Hi guys. I wrote this up a few weeks ago to summarize some stuff I've learned in the last couple years with regard to rifle optics. Hope it helps some people.

If you disagree, have corrections, or suggestions, let's hear 'em!

UPDATED 11/27/2007:

The version posted here is old, posted in 2005. This article has been updated and for over a year has been part of a 3-article series:


article | Practical Long-Range Rifle Shooting, Part I - Rifle & Equipment


article | Practical Long-Range Rifle Shooting, Part II - Optics


article | Practical Long-Range Rifle Shooting, Part III - Shooting


The OLD, ORIGINAL ARTICLE FOLLOWS



OPTICS FOR PRACTICAL LONG RANGE RIFLE SHOOTING

(C) Copyright 2005 Zak Smith All Rights Reserved

Reproduction or Republication by express written permission only

apollo.demigod.org/~zak/DigiCam/ITRC-2004/small/135_3506_img.jpg

(Schmidt & Bender PMII scope with 13 mils elevation, 0.1mil clicks, on a Remington PSS rifle.)

What is Practical Precision / Long Range Rifle Shooting?

Practical precision rifle shooting involves engaging small and/or distant targets at the limit of
weapon, ammunition, and shooter capability under time pressure in field settings.

Applications include but are not limited to: very small targets 1/4"-1" at 100 to 200 yards,
so-called "cold bore" shots, arbitrary unknown distance targets, shooter/spotter communication, and
combinations of all of those under time constraints.

Generally, these include everything a rifleman is likely to find in any "sniper", "tactical", or
"field" rifle match. The typical platform is a bolt action rifle, though an autoloader of
sufficient accuracy and appropriate caliber can do the job with some tradeoffs.

For our purposes, consider "long range" to mean within a few hundreds yards of the load's
trans-sonic boundary (the point at which the bullet slows to the speed of sound, Mach 1). For
example, with typical 308 loads and rifles, we are interested in ranges from 25 yards out to about
700-1000 yards.

#############################################################################################################

Ballistics Background

Some understanding of bullet trajectory and the physical factors affecting bullet flight is needed
as background before discussing optics.

In the simplest case, take an accurate rifle with sights zeroed at 100 yards shooting one type of
ammunition. In the absence of wind or shooter error, the bullet will impact the point of aim (POA)
when the target distance is 100 yards-- hence its "zero" is at 100 yards.

The "line of aim" is a line straight from the shooter's eye, through the sighting device, to the
target. The bullet starts off below the LOA by the distance between the center of the sighting
device and the center of the bore. This is called the "sight over bore" distance. The axis of the
bore is not parallel to the LOA-- the bore is angled slightly upwards. This causes the bullet to
start off with some "upward" velocity. As it flies down-range, it rises to meet the point of aim
(POA) which is where the LOA intersects with the target.

Depending on the bullet's velocity, the bullet might keep rising above the LOA and again intersect
with it a second time as it falls. Alternatively, it may rise just enough to meet the LOA and then
start to fall again.

demigod.org/~zak/firearms/optics_1.png

In this graph, two loads are displayed. The green trajectory is a 308 load zeroed at 100 yards. It
starts 2" low, rises to the LOA at 100 yards, and then drops off the graph 8" low at 267 yards.

The red trajectory is the same load zeroed at 200 yards. It starts 2" low, intersects with the LOA
the first time at about 40 yards. At 120 yards, it's about 1.6" above the LOA, then drops,
intersecting the LOA again at 200 yards. This is the second, or primary, zero. At 300 yards, it's
about 7" low.

Looking at the graph with the 200 yard zero, the point of impact (POI) at 100 yards would be about
1.6" above the point of aim (POA). At 240, the POI will be 2" below the POA. At 300, the POI will
be 7.5" below the POA. Thus, to hit a small target at 300 yards, the shooter would have to hold 7"
above the target. The bullet continues to fall relative to the line of aim as target range is
increased.

A table can be constructed which relates the drop distance for every range out to the maximum
engagement range. An abbreviated table might look like this, for a rifle with a 100 yard zero. (An
actual table would have intermediate distances like 120, 140, etc.)

RANGE   DROP
 100     0"
 200     2.87"
 300     11.2"
 400     25.6"
 500     46.9"
 600     76.0"
 700    114.9"
 800    161.7"

This is helpful, but the shooter is left with the problem of how to aim 47" higher than the target
when the distance is 500 yards. There won't be a 47" yardstick sticking out above the target.
Aiming the cross-hairs at a point imagined to be 47" above the target is difficult and very error
prone.

Angular measurements

Instead of measuring hold-over in terms of linear distance (inches or cm), it would be helpful to
translate those linear distances into units of angular measure. The concept of angular measure is
that an angle of 1 degree demarcates 1.7 yards at 100 yards, or 3.5 yards at 200 yards. Everyone
with a basic understanding of geometry should understand how angles work.

There are two units of angular measurement commonly used in rifle scopes. The first is the "minute
of angle." Dividing a circle into 360 degrees, then each degree contains 60 minutes. One MOA
demarcates 1.0472" per 100 yards of distance.

The second is the "mil". One mil is one part transverse per 1000 parts distance. In units we
understand, 1 mil is 3.6" per 100 yards (ie, 100 yards is 3600", one thousandth of which is 3.6").
Consequently it's also 1 yard at 1000 yards. Alternatively, in metric, 1 mil is 10cm per 100
meters, or 1m at 1000 meters.

Wind

Just like the atmosphere pushes on the bullet as it moves forward, slowing it down, any winds
present in the bullet's path can affect its trajectory. The most common effect is the cross wind. A
10mph cross wind will move a typical 308 bullet about 6" at 300 yards. The following graph
demonstrates the wind deflection as range increases for a left or right 10mph wind.

demigod.org/~zak/firearms/optics_2.png

Just like the drop table, we can generate a wind table, which might look something like this:

RANGE  DRIFT for 10mph cross
 100    0.6"
 200    2.6"
 300    6.0"
 400   11.0"
 500   17.8"
 600   26.5"  
 700   37.5"
 800   50.9"

Lead

For moving targets, the shooter must aim in front of the target a distance which depends on the
target distance and speed. This is called "lead." We'll generate a table for some standard target
speed and add it to our table.

Both the "drift" and "drop" values in the tables can be translated to use angular measurements (MOA
or mils) instead of linear measurements (inches or cm) to aid utility.

Typical Data Card

The shooter might end up with a data card that looks something like this. The first line describes
the load so he can keep straight what the data-card describes. The second line reminds him what
each column means.

155 LAP: 2825fps 100yd 0'
RANGE   elev wind   4mph->(MOA)
  25    4.00  0.25   6 moa
  50    0.75  0.25   6 moa
  75    0.00  0.50   6 moa
 100    0.00  0.50   6 moa
 125    0.25  0.75   6 moa
 150    0.50  1.00   6 moa
 175    1.00  1.00   6 moa
 200    1.50  1.25   7 moa
 225    2.00  1.50   7 moa
 250    2.50  1.50   7 moa
 275    3.00  1.75   7 moa
 300    3.75  2.00   7 moa
 325    4.25  2.00   7 moa
 350    5.00  2.25   7 moa
 375    5.75  2.50   7 moa
 400    6.50  2.50   7 moa
 425    7.25  2.75   7 moa
 450    8.00  3.00   7 moa
 475    8.75  3.25   7 moa
 500    9.50  3.50   7 moa
 525   10.25  3.50   7 moa
 550   11.25  3.75   7 moa
 575   12.00  4.00   7 moa
 600   13.00  4.25   8 moa
 625   13.75  4.50   8 moa
 650   14.75  4.75   8 moa
 675   15.75  5.00   8 moa
 700   16.75  5.00   8 moa
 725   17.75  5.25   8 moa
 750   18.75  5.50   8 moa
 775   20.00  5.75   8 moa
 800   21.00  6.00   8 moa

Columns:

1. Range

2. elevation for #1's target distance, in MOA

3. wind for #1's target distance, in MOA

4. lead for #1's target distance, in MOA for a target traveling at 4mph (a medium walking pace)

All the trajectory values can be calculated using one of the modern small-arms ballistics calculator
programs, such as Sierra Ballistic Explorer, Exbal, QuickTarget, Agtrans, etc. Several parameters
are critical to their accuracy: (1) bullet ballistic coefficient (BC) values, (2) accurate measured
muzzle velocity from a chronograph, (3) solid zero distance, and (4) accurate environmental
conditions including station pressure, temperature, or density altitude.

Trajectory Effects Of Dialing Elevation

The following graph shows the effects on bullet path of dialing elevation. The red trajectory
is with a 100 yard zero. Next, the shooter wants to engage a target at 400 yards, so he dials the
elevation specified by his data-card for 400 yards, which results in the green trajectory. He
repeats the same procedure for 600 yards (dark blue), 800 yards (purple), and 1000 yards (cyan).

demigod.org/~zak/firearms/dial.png

The following graph show the same trajectories, but with the bullet path converted to Minutes of
Angle (MOA) above Line of Aim. Observe that the MOA difference between the lines is constant as
distance is increased (the lines are "parallel"). This means that regardless of the zero distance
dialed, there is the same angular difference between any two zero distances (e.g. 400 vs. 600 is
approx 6 MOA.

demigod.org/~zak/firearms/dial_moa.png

Data Confirmation by Shooting

It is important to verify computed data by actually shooting targets at various distances and
looking at the actual hits (or misses) to determine if the elevation values are correct. Shooting
known-distance targets every 100 yards out to the maximum range is a good way to do this.

Desired Sighting System Capabilities

Let's look at the things we want to accomplish with the rifle sighting system:

1. Precisely specify drop hold-over out to our maximum engagement distance.

2. Precisely specify wind drift out to our maximum engagement distance.

3. Precisely specify target lead for moving targets/shooter.

4. Range targets of known size when Laser Range-finders are not appropriate

5. Observe target area

6. Retain #1-5's capabilities in low light conditions



#############################################################################################################



Optical Considerations

Magnified rifle optics have several salient optical properties which we need to understand before
discussing the capability trade-offs later:

Parallax Error

Parallax is the error in apparent POA vs. actual POA due to misalignment of the shooter's eye
vs. the scope's axis. A scope can be set to be parallax error free at one distance. A scope
either has adjustable or fixed parallax. Fixed parallax means the distance at which there is no
error is fixed to something like 100 or 200 yards from the factory. Most tactical scopes have
adjustable parallax, which means the user can adjust the parallax error free distance on the fly
to reduce parallax error whatever the current target's distance.

First Focal Plane vs. Second Focal Plane Definition

Variable-magnification optics can have a first focal plane (FFP) or second focal plane (SFP) reticle
configuration. A first-focal (FFP) reticle's features always demarcate the same angular
measurement regardless of the scope magnification setting. The reticle will appear to "shrink"
and "grow" with the target area as the magnification is adjusted.

A second focal plane (SFP) reticle demarcates angular distance that depends on the scope
magnification setting. The reticle appears to stay constant as the target area shrinks and grows
as the magnification is adjusted.

A fixed power optic is FFP by definition.



#############################################################################################################



Capability Tradeoffs

With the background out of the way, What are the capability trade-offs of the different feature choices?

Elevation Adjustment Methods

Elevation specification can be done by external knobs (or direct mount adjustment, e.g. the
Elcan), via reticle features, or a combination.

Knobs: If the primary method of specifying elevation is by external knob, the knob will have
"click" values. Each time the knob "clicks" to the next setting, the elevation setting will be
changed by the click amount. Typical values of clicks are 1/4 MOA, 1/2 MOA, 1 MOA, or 0.1MIL.

apollo.demigod.org/~zak/DigiCam/AI-AWP/small/154_5422_img.jpg

(Leupold 3.5-10x40mm M1 scope with 1/4 MOA-click external knobs, mounted on an Accuracy
International (AI) AWP)

Elevation Travel

The scope's internal mechanical design and the scope mounts used determine the maximum range for
which elevation can be specified. In the specifications for a scope, the maximum elevation
travel is described as something like 60 MOA, 80 MOA, 100 MOA, etc. This is the total "top to
bottom" travel of the erector assembly inside the tube.

If the rifle and mounts are level, the elevation adjustment should be in the middle of its total
travel when zeroed. For example, if we start with "0" at the bottom, a scope with 60 total MOA
elevation will likely be zeroed at about 30 MOA up from bottom, and cranking it all the way up,
it would stop at 60 MOA. In this case, the scope is limited to 30 MOA "up" elevation from
center/zero. This will limit the maximum engagement range by limiting the elevation setting that
can be dialed. For example, if a certain 308 load needs 31.5 MOA elevation for 1000 yards, the
described scope will not be able to dial enough elevation. When it hits its maximum at 60 (30
above center/zero), it will still be 1.5 MOA "short."

The way to get around this is to use an inclined scope base. An inclined scope based has some
downward "slope" built in. An inclined base with 20 MOA angle will shift the zero point in the
scope further away from its top extent. For example, with the 60 MOA scope described before,
instead of being zeroed around +30 MOA (its center), it would be zeroed at about 30 - 20 = 10 MOA
up from bottom, and have about 30 + 20 = 50 MOA "up" elevation left. Now instead of running out
of elevation travel trying to dial 31.5 MOA, the scope will dial freely up another 50 MOA-- when it is
dialed to 31.5, it still has 18.5 MOA left for dialing to longer distances.



Elevation Adjustment "Click" size

The smallest elevation change possible using the scope's mechanism will in part determine the
smallest target for which we can specify hold-over at an arbitrary distance.

For example, if we have a scope with 1 MOA clicks, at 400 yards that will demarcate 4.2", so it
will not be possible to dial the correct elevation to hit a 3" target at 400 yards with this
setup. One adjustment setting might be just under the target, and the next would be 1" high over
the top of the target.

The tradeoff of fine clicks is that more of them are required to achieve the same elevation
adjustment. For example, if 15 MOA are required to get to 600 yards, that would be 60 1/4-MOA
clicks, but only 15 1-MOA clicks. The large, coarse click values can be faster to adjust in the
field, at the expense of fine-grained adjustment ability.

apollo.demigod.org/~zak/DigiCam/TACPRO-cd/HI7Y4988.jpg

(Nightforce 3.5-15x50mm NPR2 with multi-turn, 10MOA, 0.25MOA click knobs, on an AI-AWM rifle. Photo by Frankie Icenogle used with permission.)

Zero-stop

If an external knob has a "zero stop" feature, the knob will physically stop turning at or near
its "zero" setting. When the shooter wants to dial back down to his zero, he can turn it until
it stops.

A scope without a zero-stop, like the pictured Leupold, has a knob that will keep turning until
the erector assembly bottoms out in the scope body tube. Each revolution the knob turns move the
knob up or down, just like a jar lid. On a scope without a zero-stop, the shooter typically
notes which "hash mark" the zero-revolution corresponds to.

Single Turn, Two-Turn, and Multi-Turn Elevation Knobs

In many scopes, a larger click size means fewer revolutions of the elevation knob are required to
reach its maximum elevation. A good example of this is the Leupold M3 knob, which turns only one
revolution but has 1 MOA clicks. The opposite example would be the Leupold M1 knob, which has
3-5 revolutions depending on scope model and 1/4 MOA clicks.

apollo.demigod.org/~zak/DigiCam/TACPRO-cd/HI7Y4565.jpg

(Leupold MK4 M3 scope on a Remington 700. Photo by Frankie Icenogle used with permission.)

Some scopes are designed to have very many small clicks in only one revolution. A good example
of this would be the US Optics EREK knob, which has 90 clicks per revolution and can be ordered
with 0.25, 0.5, or 0.1MIL click values, which would yield 22.5MOA, 45MOA, or 9.0MIL travel per
revolution.

Likewise, some scopes are designed to have just two turns of travel, with some indication to the
user which revolution the knob is on. The best example is the Schmidt & Bender "Two Turn" PMII
scope, which has approximately 27 mils of travel in two revolutions. Even the two-turn scopes have
enough travel in the first revolution to shoot to 1000 yards with 308WIN.

apollo.demigod.org/~zak/DigiCam/TACPRO-cd/HI7Y4123.jpg

(Schmidt & Bender "Two Turn" PMII mounted on an AR10. Photo by Frankie Icenogle used with permission.)

A single or two-turn scope simplifies elevation adjustment by freeing the shooter from keeping
track of the current revolution of the knob. With a regular M1-style multi-turn knob, the
shooter consults his log-book and reads 17MOA, then has to adjust his scope up one full turn
(15MOA) and then two MOA past. With a single or two turn scope, he merely turns the knob about
1/3 of one revolution until the markings for 17MOA are visible.

Bullet Drop Compensators (BDC)

Some scopes come with bullet-drop compensator (BDC) knobs. These knobs are calibrated for a
certain load by having markings typically every 100 yards or meters on the knob itself, so the
shooter can look for the distance on the knob instead of the angular elevation amount. If the
shooter is engaging a target between marked distances, for example 450 yards, he will have to
guess or look up in his data which click value between the 400 and 500 yard markings to use.

A BDC knob is nothing more than a regular knob with markings that correspond to the load used.

Tube Diameter and Mechanical Limit of Elevation Travel

When the elevation knob is adjusted, it physically moves an assembly -- some lenses and the
reticle -- inside the main tube body of the scope, just "under" the elevation knobs. This
assembly is called the "erector" assembly because it inverts ("erects") the image coming from the
objective lens. The erector assembly travels up and down as the elevation knob is turned, and
left to right as the windage knob is turned. The movement of the erector assembly moves the
"zero" of the reticle.

The erector's movement within the scope body is limited by the side of the main tube diameter of
the scope. Thus the larger the scope tube diameter, the more elevation travel will be
mechanically possible. (It is also possible that the elevation knob mechanism itself limits
travel before the mechanical limit of the erector. This is most common in "one turn" scopes like
the Leupold M3.)

Scope tube diameters include: 1" (25.4mm), 30mm, 34mm (Schmidt & Bender), 35mm (US Optics), and
40mm. The advantages of the larger tube diameters are more elevation travel available and a
stronger scope. The disadvantage of larger tube diameters is that the selection of scope rings
is few, however, there are several high-quality ring sets available for 34 and 35mm tubes.

apollo.demigod.org/~zak/DigiCam/AI-AWP/small/164_6487_img.jpg

(US Optics 3.2-17x44mm SN-3 with 35mm tube has approx 18 mils total elevation in two turns,
ninety 0.1-mil clicks per revolution. Rifle is an AI-AWP.)

Reticle Features

The second method for elevation specification is to use reticle features. Many reticle designs
have hash marks or dots down from the main cross hair which can be used for hold-over. In a FFP
scope, the angles demarcated will be the same at any scope magnification. In a SFP scope, the
angles demarcated will change as the scope magnification is changed. Thus, without overly
complex calculations, reticle-based holdover is most useful in a FFP scope.

Just like the "click" sizes, the spacing of the hash marks for reticle holdover in part determine
the smallest engage-able target size. For example, if a reticle has 1 MIL demarcations (ie, in a
mildot reticle) and you need to shoot a 10" square target at 600 yards, you need to hold
approximately 3.4 mils high, so you'd put the target approx 40% of the way from the 3rd to the
4th mark. If the target is small, there is no precise sight picture-- you're holding "in space"
again.

A more sophisticated reticle designed specifically for reticle-based holdover (and windage) is
the Horus.

apollo.demigod.org/~zak/DigiCam/AI-AWP/small/164_6484_img.jpg

(View through Horus H25 reticle at approx 12x magnification, targets at 100 yards)

The Horus H25 reticle is mil-based, with small tick marks ever 0.2mil. A 308 shooter with the
H25 reticle can shoot to 1000 yards using the reticle only.

For example, at the TACPRO 2005 sniper match, there was a stage in which 5 targets had to be
ranged and engaged with one shot each under a strict time limit. I ranged the targets with my
laser and wrote their distances on my note-pad. As I moved from target to target, I only needed
to look up the drop for that distance and use hold-over in the Horus H25 reticle. I didn't have
to fiddle with any knobs. This demonstrates the speed advantage of reticle-based holdover. A
shooter should try to memorize his drop values, and it also helps if he can remember the current target
distances or have a spotter to communicate them.

apollo.demigod.org/~zak/DigiCam/TACPRO-cd/HI7Y5070.jpg

(Engaging multiple targets with the Horus reticle at TACPRO 2005. Photo by Frankie Icenogle used with permission.)

Hybrid Knob & Reticle

The last method for elevation specification is a hybrid, where the shooter might dial to an
intermediate zero like 500 yards from his primary 100 yard zero, and then use reticle-based
hold-under and hold-over for targets closer and further than the intermediate zero distance.

Reticle and hybrid holdover has the advantage of being much faster than dialing elevation changes
between shots at targets of different range. The downside is that sight picture precision is
reduced because of the larger granularity of reticle features vs. typical knob click values.

Again at the 2005 TACPRO sniper match, on a stage where I knew the distances beforehand (325,
375, 500), I dialed to 375, and noted the hold-under for 325 (0.4mil), and the holdover
(1.1mil). While shooting the stage, I merely used the appropriate hold-under/over points in the
reticle.


First Focal Plane vs Second Focal Plane

In variable power scopes, a first-focal plane (FFP) reticle configuration means that the angular
measure of the reticle features stays constant. No matter what magnification it is set at, 1 MOA
will be 1 MOA and 1 MIL will demarcate 1 MIL.

The FFP comes into play because with a wide range variable scope (my SN3 is 3.2-17x), dialing
down the power will widen the field of view. Target to target transition times are drastically
improved by widening the field of view. The ability to locate targets is enhanced by a wider
field of view. To use reticle based holdover without the need to adjust to a specific
magnification setting, the scope must have a FFP reticle.

Another advantage of the FFP is that ranging and miss-spotting can be done at any power and yield
direct accurate results.

Exit pupil size numbers increase as the scope magnification is dialed down. That's the math
behind the observation that a scope at a lower power will produce a brighter image than the same
scope dialed up in power. During the day it doesn't make a difference. During the night, it makes
a big difference in target ID and sight picture. For an illuminated reticle to be useful, its
features need to demarcate the same at whatever magnification is needed for low light.

A FFP reticle setup allows reticle-based and hybrid reticle/click holdover to be used at any
magnification setting.

There are some disadvantages to a FFP reticle in certain situations. As the magnification
is increased, the width of the lines which comprise the reticle increase in apparent size and
will obscure more of the target than the fine lines in a SFP reticle. Conversely, when the
magnification is set near the bottom, for example at 4x on a 3.2-17x optic, the reticle lines
"shrink" in size along with the target image and may become difficult or impossible to see in
some lighting conditions due to their very fine width.


Windage specification

Windage works just the same as elevation. Knob clicks or reticle features can be used. The big
difference is that the amount of wind hold off is much less than the maximum elevation required
for the cartridge's maximum range. A typical 308 load might have 8 MOA deflection with a 20mph
cross-wind at 800 yards, while it needs about 18 MOA of elevation at that distance. This means that
windage travel is typically not an issue.

Because wind changes can be very dynamic, using the reticle for windage hold-off can be more
effective than dialing wind. For example, by the time you notice the wind and dial a correction,
it may have changed already. Using reticle windage hold-off can be immediate.

Lead specification

Again, lead works basically the same as windage.

MIL vs. MOA

In principle, either system can be used. If you're thinking about or communicating elevation
values (for example looking at data and then dialing or holding off), a typical elevation value in
MOA for 308 looks like "11.25" which is four digits, but the same mil-based would be just "3.2" or
two digits. (In fact you can go out to over 1000 yards before needing more than two digits of
elevation in mils.) This is less information to process.

Parallax Adjustment

There are two types of parallax adjustment. The first is an adjustable objective, in which the
objective bell itself rotates to adjust parallax. The second is a rotating knob typically on the
left side of the scope, opposite the windage knob.

The adjustable objective is optically simpler, meaning fewer lenses and more clarity and
brightness, but the shooter must reach forward to the objective to adjust it. The rotating knob
adjustment is more convenient since it's located closer, near the rest of the turrets, however,
more lenses are involved which can reduce clarity and brightness.

In either case, some parallax adjustment knobs or objectives are marked for range so the shooter
can dial it based on the target distance. Others are not marked with distances, and it's up to
the shooter to determine visually when the image is in focus and parallax-free.

To determine if parallax exists at a certain distance, the shooter aims at an object at that
distance, then moves his head slightly side to side and up and down without moving the rifle. If
the reticle aiming point stays "on" the object, then it is parallax-free. If the reticle aiming
point moves with regard to the object, then some parallax error is present.

Reticle Illumination

In some low-light conditions, it is difficult or impossible to see a black reticle on a dark
target. Most tactical scopes are available with the option of an illuminated reticle.
Mechanically, this consists of some type of external switch or brightness adjustment control, a
battery, and a light source such as an LED (light emitting diode) inside the scope actually
providing the light to the reticle.

Some reticles are fully illuminated, but some reticles only illuminate their center portion. A
fully lit reticle can be too "busy" visually, while a partially or center lit reticle might not
illuminate all the reticle features. Brightness adjustment is critical. If the reticle is
too dim, it might as well not be illuminated at all. If the reticle is too bright, it will wash
out and obscure the target.

There are several methods to turn on or adjust the brightness. Leupold scopes have an
on/off/brightness turret at the 10:30'o'clock position on the ocular housing, just to the rear of
the power adjustment ring. This is offset from the elevation adjustment knob, but still obscures
it somewhat. Nightforce scopes have a simple on/off switch activated by pulling put the cap of
the parallax adjustment knob. Schmidt & Bender have an auxiliary knob on the side for on/off and
brightness adjustment. US Optics scopes with illumination similarly have a auxiliary knob
somewhere on the turret housing of the scope, location depending on other scope features.

Illuminated reticles, when turned on, are visible from the front of the weapon, through the
objective lens as a red/orange light. The frontal visibility depends on the angle of
observation, the intensity of the reticle, and scope design. If it is critical to not be
observed from the target area, then reticle illumination must not be used.

apollo.demigod.org/~zak/DigiCam/TACPRO-2005/small/165_6559_img.jpg

(During a night shoot, shooters are visible only by their cylume chamber flags.)

Brightness, Magnification, and Objective Size

Most modern tactical scopes will have similar image brightness during the day, but differences at
twilight and low or no-light can be dramatic. There are three main factors which affect low-light
brightness: lens quality, magnification, and objective lens diameter.

The easiest way to increase brightness is to dial down the magnification on adjustable scopes.
There is an inverse relationship between magnification and image brightness. This is another good
reason to choose an adjustable magnification scope.

The second two factors affecting brightness are characteristics of the scope itself. Given two
scopes with the same lens quality, the one with the larger objective lens will be brighter simply
because it can focus more incoming light from the target area through the scope's lenses.
Finally, lens and lens coating quality is critical to image brightness. Higher quality lenses and
coatings will pass through more light and less brightness will be lost through the scope itself.

There is a trade-off to be made between objective size and mechanical considerations. A scope
with a 80mm objective will gather 4x more light than a 40mm objective, but it will be much heavier
and will require extremely high mounts to clear the objective bell over the barrel. Mechanical
considerations favor the smaller objective, and a lower sight over bore distance is preferable
since it reduces the mechanical offset.

apollo.demigod.org/~zak/DigiCam/TACPRO-cd/HI7Y4418.jpg

(A US Optics SN-3 with a 58mm objective lens. Photo by Frankie Icenogle used with permission.)

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CONCLUSIONS

The following is the end-point I've arrived at after going through all of the above. A practical
long-range rifle shooter who wants to shoot MOR, sniper, tactical, and field matches should pick a
scope with the following features:

1. Variable magnification in the 3-18x range. Low power is useful in low light, on close targets,
and on movers. Higher magnification helps for target ID and sight picture at long range. Scope
must have parallax and focus adjustment.

2. Knob "clicks" no more coarse than 0.5 MOA. The standard clicks of 0.25 MOA or 0.1 MIL are great.
0.1MIL is about 1/3 MOA. Clicks in this range are fine enough to allow precise specification of
elevation for small targets.

3. The elevation knob should have a zero-stop set up to allow either no clicks below "0" or up to a
couple MOA "below" 0. The zero stop helps to prevent the shooter from being a full knob-turn
revolution off from where he intends to be, and is easier to check settings in low light
conditions.

4. The reticle must be of a first focal plane configuration. The FFP reticle allows use of reticle
features at any magnification setting, which is useful for target location, tracking of moving
targets, fast engagements, spotting, and low-light.

5. The reticle should have angular features in units useful for both hold-over/under and windage
hold-off. Typical units would be 1/2 MOA hash marks, or 0.2 or 0.5 MIL hash marks. The Horus H25
reticle appears busy, but is ideal for rapid engagements of multiple targets at different
distances.

6. The angular units of the reticle features must match the angular units of the knobs' "click"
values. There is no reason to have two different "systems" in use on the same scope. If the
clicks are in MOA, the reticle features should be in MOA. If the reticle is in mils (e.g. Horus
or Mil-dot), the knob clicks should be in mil units.

7. Field-adjustable illuminated reticle. The illuminated reticle dramatically improves sight
picture in some low light environments. The ability to adjust the brightness in the field is
critical to prevent wash-out with a super bright reticle setting. The downside of an illuminated
reticle is that it can indicate the presence of the shooter.

8. Objective size. A good compromise point is a 44-50mm objective provided that the scope has very
high quality lenses, such as those from Schmidt & Bender or US Optics. A larger objective size in
a scope with lower quality lenses may be less bright than a smaller objective with high quality
lenses.

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A Note About Cost

Many people balk at spending $1000 or more on optics. This is misguided. High quality optics are
one of the best places to spend money in a precision rifle system. Along with the rifle
action, stock, and mounts, these costs are fixed over the life of the rifle. The cost of training,
ammunition, and barrels dramatically eclipses those fixed costs.

To illustrate the point, let's analyze the cost of training with a high-end factory precision rifle
(AI-AE) using a top of the line S&B or US Optics scope for 5 years. A rifleman with a moderate but
regular training schedule might shoot 3000 per year. If he is shooting 308, a realistic barrel life
might be 5000 rounds until the groups increase beyond his spec. Over the 5 years, that will be
15,000 rounds and 3 barrels. For ammunition cost, we will use a conservative cost from what
reloaded ammunition might cost.

Rifle cost         $2500 (AI-AE minus the first barrel)
Scope cost         $2100
FIXED COSTS -----> $4600

3 barrels          $1800
15,000 reloads     $6000
CONSUMABLE COST -> $7800

This comparison doesn't even include the cost of formal training, match fees and travel costs. If
you plan on shooting regularly to achieve a superior level of proficiency, it makes sense
to buy the best rifle and scope you possibly can.

#############################################################################################################

Picks

Based on the above list, there are basically three choices that meet all of them:

1. US Optics SN-3 3.2-17mm

2. Schmidt & Bender PMII

3. (Caveat) Leupold Mark 4 "FF". The M1 version of this scope has no zero stop. The M3 version of
this scope has a zero stop, but coarse 1 MOA clicks.


Good Shooting & Stay Safe.

apollo.demigod.org/~zak/DigiCam/PNCLS-2005.08.06/small/169_6905_img.jpg

$Author: zak $
$Date: 2005/12/30 20:25:20 $
$Revision: 1.22 $

Originally Posted By Lawman734: Zak, thats an outstanding read and hope everyone else here takes the time to read it other than just looking at the cool pictures. This really needs to be tacked at the top.

+1

Damn, pretty much everything you'd want to know. At work so this is a taggity for later. Thanks for the info.

Tag - +1 on the tack

Pretty damn decent but I didn't see any mention of scopes that make use of a ballistic cam like the Leupold M3 series, could be somewhat useful to do a comparison between the two comparing the trades offs between speed and precision.


Also, some out there argue about the merits of a side focus parallax adjustment while others find them a bit lacking or even problematic in some instances(Leupold Long Range specifically).

excelent post. this needs a tack. thanks. i'll be checking back soon.

Originally Posted By uglygun: Perfect. You and I frequent some of the same forums and I know we've read some of the same debates on this stuff.

I'm jonesin' for more info and discussion. Could you list some good forums on precision rifles?

tag & another +1 on the tack. thanks for the info Zak.

Valid arguments for sure.

It's part of the reason I stick with 1/4 MOA adjustments because I primarily try to hit little furry buggers at distances farther than something like an M3 cam might permit me to dial into.

But if you are banging steel silouettes out to maybe 600 yards and a bit beyond on a budget the M3 might work out nicely. I'd love an S&B scope but like the USO(would love one with the EREK knob) scopes they are similarly out of my price range.

Having one or two Nightforce 5.5-22x scopes in my collection and the remainder being Leupolds is about all that I can foresee.


Due to price constraints, my preferred optic is a Leupold 6.5-20x M1 preferably converted out to a Premier Reticles Gen 2 XR mildot reticle on the front focal plane(or Gen 2 at the very least). Sure the scope is starting to get expensive by the time the work is done to it but a used 6.5-20x LR can be had for a decent price, maybe 600-650 bucks, the reticle change should be around 240 from Premier Reticles, and an M1 knob install should run between 75-120 bucks depending on if it had target knobs or not.

Would love the quality of a S&B or USO but 1700-2200 for a scope is way out of my price range, 1200 bucks is about tops.

Zak, very nice write up.

Another BTT till a mod tacks this. Really good info Zak.

Originally Posted By Pthfndr: Another BTT till a mod tacks this. Really good info Zak.

If he's gonna do a second draft to this, that should be tacked. This is good stuff but it sounds like he's got more brewing in his noggin'.

Originally Posted By uglygun: But then there's always the ability to learn hold overs in mils like you talked about earlier in your post. Part of the reason I want the Gen 2 XR is for the 1/2 mil hold overs as well as the nearly "Horus-like" reticle.

UG, make sure the XR is what you want instead of the original Gen II because the XR has smaller dots and might make ranging or holds harder in lower light. If they made it with the standard .2 mil dots then I would have gotten it but it's dots are too samll for me at about .1 mil depending on the scope you get it in. I do love the Gen II though. I use it for all my windholds as I never touch my windage after zeroing.

I agree that the M3 series isn't meant for varmint hunting unless it's the 2 legged kind and there it shines over the M1. Yes there are the load drawbacks and coarser adjustments but if you know your equipment, as you should, they are all able to be worked with. The load can be worked with or the dials remarked as such

Or if you weren't cheap, like me, you can get the Kenton knobs. You will never be off more than 1/2 MOA at any range and that's just 5.25" at 1000 and as I said if you know your equipment that's just a small hold. Even smaller MOA sized targets at 100 and 200 can be hit reliably.

Also one turn to 1000 is a good thing in competitions. Just ask anyone who had an M1 and had been off a turn ;) Happened a few times to shooters at this years ASC. It all boils down to the use of the scope.