Posted: 10/27/2014 11:17:05 AM EDT
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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.)
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:
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.
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.) ############################################################################################################# 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.
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
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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). |
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The M3 is merely a 1-turn 1MOA-click knob, but has distances written on it to correspond to the intended load. It's not really a cam (which would sort of imply the same number of "clicks" per 100 yards/meters, but increasing elevation travel per click). But that's a good point. I'll add something about labelled knobs, size of click vs. speed, number of turns vs. speed/simplicity, etc. I have added something about the parallax adjustment types in the working copy. Keep the suggestions coming. I'll post an update here when I replace the top post with the newest version. ( I have about half the suggestions already added, but I don't think my match schedule will let me finish for a few weeks.) |
In complete agreement on those points on just how an M3 behaves. But newbie minded folks to the precision shooting realm may not know the assets or merits of one version as opposed to the other version. Will something like the M3 allow enough precision for the person who's primarily a target shooter or varmint shooter? Or will they require the speed and relative certainty of the M3 type cam allowing them to quickly dial into distance and being 1/2MOA high or low isn't going to be that critical.
Perfect. You and I frequent some of the same forums and I know we've read some of the same debates on this stuff. Still wish I had the money to have bought the Nightforce 5.5-22x off you but I'm still broke. I also don't fancy still having to have my remaining Leupolds converted to FFP Gen 2 XRs. |
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There are some decent discussions that go on over at www.snipershide.com Just browse back a few months though before going post crazy, some things have been covered quite a bit. It's also a good place to stop off if you are in the market for a used scope, there have been a number of decently priced Leupold M1 type scopes with and without mildot reticles being sold in their equipment exchange(6.5-20x and 8.5-25x varieties for 650-800 bucks respectively in some cases). USO also had a group by of sorts on some of their scopes, Zak has a nice little gem he got out of that deal. Was out of my ballpark when it was going on though. |
M3 is too coarse for distance work on anything but full man sized objects. At 300 yards and beyond you can easily be off target on a small animal even though you are one the correct tick. The S&B PMII reccomended in the thred has 1/4 MOA adjustments 2 turns to lock with zero stop and a window to tell you if your on the first revolution or second. Much better idea than the M3. I did not enjoy the lack of accuracy the M3 produced at long range. |
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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. |
Silhouettes at 600 yards are not...
Also note that that S&B Two-Turn scope comes in both a MOA version AND a MIL version. I believe the MIL version actually has more travel in the same number of clicks because 0.1mil is approx 38% larger than 0.25 MOA. -z |
Only reason I brought up the M3s was because of this last part of that quote. I suppose I was looking more at the constraints of speed. Sorry I glossed over or missed the part about playing around at the tail end of the super sonic flight range.
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. I suppose in your write up about the M3 series it would be a good idea to mention why they can have their drawbacks such as chasing a load that matches the provided dials otherwise having to make up your own dial for your specific load. |
Yep, and that's a great reason to get it converted to FFP. -z |
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. |
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I want the Gen 2 XR because one is going on a 50BMG for certain and the other is going on my 300WinMag which also has a big rebuild planned for it(wanting 210-220grns at 2900fps). For the kind of range those things are capable of I'd prefer to be able to have access to some smaller mil graduations to help with ranging. My mil-dot master may only go down to .3 mils but my pencil and calculator can do whatever if I have to resort to doing it by that means. The additional mils on the bottom vertical reticle is what really attracts me as well as some of the horizontal holds which could help a spotter make calls to adjust for windage and elevation holds. I have two 4.5-14x LR models and two 6.5-20x LR models that are gonna get converted. Gonna try to pick off an 8.5-25x LR if I can find one for a decent deal as well. I've already called Premier about the reticles back in May, was told then they were still waiting on the things to be delivered. Then recently I read that the reticles they took delivery of were not to their satisfaction so now they are again waiting for delivery of reticles before they can install them. |
I could see it on the 50BMG but just having smaller dots doens't seem like it would make it easier to range for me. I feel the .2 mil dots are about perfect as they can be broken to .1 if touching the bottom or top. Also mil hold corrections are easy with the Gen II. But that's the fun in this sport, if you want it then you get it. Let us know how it works out for you.  The 300WM with the 210-220s are a good plan but I would say stay with the 210 VLDs. I have made that my go to bullet now with a load of RL22 and it gives me about 2930fps out of a 26" barrel. I've used it out to 1500 yards and it hits. It has a better BC than the 220 SMKs and I found it fouls less also. I don't know if it's the jacket or what but I've fired 90 rounds without any accuracy decline. On a side note to touch back to above, I also ranged out to 1500 with my Gen II in a 6.5-20x50 Leupold that sits on the 300WM and it worked very well. I also used the 210VLD at this years Alleghany Sniper Challenge and came in second on my weekend, it was a two weekend event, and third overall for both weekends. Another note, the winner of my weekend was also shooting a 300WM with the 210 VLDs. The first weekend winner was shooting a 7mmWSM with 175SMKs just incase you were wondering.
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Zak, Thank you very much for offering such a complete volume of information on this topic. Long range shooting is something that has interested me for a long time, but I feel hendered to start in the subject due to the large volumes of information and misinformation out there. I have through the years found that myself that a FFP reticle only makes sense, and having a vari-power scope (not a fixed 10x) seems to be better. Also, to have an illuminated reticle makes sense as well. I would be very interested in hearing your thoughts on one other area of practical LR shooting. 1) Pro's and con's between gas system (semi-auto) sniper systems and bolt guns. Seeing that you switched your AR10 for a AI bolt gun. In my limited knowledge it would seem that an AR10's accuracy can match a bolt guns and having the semi-auto shots only seems logical. I also can't help but notice the new interest in a SASS by our government. Seems that it would have more firepower at more practical ranges. So is it just a matter of purpose between the two? Thanks for any information you can offer. Thanks, Jared, NE |
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Good info, but I kinda disagree that the only disadvantage of the FFP reticle is they get too big for precision work when on higher power. I think the greatest weakness of these is the fact that in low light up close (when you really need to dial down to low power for the wider FOV and larger exit pupil), these reticles tend to go away. And all illuminated reticles I've seen are visible from the front - bad. I know this write-up is geared toward competition, which I guess makes it a non-issue. I like SFP reticles that are more easily visible in the dark when I'm 50 yards and in (I can dial up to 10x for everything else, and I don't really need to mil anything at less than 100 - and really not under 200 in most cases). For what I do, I think the FFP reticles are bass ackwards - but again realize this was written with an eye toward competition. Overall, though, very good writeup. |
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SPDSNYPR, Good points about the FFP vs. low magnification, and frontal observability. I'll put those two points in my "to-do" list for this document. I have noticed that with illumination on, anybody within the target "region" can EASILY spot the red through the objective. Some of the FFP reticles have features that make them "work" on both high and low magnification. For example, the Horus H25 has thicker center reticle lines, and then much thicker side "bracket" line (kind of like a duplex). Can I ask- are you a LEO sharpshooter/sniper? jar3ds,
Maybe we could start another thread on an appropriate forum about the practical and doctrinal use of bolt-action vs. semi-auto sniper rifles. But for now, here are a few things to consider-- 1. the semi will be less accurate (eg- nobody shoots a semi for benchrest, but do you care about 0.75 vs 0.25 MOA?); 2. the semi will weigh more (same bbl length, etc); 3. the bolt will suppress better; 4. spotting hits will be harder through the semi due to reciprocating mass movement; 5. the semi will practically only handle 308-sized cartridges without ballooning in size and weight (eg, 300WM or 338LM); 6. the bolt will be more reliable. My own decision to switch from the 20" AR10 to the AI-AW was because the 20" seemed to run out of gas around 600 yards due to the velocity loss (and its effect on wind drift and drop rate), and spotting my own hits was difficult with the reciprocating mass chunking back and forth. The AI can do 1/4 MOA groups, while the AR10 would only do about 0.75MOA. You're right about "more firepower at practical ranges", in that you're referring to the current conflict where snipers are being used to clear paths of insurgents at relatively short distances. A reliable AR10 or SR25 is appropriate here. Just like every other question about weapon choices, it depends on what you want to do... -z |
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Quoted: SPDSNYPR, Good points about the FFP vs. low magnification, and frontal observability. I'll put those two points in my "to-do" list for this document. I have noticed that with illumination on, anybody within the target "region" can EASILY spot the red through the objective. Some of the FFP reticles have features that make them "work" on both high and low magnification. For example, the Horus H25 has thicker center reticle lines, and then much thicker side "bracket" line (kind of like a duplex). Can I ask- are you a LEO sharpshooter/sniper? Just resigned from the tac team a few months back, where I was the sniper team leader for 5 yrs. I am doing narcotics about 1/2 the time now, and still keep current w/ the long rifles (frankly, doing more entry work now - search warrants, etc.). I'm on a 5-man street crimes unit now and am covered up. Saw a Horus at a sniper school I went to about 2 yrs ago. I know what you're talking about with the thicker outer portion of the reticle, but when dialed down low, it still got awful small. If memory serves, I can't remember that it had a distinct, thick verticle line for finding the center in dark conditions - making finding the center of the reticle somewhat of a challenge. Of course, this is very limited exposure, and I have never used one in real life. I kinda found a scope I really liked in the IOR 2.5-10 and stuck with it. Like it better than our Leupold 3.5-10 LR M1's (on the issue rifles). The MP-8 reticle has huge outer reticle that is easy to pick up with little ambient light on low power. And I like the 1/2 MOA adjustments way better than the 1/4. It's just personal preference. If I woulda bought a Horus or Nightforce, I might like them better - but I don't have the money to switch scopes often (poor cop w/ a mean wife who doesn't like to let go of "our" money). I have put together a 22" bbl Rem 700 .308 with a lighter barrel (much handier). Am kinda shopping around for a scope (have everything else). Maybe I'll play with the FFP reticle scope if I can scratch the $$ together. |
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From what I've seen, LEO sniper shooting is much different than generalized long range shooting due to situational, engagement, and liability issues. The engagement distances are very short (average is 55-60 yards)and the targets are approx 1". This is somewhat of a different problem than arbitrary distance long range shooting. E.g. from 50 to 125 yards, typical 308 loads are within 1/3" under a 100 yard zero (ie, less than 1/2" error) and even a 10mph wind at 100 yards only produces about 2/3" deflection. In short, as long as you understand the mechanical sight/bore offset for very close (ie, under 40 yard) shots, you can just hold dead on. It's easy to figure out which sniper matches have a LEO focus-- you pound 100 yards targets all day. -z |
That kinda shooting is boring, you're right. Our training usually is. At least we throw some long range in there (our local range only goes out to 500, though) on stell-which is more fun. I don't do much sniper match shooting. Only real competitive shooting I do is highpower. And my highpower scope sucks .
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Zak: You put together an absolutely great compilation of scope information. Forgive me if you mentioned this, because I may have missed it trying to absorb all you wrote. One thing I find myself helping friends "de-bug" is a scope that for any of various reasons runs out of windage or elevation travel. Once diagnosed, I always stress to my shooting friends the importance of not only good glass, as there is no place where "you get what you pay for" applies any more than optics, but also mounts and rings. I cannot count how many times I have seen folks with freshly mounted scopes where, when initially zeroed, the knobs have been run out of adjustment, or cannot be zeroed because of a lack of movement remaining in the tube. Improperly aligned rings and mounts can destroy the value of a good scope. Geometrically, if the elevation knob is at its upper limit, the windage knob loses about 35% of its available travel( in a 1" tube), and will "bottom out" against the upper "side" of the tube. The same thing happens in any direction when one "starts out" with one of the adjustments too far from the center of the tube. Initial mounting should be shimmed, or machined, to allow for null positioning of the verticle and horizontal travel in order to retain as much "field" adjustment as possible. Just a random thought. And thanks again Zak. |
