Ok folks.  Here's revision 1.15.

Also available directly here: demigod.org/optics

OPTICS FOR PRACTICAL LONG RANGE RIFLE SHOOTING

(C) Copyright 2005 Zak Smith All Rights Reserved

Reproduction or Republication by express written permission only



(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.

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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.



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, ending around 11.5" low at 300
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.



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.

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



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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.  



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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.



(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 40 MOA 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.



(Nightforce 3.5-15x50mm NPR2 with multi-turn, 10MOA, 0.25MOA click knobs, on an AI-AWM rifle.)

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.



(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.



(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.



(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.    



(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.



(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.



(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.



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

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



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.

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

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
RECURRING COSTS -> $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.

$Author: zak $
$Date: 2005/09/01 00:26:30 $
$Revision: 1.15 $

Well I would add some things to make it complete.

For instance discuss the objective size vs. magnification vs. usability in low light and make a reccomendation of objective size vs. bulk weight considerations etc.

Discuss tube diameter vs internal travel of adjustments and the difficulties with finding 35mm rings etc. if you go very large.

Discuss illumination systems more.  The US optics has full illumination but batteries die in under 12 hours at max.  S&B just has a little + illuminated on the scope you reccomend instead of full illumination of the mildots, etc.  Id discuss brighter reticles like the flash dot on the S&B (not offererd on th larger scope?) being used to get an object centered in your scope faster by using a BAC style aiming so you dont have to hunt for your target at 16X. Position of ht e illumination dial and how some block the elevation turret (top, 45 deg, side mounted, integral with focus knob etc)

Discuss objective parrallax focus vs side focus and the simplicity of the objective focus vs convenience of the side focus, some are marked for focus at ranges some are not etc.


PS: You should put the prices on the scopes you reccomended so people wont fall over when they realise they are almost $3000 lol.

tag for when I have time to read.

Quoted: Well I would add some things to make it complete.

Good ideas. I'll put those on my todo list.

tag for morning

TAG!

Two Cents...
I would disagree with the premises that 1moa adjustment is too coarse. I appreciate the 1 moa adjustments as they are...
1. fast and
2. Idiot-proof.
Two attributes that I appreciated and was able to put to good use during several long range rifle classes.
Case for point 1, I have seen a number of shooters lose track and be a full turn off, typically 15 minutes high. Since my M3 can only go around once, if you look, you should never have this problem.
Case for point 2, during the shoot off at Gusite TR-1 another shooter and I were both adjusted for targets at 220 yards, the instructor (Alan Heckert) called for us to shoot, what would be, the last target at 750. Since I had to adjust less than a full turn I was on target first, thankfully I didn't yank the shoot and spoil the advantage I had...that time.

Nit picking, sure but you asked.
out

Both are arguments for a many-click, zero-stop elevation knob such as the USO EREK or the SB Two Turn, not 1 MOA clicks.

I would disagree with the premises that 1moa adjustment is too coarse

Depends on target size and distance.    A 4" plate at 550 yards will be hard to hit with 1 MOA elevation clicks.    In fact, there's a 30% chance that one click setting would be low and the next would be over the top.   (I made that shot two weekends ago.)

With a larger 10" plate at 800 yards, you get 1.7" of margin with 1 MOA clicks.

Superb condensation of information that has taken me a long time to amass.  The information is out there, just not in one place.  I would add that as a long distance static shooter (prairie dogs and hunting) I opted for the finer cross hairs of the 2nd FP scope and ended up with a Nightforce.  I sort of understood what I was sacrificing, but after reading your article it is much clearer what I am giving up.  

Great job, and I hope that you can work something out here that might allow it to be archived or tacked.  Might be nice to get paid for it, though.

One thing that I might mention if your intended audience might include those other than persons making these decisions for a living, might be to mention actual shooting for confirmation of data.
Also, perhaps a mention that a 30mm tube typically has more reticle adjustment than a 1" tube.

Might be helpful to everyone here in making comments to understand if this article was written as general information helping anyone make decisions, or whether it was written, aimed at the working professional, to help narrow down the choices (or perhaps justify to the boss the expendature ).  It appears to be the latter.

excellent work,

Craig

Yep, for benchrest or static targets, the SFP NPR2 is great.

I do have it presented on a web-page too, so to not depend on the thread.

I have added some about scope tube sizes to the next version.  Your idea about shooting confirmation is a good one to add also.

As for its purpose, it's aimed at anyone who wants to do "practical long range shooting", as defined, effectively, professional or recreational.  

-z

Quoted: Two Cents... I would disagree with the premises that 1moa adjustment is too coarse. I appreciate the 1 moa adjustments as they are... 1. fast and 2. Idiot-proof. Two attributes that I appreciated and was able to put to good use during several long range rifle classes. Case for point 1, I have seen a number of shooters lose track and be a full turn off, typically 15 minutes high. Since my M3 can only go around once, if you look, you should never have this problem. Case for point 2, during the shoot off at Gusite TR-1 another shooter and I were both adjusted for targets at 220 yards, the instructor (Alan Heckert) called for us to shoot, what would be, the last target at 750. Since I had to adjust less than a full turn I was on target first, thankfully I didn't yank the shoot and spoil the advantage I had...that time. Nit picking, sure but you asked. out

If I remember correctly the S&B Zak reccomends has a little window with yellow or something to let you know if its on its first or second revolution in elevation.  You say if you look you are not off on a 1MOA M3 scope but the same is true with the PMII as well.  So still no need for 1 MOA elevation.  Let me figure out what the hell I am talking about and I will get back.

OK I am back and here it is.

Unique to the PM II/LP is a color-coded elevation knob that gives the shooter instant reference to where the elevation is set. Just one turn of the knob provides 28 minutes of elevation. A window within the dial then changes to yellow, and one additional turn provides an additional 28 minutes of adjustment. Thus, the complete 56-minute adjustment range can be covered in only two turns of the elevation knob, while the dial’s window graphically shows the shooter where they are within the overall range. This solves the problem posed by many tactical scopes when the shooter can become “lost” within an adjustment range requiring several turns of the elevation knob, especially under stressful conditions.

Excellent write up!

Tagged for updates.

Along the lines of what DevL was saying about the SB knob, the USO EREK gives you 9 MILs in 0.1mil clicks or 45 MOA of elevation in 1/2 MOA clicks, in one turn, which is enough for 308 past 1000.  And it has a mechanical zero-stop.   Don't assume that the 1 MOA M3 knob is the only alternative.

ETA:  My ITRC shooting partner's bolt rifle has an older S&B PMII scope-- it's in the first picture in the first post.  It has 13 MILs of elevation in 0.1mil clicks, only 1 turn, with zero stop.

Holy $hit Zak.........when, where and how do you come up with this info?

Cut and pasted your entire post into a word doc so I can read it at work.  Too much good stuff to glance over it.

Zak,
Great post, the kind that we seem to be in short supply these days.  Excellent photos too.

Side question, how do you like that Horus?  I like the concept, but it almost seems too 'busy'.  What are your impressions?

Thanks again!
Forest

Quoted: when, where and how do you come up with this info?

You just have to notice what you're trying to do, and figure out what you need (and need to do) to do it.

Forest,

Side question, how do you like that Horus? I like the concept, but it almost seems too 'busy'. What are your impressions?

It does look busy, but I got used to it after a few days.  Like I said in the article, I love it for fast engagements,  but remember it's not a benchrest reticle.  It's for practical targets.

fantastic thread, tag

Tag for later dont have time to read it all now

Latest revision edited into top post.

Tag for tomorrow at work when I'll have time to read

tag

You know there is an "articles" section of arfcom. Informative posts, like this one, should be archived there with the author's permission, of course.

tag like a mother freaker.  You rule!  looks great.  I'm in class though.  And it's actually interesting!

Very nice Zak.

Tag.

what no unertl???????????????????????????????????????????????

Quoted: what no unertl???????????????????????????????????????????????

The Unertl is fixed 10x.
I can't find the specs, but it looks like it has a mildot reticle and MOA-based clicks.
No idea about the travel, but it will be limited by the 1" tube.

tag for time

What i read looks great though

Tag.