation counter or are otherwise
outside of the scope’s adjustment range. And Leupold is not the only scope with
target adjustment knobs that turn after the erector tube has bottomed out. It
is the nature of the beast. In fact, Leupold scopes are among the best in terms
of total adjustment range (adjustment range is often sacrificed for optical
quality – more on that latter).
Now realizing my problem, I
decided to use holdover to connect. Since all of my long range scopes have
mil-dot reticles, I calculated the required holdover using this reticle, held
over, and hit the target.
The same problem occurred two
weeks later, with a different rifle. I was shooting in Arizona and ran out of
room when I went to 750 yards. I again used the mil-dot reticle to hold over
and then hit the target.
If you suspect that you have
this problem, the easiest way to confirm it is to slap an optical bore sighter
on your rifle, then move the vertical adjustment up. Does the reticle move down
against the bore sighter grid? (By the way, when you look through a boresighter
and move the vertical “UP,” it will move the reticle down, which forces you to
raise the gun to center the crosshair on the target.) If it does not, try
moving it the other way – it should up on the grid. If moving the vertical
adjustment up does move the reticle down on the bore sighter grid, you know the
erector tube is bottomed out.
As much as I love mil-dots, I
prefer clicking my vertical adjustment to connect at long range, so when I run
out of adjustment, something must to done to provide more elevation. The
solution to lack of vertical adjustment is to shim the scope, shim the rings, or
install a long range base. I prefer to use a long range base. These bases are
machined so that the rear is slightly higher than the front. Leupold makes
Redfield-type base that is tapered to provide an extra 15 MOA of vertical
adjustment. If you have a standard one-piece base, you can insert shim stock
under the rear portion of the base. Every .001 of shim stock provides about 1
MOA of additional elevation. Some shooters have had good luck shimming their
scope rings, but I don’t do it, as it ends up torquing the scope.
Issue #2: I read on the
internet that any use of scope shims will torque the scope.
If you use two piece mounts,
using shims under the rear scope is a bad idea, because the rear mount will be
higher than the front, and this will cause torsion if the receiver is
perfectly aligned and the bases are machined perfectly. If the receiver is
not perfect, then using a shim under a rear mount might just make a bad
situation better.
If you use a one piece mount,
then shimming under the rear the rear of the mount is okay. Theoretically, the
area of the mounting base under the second screw will now be very slightly
elevated and produce a small moment in the base, but I seriously doubt this
would translate into an induced moment, or torque, in the scope.
Burris has recently come out
with a new line of rings, dubbed the Signature series. These rings have
different polymer inserts that when installed, provide the same benefit as a
tapered base. Burris claims these rings have additional benefits.
Here is how they work. The
inserts wrap around the scope and come in halves. Each half is labeled; a “0”
insert is neutral, whereas an insert labeled “-15” will, when placed in the
bottom of the front ring, raise the bullet impact 15 inches at 100 yards if
combined with a “+15” insert on the top half of the front ring. You can also
move the scope left and right using inserts in the rear ring, only rotated 90
degrees.
Now, those of you who have been
paying attention might think, “Gee, that is really nothing more than shimming
the rings.” Well, these inserts are self-aligning, much the same way bearings
are self-aligning. The ring surface is convex, while the outside of the insert
is concave. The result is the ability to move the scope angle with respect to
the bore without inducing torque on the scope and all the while allowing a
shooter to keep the scope at or near its optical center. The idea is wonderful,
and makes a lot of sense. Guess what kind of rings I will try next time?
Issue #3: My scope
adjustments are erratic – vertical adjustment results in a windage change as
well, or a windage adjustment results in an unexpected vertical change.
I noticed this with one of the
rifles mentioned above – as I cranked on my vertical adjustment, I got some
weird windage shifts. The culprit is the same as Issue #1 – the erector
assembly is not even close to optical center, and the erector tube is riding
against the scope body tube. The erector assembly is a tube within the scope.
When you look through the scope and center the crosshairs on a target, you are
really looking through the erector tube, which together with its collection of
lenses, is often called the erector assembly. As you adjust the windage and
elevation, you are really tilting the erector tube up, down, right, or left,
which explains why crosshair is always constantly centered.
Problems occur when the erector
tube is tilted quite a bit in either the vertical or horizontal direction.
Suppose you go out to zero a rifle…the first few shots show you are perfect on
elevation, but you need to come way right, because your bullets are hitting way
to the left. You dial in a bunch of clicks to the right, which unloads the
spring holding the erector tube horizontally. Let’s say you dialed in enough
clicks so that the erector tube is almost touching the scope tube body itself.
You are going to have problems if you try and move the bullet impact up, because
the erector tube will start to ride the scope body. You will either run out of
elevation, or the windage will be erratic.
All scopes today use an erector
tube, and all scopes will have significant problems if the final zero places the
erector tube outside of the optical center. Even though many shooters like the
Weaver-style bases, I still have a soft spot in my heart for the old Redfield
type base, as it allows one to use the windage screws on the rear of the base to
zero for windage. This preserves elevation travel. The more windage travel you
use for your zero, the less vertical you will have in the field. Using a
Leupold 6.5-20X with a one inch tube, for example, you will lose ½, or 11 MOA,
of vertical travel if you use 11 MOA (44 clicks) to obtain the correct windage
zero. Of course, the Burris Signature rings will allow you to zero and stay
close to the scopes optical center, but instead of pitching the scope up and
down, we turn the insert 90 degrees and pitch the scope left to right.
Issue #4: Is there an easy
way to determine how far I am from my scope’s optical center?
Finding the optical center of a
scope is easy if you have a target scope, but if you don’t, here is a neat trick
from Garth Kendig at Leupold: turn the scope power to its lowest level, then
hold a mirror in front of the objective lens. You will see two reticles. Turn
the adjustments until the reticles are superimposed over each other.
Issue #5: Since I like to
shoot at long range, shouldn’t I select a scope that has 1/8 inch adjustments?
And along those same lines, why not select a scope that has a 4:1 power boost
instead of a 3:1?
These two “features” that at
first glance seem to be good deals deserve scrutiny if you are a long range
shooter. Let’s take these one at time…
When I shoot at 800 yards with
a scope with ¼ inch adjustments, one click on my scope moves my bullet impact 2
inches. My goal is to keep my bullets within 5 inches of my aiming point, so
you can see one click can make a difference, especially when it comes to
elevation changes (wind is such a problem at this range that coarse adjustments
are the least of my worries). If my scope had 1/8 inch adjustments, then I one
click would only move my bullet impact 1 inch.
This sounds wonderful, but if
you have a scope with 1/8 MOA adjustments, place it alongside a scope with ¼ MOA
adjustments. Look at the lines on the elevation dial of the 1/8 MOA scope…are
they closer together than those on the ¼ MOA scope? No. Okay, now look at the
rotation counter…does the 1/8 MOA scope have twice the rotations of the ¼ MOA
scope? No. Therefore, the maximum windage and elevation travel of the scope
with 1/8 MOA adjustments are going to be a lot less than the scope with ¼ MOA
adjustments. In fact, in identical scopes, the scope using 1/8 MOA adjustments
will, in general, have only half the total travel of a scope with ¼ MOA
adjustments.
Let’s look at the issue of
power boosts. Creating a scope with a power boost of 4:1 (4x to 16x, for
example) generally requires an erector tube with a wider diameter than a scope
with a 3:1 power boost. Hopefully you now know why this bad - a scope with a
wider diameter erector lens is going to have less total travel for windage and
elevation. For example, the Bushnell Elite 3200 series of scopes has a 3:1
boost, while their 4200 series has a 4:1 boost. You would think the 4200 would
be better for long range shooting, but you might be surprised to find out that
the 8-32 4200 Elite has only 20 inches of travel at 100 yards, meaning that if
you center the windage perfectly, you might be limited to putting the bullet 10
inches high at 100 yards, which means your maximum range using a 55 grain bullet
at 3600 fps is about 560 yards. Of course, Bushnell did this to reap the
wonderful clarity their 4200 series is famous for. You can always use a tapered
base to minimize the effects of limited travel. Some high-end model scopes have
more adjustment travel than their standard line. For example, the Burris
Signature 8-32X has 22 minutes of adjustment, while their Black Diamond in the
same model has nearly twice as much.
Issue #6: How can I tell how
much adjustment a scope has before I buy one?
By now you have seen one of the
most important considerations when buying a scope for long range shooting is the
maximum windage and elevation travel. Luckily, all the good scope manufacturers
receive good grades on making this data easy to access on their websites,
especially Bushnell. For the most part, adjustment travel numbers are minimums,
and many scopes will do better, sometimes significantly better.
Issue #7: Okay, I am zeroed
at 100 yards, but I did have to use some windage adjustment. Is there a way to
tell how far I can shoot in the field?
Here is another tip from Garth
Kendig. After you zero at 100 yards, run your vertical adjustment all the way
up and then take a few shots at 100 yards. Measure the distance from the aiming
point to the bullet impact, and then use a ballistics program to ascertain your
zero with the adjustments maxed out.
For example, let’s look at my
Savage Model 12 in .22-250. It sports a Bushnell Elite 4200 4-16x. Suppose my
load is a Hornady V-Max 55 grain bullet at 3600 fps. I want my reference zero
to be as far as it can such that my bullet trajectory travels no higher than 1.5
inches from the line of sight. That means I zero for 220 yards, or 1.3 inches
high at 100 yards. When I am done zeroing, I run the vertical all the way up.
I shoot a three shot group and discover my bullets hit 15 inches above my point
of aim. I now go into a ballistics program, configure the inputs so that the
zero at 100 yards is 15 inches high, and I can see how far I can shoot before I
run out of adjustment range. If you use RCBS.Load, the easiest way to do this
is set the “Sight-In Dist” to 100, then click the “S-I Vert Offset” spinner
button until it matches the number of inches between your 100 yard group fired
with max elevation and the aiming point (in my example that number would be 15).
Another good exercise once you
are zeroed is to lock your rifle in a rest (or have someone carefully hold it in
place) and then run your adjustments out, all the while watching what happens to
on a grid target at 100 yards.
Issue #8: Can’t I Just Use
High Scope Mounts to Obtain a Longer Zero?
Many shooters know that
mounting a scope higher above the bore increases the distance the bullet must
travel before crossing the line of sight, thus creating a longer range zero.
However, doing this is a poor way to add vertical travel. If we use the above
mentioned .224 bullet at 3600 fps as an example, raising the scope from 1.5
inches to 1.75 moves the longest possible zero from 690 yards to 750, or less
than two minutes of an angle in additional elevation. Less than two minutes
difference is hardly worth the expense of high rings, not to mention the other
problems associated with a high scope mount.
Question # 9: I like
changing my vertical adjustment, but I sometimes get confused where my zero
is…is there anything that makes this easier?
First, make sure you buy a
scope that allows you to reset the turret indicator. Bushnell, Leupold, and
Sightron all make scopes that allow you to reset the turret indication. I zero
most my rifles at 200 yards and then create drop tables that reference that
zero. What is very important to me is what I call the “second zero,” which is
the zero of my rifle after one revolution change. For example, let’s say we are
shooting a .22-250 that when zeroed at 200 yards, drops 104 inches at 705
yards. A drop of 104 inches requires 60 clicks, or 15 MOA, to achieve a zero at
that range. If I was using a scope that had 15 MOA per revolution, this means I
can quickly turn the scope one complete revolution to be zeroed at 705 yards.
Starting my count over again at ranges past 705 yards allows me to quickly move
from normal hunting zeros to long range zeros. Incidentally, this is one
advantage 1/8 minute adjustments have when hunting big game: a quick turn of the
dial on my Bushnell Elite 4-16X is worth 6 inches at 100 yards, which means I
can zero a .30-06 2 inches high at 100 yard, and then spin the dial one
revolution for a quick 400 yard zero.
Once you have identified your
close in zero (200 yards for me), you may wish to line out the rotation counter
lines below the one you use for your zero. That way you can quickly spin the
dial back down to your normal zero without having to count rotation lines. Some
scopes have rotation counter lines so close together this would be impossible.
Be sure to look before you buy.
I also tape a note on the stock
of the rifle and indicate the reference zero and the temperature at which it was
zeroed.
Question #10: Back when
variable scopes first came out, they had a nasty reputation for not holding the
same zero throughout the power range. This isn’t a problem anymore, is it?
A few weeks ago I took out my
Remington Model Seven in .300 SAUM for a little target practice in the Arizona
desert. The rifle is extremely accurate, but disappointed me when my first shot
at 700 yards was about 7 inches high. I thought it might have been caused by a
clean barrel, so I shot another. That bullet hit almost right on top of the
first. I thought I must be hitting high due to high temperature, although I
thought I had compensated for everything properly. I shot at my 615 yard target,
and again noticed I was high. A little frustrated, I clicked down to my 500
yard zero and shot at the 500 yard target. That bullet was high. I then
noticed that my Sightron 4.5-14X scope was turned down to 12X. Thinking nothing
of it, I cranked it back to 14X. Thinking my zero had somehow shifted, I moved
3 clicks down and took a shot at the 600 yard target. That shot was low by
around 5 inches. “Bingo,” I thought. “Maybe the zero on this scope shifts a
bit at 12X. To test it, I added my 3 clicks of elevation and dialed in my 700
yard zero. My shot hit a little to the right, but perfect elevation. I turned
the scope to 12X and fired – that shot hit about 5 inches high. I alternated
shooting at 12X and 14X and proceeded to shoot two groups, one about 6 inches
higher than the other.
I still have the Sightron scope
mounted on that rifle which is now my favorite big game hunting rifle, so my
story is no condemnation of that brand. When I click the adjustments, that
scope moves the bullet impact perfectly. I will live with a bit of zero
wandering, because it is steady as a rock at 14X and I have total confidence in
the adjustments. You know, thinking about it, I rarely shoot anything with a
variable power scope on anything but the highest or lowest power.
If you have any interesting
scope tips or questions, I would love to hear them. Please email me at
antanies@envoydevelopment.com. Have a great day shooting!
