MSR-reticle development and features
MSR-reticle development and featuresFinnAccuracy MSR-system reticle is currently licensed to following scopes and manufacturers: S&B PMII 5-25x56, 3-20x50 Ultra Short and 5-20x50 UltraShort.Steiner Military 5-25x56 and 3-15x50.Kahles K624i 6-24x56. MSR Scopes you will find here.
To exploit full potential and all features of MSR, user must be familiar with milliradian system and fully understand few related formulas. Some parts also require memorized rules- very simple ones but still. MSR was never intended to be novices reticle, for benchrest, or to be optimal for occasional Sunday paper punching- but basic layout and principle is still easy enough for beginners- offering more and more possibilities down the road as experience and skills accumulate.
In a nutshell - MSR is divided to three main parts: main reticle, fine milling scale and rapid ranging scale. Layout was done accordingly to principle that top part of reticle will be kept clean. To keep overall look as simple as possible while maintaining defined versatility, main reticle has 4 basic functions: shooting trough whole magnification range, measuring TGT size, rapid milling with illuminated center cross, and to be used as large mil-scale covering entire FOV.
Center cross dimensions are 1x1mrad. Besides being even and sensible 0.5mrad hold-off/correction reference, it offers possibility to use dimensions as rapid scale based on simple memorization. (see lower attached image) Illumination improves visibility in many kind of situations, but mainly in dusk or dark. Center cross is only illuminated part of MSR. According to our experience, illuminated surface area of any reticle should always be kept as small as possible. Even with dimmest intensity, illumination tends to interfere observing eye when amount of usable light in FOV is just in limit for recognizing objects in observed area. This is valid and potential problem with military grade clip-on night visions as well. Same principle naturally works with any 0.5/1mrad reference line. But as MSR center is separated from actual hair line with air-gap, it is somewhat simpler and faster to use. Also illumination highlights it, and ability to keep aiming point on top of target while estimating final range may be very valuable asset in certain situations.
Main hair line
Main hair line thickness is commonly debated issue. Most, if not all, agree that highest precision requires very thin line- but actual line weight is still more or less matter of personal preference. In another hand, purpose of reticle forces line weight into certain limits. Very thin line can not be used in all conditions and is far from optimal for everything- and is especially problematic with lowest magnification with current 5x or over magnification ratio scopes. Same naturally apply with very thick line too.
MSR line thickness was selected by impressing practicality: It is thick enough for use in dusk, daylight heavy mirage in hot environment and against dark background in daylight with lowest magnifications - but it is still thin enough for long range shooting. In low visibility and with low magnifications even thicker line would not hurt, but then high magnification and long range accuracy would start to suffer.
Standard 5-25 MSR hairline weight is 0.05mrad. As calculated example, 250mm / 10" wide head size target will be completely covered by line at 5000meters/3.1 miles and further distances. We find this sufficient for any practical field shooting.
Still - even with otherwise identical reticle design, line weight should and must be scaled to match scope magnification limits. For instance, Steiner Military 3-15 MSR reticle line weights are optimized and tad thicker than MSR on 5-25 scope. It still "looks and feels" exactly same for eye used to use MSR 5-25 version - because of changed thicknesses. Both vertical and horizontal hairline consist continuous 1mrad scale with 0.5mrad division marks. All 0.5mrad marks are 0.02mrad thinner than 1mrad marker lines - and are also shorter length than even 1mrad marks.
Using line+shape combination was considered very carefully. Using traditional line+dot combo would offer good natural "contrast". Dot shape would also feel cozy for people used to traditional mildot- me including.
Line was finally selected for couple of reasons. Any pattern will cover multiple times more area than line with same length. Traditional dot and precision are also somewhat difficult combination from precision principle point of view - it is very hard to pinpoint where exactly small curved shape edge begins and where it ends. So, after trying multiple shapes, simple line was chosen.
Sense of line thickness/length idea is easy to see in practice- even 1mrad marks clearly pop out, without careful looking and/or further thinking. Risk of mixing up lines in a hurry is therefore reduced significantly. Still, if 0.5mrad precision (or 0.25mrad by halving empty space) is needed, marks are very easy to find and use.
Hairline lower vertical part is extended for extreme long range shooting. For instance, 338 Lapua Magnum requires roughly 45mrads of elevation at 2000meter/1.25miles range. As even most of latest design scopes can not be adjusted for such a long ranges directly with turret, reticle reference with lower magnification has to be used at some point. MSR vertical line offers aiming reference scale for whole FOV, 27mrads in S&B 5-25 scope with 5x magnification.
Vertical line has also 0.5mrad division marks. Full 10mrad lines are both numbered and wider to minimize user errors and 5 mrad lines are wider for same reason. Horizontal main hairline ends to 0.2mrad division scale. Line weight is tad thinner than on main hairline, 0.03mrad, but thicker than ultra-fine "L" -scale with 0.02mrad thickness. Idea and purpose of scale is ability to measure with it visibility conditions where 0.02mrad is too thin. Mirage, low contrast target or dusk for instance.
As spotter/observer usage capability was one of the main design principles, separate "binocular style" markers were added. Numbered 10mrad marks are very useful if whole FOV with lowest magnification is used for large area observation or for target acquisition between sniper team. Pinpointing exact position fast from terrain lacking distinguishable reference points needs large reference scale. Same problem occurs when measuring long angular distances between points on visible area- this has always been blind spot with aiming scopes and even with many spotting scopes. Similar numbering/line width principle is also used in lower vertical hair line.
Marked dimensions on lower vertical hair line are also needed if reticle is used for hold-offs in extremely long shooting distances.
Fine inverted "L" was placed as close to center as possible without harming shooting usability in typical situations.
Best possible precision milling requires best possible optical quality. Resolution and usually best overall image quality is always located at center of FOV, regardless of scope manufacturer and type. Difference is bigger than most users realize.
5mrad tall and 5mrad wide "L" consists 0.1mrad hash marks in both ends of vertical and horizontal hair lines. If main hair line is used as base, any target size between 0 and 7 mrad can be measured directly. Free horizontal space to vertical main hairline is 1.5mrad.
If main hairline hashmarks are used for direct hold-over aiming with center cross zeroed to 100m, L scale vertical line ends at 900 meters aiming point level. If wind is compensated with hold-off too, aiming point will not intersect L-scale line if wind magnitude is less than fair 11mph or 5 meters per second direct side wind.
On right side of hairline, different quick ranging scale location allows bit more wind before intersecting with aiming point- 6 meters per second / 13.5mph at 750m hold-over range.
Naturally target can be aimed with additional scale on top of it, but this disturbs impact observing.
Example calculated with 338 Lapua, 250gr with typical factory load velocity and summer atmospheric conditions.
400-1300 meters rapid ranging
None of previously mentioned features offer rapid "fail-safe" milling without any calculations or memorization. Various pre-calculated "stadiometers" have been used in many military scopes over decades - for a good reason. It is very simple and fast way to get reasonably good idea of target distance.
So, principle is old, but MSR is with some tweaks. Unlike any other system we are aware of, MSR ranging system is unique with two layers and shared baseline. Two-layer design saves room and cleans up reticle overall look without sacrificing accuracy.
Narrower width also offers possibility to keep scale closer to optical center. Location is important both to achieve best optical quality - and to keep it completely visible in largest magnifications where FOV is very small. Also, close proximity from center keeps aiming point shift/movement from milling back to center of the reticle as short as possible.
Line dimensions are based on average height and width of human. Each line width corresponds 500mm/19.7" shoulder width at numbered range. Number means hundreds of meters.
Reference height for is 1meter/39.4" tall object. Dimension equals average height between groin and top of head.
Having both horizontal and vertical references is useful, as target may be sideways or in angle. Picturing groin location is possible even if not directly visible - and using longer reference dimension reduces error in final ranging result if absolute milling accuracy is kept same.
Same reference lines can also be used for half or double sized targets by multiplying or dividing ranges by 2. if actual width is 10" instead of 20" (19.7") and reference line matches, marked range should be divided by two for corrected distance. If actual target size is double, true range is double as well.
Traditionally this type of ranging scales use man height as vertical reference. Reference is bit problematic as vegetation, terrain shape or snow often hide legs. Also in certain environmental conditions may bend/shrink image and cause error in measured height. Phenomenon is called refraction, and it is usually strongest very close to ground where hot and cold air meets. This is rarely actual problem if not in desert, but still one small thing effecting selected dimensions.