Rifle Scopes Leupold CMR-W 5.56 reticle - ballistics reference variables ???

[dAyLiTe]

As many of you have guessed, I rather like these ballistic wind based reticles, as if you get them set up right, they are incredible.
...problem kicks in when you can't get them set up.

So I've been de-constructing the CMR-W and rebuilding it in excel, and I've got the structure sorted out... but the base data seems off ???

So here's what we know about the reticle: (from the published spec sheet)
5.56 NATO/.223 Remington
Calibre: 0.224
Weight: 62 gr
Muzzle Velocity: 2970 fps
Zero: 50 meters

and that:
0.86 Mil = 300m
1.82 Mil = 400m
2.98 Mil = 500m
4.41 Mil = 600m
6.14 Mil = 700m
8.23 Mil = 800m
10.77 Mil = 900m

... but it also says "For best results, the CMR-W reticle should be zeroed at 50 meters using 62 grain 5.56 NATO/.223 Remington ammunition producing a muzzle velocity of 2810 fps."
So is it 2970fps or 2810fps ???

I've also picked up articles that mention that the round used as a 62gr M855 FMJBT, which has a BC of G1.304 and is .907 inches in length.

So given all that data, I entered it all in JBM Ballistic Drift calculator, as the CMR-W has Spin Drift built in, using the following environmental variables:

Temperature: 25 c / 77f
Pressure: 29.77 in Hg
Humidity: 0%
Altitude: 0ft
Wind Speed: 0
Barrel Twist: 1:7 (more on this later)

I then get the following elevation feedback using MV:2810fps:
0.86 Mil = 223m (vs 300m)
1.82 Mil = 318m (vs 400m)
2.98 Mil = 411m (vs 500m)
4.41 Mil = 486m (vs 600m)
6.14 Mil = 596m (vs 700m)
8.23 Mil = 687m (vs 800m)
10.77 Mil = 779m (vs 900m)

and if I use MV:2970 fps

0.86 Mil = 243m (vs 300m)
1.82 Mil = 345m (vs 400m)
2.98 Mil = 444m (vs 500m)
4.41 Mil = 542m (vs 600m)
6.14 Mil = 638m (vs 700m)
8.23 Mil = 733m (vs 800m)
10.77 Mil = 828m (vs 900m)

...which is a hell of a big difference when I think I'm using the same input variables that Leupold are indicating they used to set up the CMR-W 5.56 in the first place.

So the things that could influence it are:
- The bullet used was not actually a M855 FMJBT
- My environmental variables are completely off.
- ???


In taking things a quite a bit further, I opened the CMR-W reticle PDF spec sheet in Adobe Illustrator and scaled the axes by the same amount until the vertical scale in Mils lined up with Millimeters in Illustrator. This then allowed me to read off the horizontal Mils to 0.01 decimal places to get the following table.

<table cellspacing="0" cellpadding="0"> <col width="64" span="9" /> <tr> <td width="70" align="center"><strong>WD-4</strong></td> <td width="70" align="center"><strong>WD-3</strong></td> <td width="70" align="center"><strong>WD-2</strong></td> <td width="70" align="center"><strong>WD-1</strong></td> <td width="70" align="center"><strong>Mil</strong></td> <td width="70" align="center"><strong>WD1</strong></td> <td width="70" align="center"><strong>WD2</strong></td> <td width="70" align="center"><strong>WD3</strong></td> <td width="70" align="center"><strong>WD4</strong></td> </tr> <tr> <td align="center">-2.391</td> <td align="center">-1.759</td> <td align="center">-1.115</td> <td align="center"></td> <td align="center"><strong>-1.818</strong></td> <td align="center">0.777</td> <td align="center">1.415</td> <td align="center">2.049</td> <td align="center">2.687</td> </tr> <tr> <td align="center">-3.182</td> <td align="center">-2.338</td> <td align="center">-1.499</td> <td align="center">-0.648</td> <td align="center"><strong>-2.977</strong></td> <td align="center">1.034</td> <td align="center">1.878</td> <td align="center">2.733</td> <td align="center">3.579</td> </tr> <tr> <td align="center">-4.068</td> <td align="center">-2.983</td> <td align="center">-1.905</td> <td align="center">-0.822</td> <td align="center"><strong>-4.415</strong></td> <td align="center">1.33</td> <td align="center">2.418</td> <td align="center">3.509</td> <td align="center">4.573</td> </tr> <tr> <td align="center">-5.014</td> <td align="center">-3.676</td> <td align="center">-2.334</td> <td align="center">-1.005</td> <td align="center"><strong>-6.149</strong></td> <td align="center">1.683</td> <td align="center">3.02</td> <td align="center">4.376</td> <td align="center">5.7</td> </tr> <tr> <td align="center">-6.055</td> <td align="center">-4.429</td> <td align="center">-2.814</td> <td align="center">-1.1188</td> <td align="center"><strong>-8.245</strong></td> <td align="center">2.049</td> <td align="center">3.669</td> <td align="center">5.291</td> <td align="center">6.907</td> </tr> <tr> <td align="center">-7.105</td> <td align="center">-5.2</td> <td align="center">-3.294</td> <td align="center">-1.375</td> <td align="center"><strong>-10.767</strong></td> <td align="center">2.45</td> <td align="center">4.366</td> <td align="center">6.275</td> <td align="center">8.196</td> </tr> </table>

Which reading between the lines indicates a Reticle Spin Drift of:
1.82 Mil = 0.148
2.98 Mil = 0.1985
4.41 Mil = 0.2525
6.14 Mil = 0.343
8.23 Mil = 0.426
10.77 Mil = 0.5455

So back to my bullet ballistics results... I get the following with a 1:7 Twist barrel (fast twist = bigger drift)
1.82 Mil = 0.07
2.98 Mil = 0.11
4.41 Mil = 0.15
6.14 Mil = 0.2
8.23 Mil = 0.26
10.77 Mil = 0.34

Again... WTF ??? How can I be sooooo far out on drift ?... how much twist do you need ???


I know a lot of guys are against Ballistic Wind reticles, because they are a pain to figure out and calibrate your rifle to them, or it's 'too busy'... but the concept is bloody clever and really should assist with very accurate follow up shots and a hell of a lot less calculating on the range. The major problem is that the manufacturers don't release enough information for us to reliably figure out how to 'true' our ballistics to the reticles... and therefore they shoot themselves in the foot. (as no one wants to buy the scopes).

So in figuring all this out I've built the following excel model CMR-W 556 calibration v3.xlsx if anyone wants to take a look at it.

Which gives the following graph from the data.

Reticle Wind Dots and lines in Dark Blue
Bullet Ballistic's Spin Drift in Cyan (inner)
Bullet Ballistic Wind Dot (JBM calculated) in Cyan (outer)
Bullet Ballistic's Wind Dot lines in Red (Interpolated)
Beaufort Wind Scale (Medians) in Green dashes (based on ballistics)
Black circle = FOV at Maximum zoom
Black dotted circle = FOV at Minimum zoom
Purple circle = Limit of Full Reticle Usage at 1.97x magnification.
Purple dashed circle = Zoom at Application Maximum Distance of 600m = 4.55x magnification.
Purple dotted circle = Zoom at Effective Maximum Distance of 300m = 6.25x magnification.

I also added the Beaufort scale to the file (inc pics), which should help with wind estimations.


So... could anyone please take a look at the above or file and either point out where the hell I'm making a mistake... and if I didn't then what ?

Many thanks

 

[Tactical]

I would play with altitude to find what matches the elevation.

Since most of these are destined for Afghanistan and likely to be used in mountains I would start around 8000 feet.

When I used to teach at 8000 feet I found a M3 dial for 30-06 was super close to my 175s in my 308. I also use a 190 grain 300wm dial for my 155s in a 308. I just use the meter dial as in yards. This works well to a 1000 yards for energy on target but not F Class accuarcy

 

[Redmanss]

I don't have the time to really look at all your data in depth and play with it on JBM, but it looks to me like your initial zero distance is whacky. Level out your zero distance at 300m, then see what your data does. It should balance the rest of your tables, then you can proof it on the range at distance.

 

[Dustoff82]

Reading the Leupold Tactical Milling Reticle manual, it states for the best results zero at 200m, which will allow for the middle dot to serve as the 50m aiming point. Try doing that and let me know. Then I would mess around with altitude as well.

 

[dAyLiTe]

[MENTION=41860]Redmanss[/MENTION] & Dustoff82: Normally I would agree with a 3-9 optic, etc, but this is a 1-6 optic designed for CQB and mid range, and increasing the zero past 100m pretty much makes the scope fairly useless. It's also a scope that is favoured amongst the 3 Gun crowd, so max 'application' distance is really only 300m, with 75% of targets in 50m. By increasing the zero to those ranges, you'll end up holding under, and depending on mount height, that can be loopy 'pun intended'.
[MENTION=203]Tactical[/MENTION]: Totally makes sense. I've messed around and 4000ft / 25c / 29.77inHg pretty much nails the range values. This raises some interesting points regarding ballistic reticles, and I wonder how many shooters understand the effects that altitude and temperatures have on their ballistics. I'm in Cape Town, South Africa at sea level, and Johannesburg is higher than Denver at 5751ft, so we've got a massive spread to work with. I'll do some Pressure Altitude / Temperate & Density Altitude calculations and see just how far out the ballistics move in relation to the reticle.

As the application for this scope is short to medium range and targets of 10" plate at those ranges, there is a wide enough margin of error that a centralised Density Altitude calculation should give a good indication of 'zero'... and therefore 'true'ish the scope at most likely Density Altitude's... that's the theory anyway, now lets see what the data does.

 

[Redmanss]

I think you may be misunderstanding what I meant. The manual actually states to zero at 200m (http://www.leupold.com/wp-content/uploads/2012/07/Tactical-Milling-Reticle-Man.pdf?469fc8). I like to push it out a bit further when I can, which in turn lessens the compounding of errors further downrange. A .5mil difference at 50m is nothing, especially when you're considering taking rapid fire shoot and move shots, where most of us are happy to hold 5moa groups when running 50m controlled pairs. I'm using a CMR-W 7.62 Mark 6 with 77gr SMKs, zeroed at 300m on the 300m mark, and it balances very well for my purposes. No, I'm not taking distant shots with it yet, but inside 400m it's hammering thus far for me, both close and a bit out there. Maybe this coming summer I'll get to stretch its legs a bit further, maybe it will find its way over to my .308, but if I'm playing around trying to bust clays at 600m, I have the .260 bolt gun with the S&B on top.

The DA differences is the weak point of a BDC reticle, but so long as you know what to expect and how to compensate for it, they can be very practical. You don't buy BDC reticles for accuracy, you buy them for speed when close enough is good enough on minute-of-man two way engagements, or seeing how fast you can clean a course of fire on IPSC sized targets. One has to decide if BDC is the way to go for themselves, and luckily there is the TMR-D as an option too.

 

[dAyLiTe]

Yes and No... ... the manual that you're referring to is their generic tactical manual and covers a large range of their scopes and reticles.
The specific CMR-W spec sheet indicates a zero at 50m, which is what you're basically doing with a 300m zero by using the 300m mark at the bottom of horseshoe... nice pickup, it makes sense.

I completely agree with what you're saying on the 0.5Mil at 50m = 10cm on a steel plate of 25cm... it hardly makes a difference.

I guess I'm going a bit OTT, but it's interesting trying to figure out how to get the most out of the CMR-W.
It's also crazy that the manufacturer's don't supply all the data that they used to produce these reticles so that others can modify them to their own requirements.

In addition, in the image/graph above, 100% of the useful/application of the bullet is within 1.34 Mil elevation of the reticle (out to 300m) ... where there aren't even any reticle markings anyway... and yes, beyond 500m, I use my .260 with a S&B too...

I'm pretty interested to know how the 5mph wind dots are matching up with what you're shooting, please let us know.

 

[Redmanss]

0.5mil at 50m is actually 2.5cm, even less of a difference.

I agree with the confusion of what data Leupold used to produce their information, even contradicting themselves on the same image, but I use my own data instead of what they provide. It's only a starting point for me.

I really wish I had enough data to tell you about the wind marks and implementation, but I don't have enough time behind it yet in the wind. Maybe this summer out west as well for that, as the wind is weak in the east on my range there with all the tall oaks and dense undergrowth on either side of it. In talking with some of your fellow countrymen I work with, I know you'll certainly have more open ground wind to deal with.

 

[dAyLiTe]

0.5mil at 50m is actually 2.5cm, even less of a difference.

Doh... I multiplied rather than divided.

Yeah, the wind is certainly a factor here... we average 9-14 knots during a month depending on the time of year, with sustained gust of 36-45 knots.

Many thanks for the input.

 

[Dustoff82]

The manual clearly states to zero at 200m for it to be more accurate on the reticle...im not arguing with you just to argue. Im doing that because I recently purchased the exact same scope (which I have not yet used), and will be using it for the exact same application (so yes I know what distances 3gun shoots are primarily at). I want you to test out a 200m zero like the manual says so I can find out how accurate this reticle really is.

 

[dAyLiTe]

lol... looking back at their wording, we're all right.
The CMR-W 5.56 spec sheet says: "5.56 NATO/.223 Remington - 62 gr. - 2970 fps - 50 meter Zero"
The generic manual states: "For best results, the CM-RW reticle should be zeroed at 200 meters, allowing the center point of the reticle to also serve as a 50 meter aiming point."

So by zeroing at 200m, you are also in effect zeroing at 50m... better make sure you have the right 'zero'.

ok, so that pulls the data in much closer.

 

[Dustoff82]

Which is exactly why I wanted you to try it. Now how close is the data compared to your previous data?

 

[dAyLiTe]

0.86 Mil = 303m (vs 300m)
1.82 Mil = 395m (vs 400m)
2.98 Mil = 487m (vs 500m)
4.41 Mil = 580m (vs 600m)
6.14 Mil = 672m (vs 700m)
8.23 Mil = 764m (vs 800m)
10.77 Mil = 858m (vs 900m)

... so elevation is a huge amount better, probably just need a tiny temp / altitude adjustment and we're there.

 

[JL]

I've got same reticle on top of 16" carbine- did some calculations too for Fed XM193 ammo.

Within rifles practical operating range, to 500-600m, reticle "error" is minuscule.
Interestingly enough, winds are mph but elevation is metric. Doesent really matter though because mps is close to 0.5x mph.

Overall I like scope and reticle.

 

[dAyLiTe]

Right, we're getting there:

Temperature: 25c
Barometric Pressure 29.77 inHg
Altitude: 2500 ft
Wind 32.1
Zero: 200m
Barrel Twist: 1:7

Gives:
-1.818 - 403m (vs 400m)
-2.977 - 500m (vs 500m)
-4.415 - 600m (vs 600m)
-6.149 - 699m (vs 700m)
-8.245 - 798m (vs 800m)
-10.767 - 898m (vs 900m)

Which looks like:

Here is the excel file: CMR-W 556 calibration v4.xlsx

So things are looking great on the elevation, but still a bit off on the Spin Drift.

Note: the difference between the yellow line and the cyan line next to it.
The cyan line is the calcualted ballistic Spin Drift, and the Yellow line is the reticles Spin Drift.
As you can see, the whole graph needs to be shifted right to get it to align 100%.
i.e. more ballistic spin drift is needed on the bullet... but more than 1:7 is a bit ridiculous.

Any one got any further ideas on how they would have achieved such high Spin Drift figures ?
- Even if I don't enable 'Windage Correction for Zero Range' in JBM at 0 Wind to calculate Spin Drift, it's still not quite enough Drift (although very close).
- So did they forget to remember that when they calculate Spin Drift, that they need to adjust it Left so that Spin Drift is Zero'ed at 200m. ? hmmm ?

 

[farmerbrown]

Right, we're getting there:

Temperature: 25c
Barometric Pressure 29.77 inHg
Altitude: 2500 ft
Wind 32.1
Zero: 200m
Barrel Twist: 1:7

Gives:
-1.818 - 403m (vs 400m)
-2.977 - 500m (vs 500m)
-4.415 - 600m (vs 600m)
-6.149 - 699m (vs 700m)
-8.245 - 798m (vs 800m)
-10.767 - 898m (vs 900m)


So things are looking great on the elevation, but still a bit off on the Spin Drift.

That's awesomely close...

I haven't looked into the wind/spin drift - perhaps I should.
I'll have a look at your spread-sheet in the next day or so and see if I can figure it out.

I'm interested because I have the same scope for .308 (175 gn HPMK at 2575fps/785 ms)

I also have it zeroed at 50 meters - I also saw the mixed message on the 200 meter zero

I played with the elevation and found that the figures worked best about 550 meters elevation or 1800 f)
Temp was 15 C (59 F) - I didn't try too much harder than this.

Hope that helps...
Cheers
Farmer

 

[dAyLiTe]

So the reticle indicates Spin Drift in Mil at:
1.82 Mil = 0.148
2.98 Mil = 0.1985
4.41 Mil = 0.2525
6.14 Mil = 0.343
8.23 Mil = 0.426
10.77 Mil = 0.5455

and with the new inputs I'm now getting:
1.82 Mil = 0.06 (difs 0.088)
2.98 Mil = 0.09 (difs 0.1085)
4.41 Mil = 0.14 (difs 0.1125)
6.14 Mil = 0.19 (difs 0.153)
8.23 Mil = 0.25 (difs 0.176)
10.77 Mil = 0.33 (difs 0.2155)

This is really splitting hairs a bit, as 0.088 Mil at 400m is only 3.52cm, and 19.395cm at 900m.
...however it does irritate me enough to still ponder why there would be such a difference.

Any ideas ?

 

[Redmanss]

50m does line up with 200m for zeroing ballisticly, but 50m zeroing is for when shooters or military units are limited to close ranges for sighting in weapons prior to taking them into the field. I've done a LOT of close range zeroing, and have witnessed that shooter error is much more likely to come up there showing deviations compounded down range. Zero in at the furthest distance you practically can.

 

[dAyLiTe]

The atmospheric variables above are giving me a Density Altitude of 4600ft, which sort of put it at a yearly average of somewhere between Denver (DA:5800ft) and Las Vegas (DA:3400ft)... which seems a bit high for general US usage (as per 'Tactical's initial comments).

I'm still no closer to figuring out how Leupold got to the Spin Drift values that they have for the scope.

To give you an idea, with the Reticle Spin drift being so high, it throws the calculations out by the following cm values:

<table cellspacing="0" cellpadding="0"> <col width="104" /> <col width="72" /> <col width="89" span="7" /> <col width="98" /> <col width="89" span="4" /> <tr> <td colspan="11"><div align="center">Difference between Reticle Wind Dot and Bullet Wind Dots at Bullet Range in Centimeters</div></td> </tr> <tr> <td width="89" bgcolor="#CCCCCC"><div align="center"><strong>Elev Mils</strong></div></td> <td width="89" bgcolor="#CCCCCC"><div align="center"><strong>Range</strong></div></td> <td width="89" bgcolor="#CCCCCC"><div align="center"><strong>-4</strong></div></td> <td width="89" bgcolor="#CCCCCC"><div align="center"><strong>-3</strong></div></td> <td width="89" bgcolor="#CCCCCC"><div align="center"><strong>-2</strong></div></td> <td width="89" bgcolor="#CCCCCC"><div align="center"><strong>-1</strong></div></td> <td width="98" bgcolor="#CCCCCC"><div align="center"><strong>0</strong></div></td> <td width="89" bgcolor="#CCCCCC"><div align="center"><strong>1</strong></div></td> <td width="89" bgcolor="#CCCCCC"><div align="center"><strong>2</strong></div></td> <td width="89" bgcolor="#CCCCCC"><div align="center"><strong>3</strong></div></td> <td width="89" bgcolor="#CCCCCC"><div align="center"><strong>4</strong></div></td> </tr> <tr> <td align="right"><div align="center">-1.818</div></td> <td align="right"><div align="center">403 m</div></td> <td align="right"><div align="center">-12.45</div></td> <td align="right"><div align="center">-10.12</div></td> <td align="right"><div align="center">-8.26</div></td> <td><div align="center"></div></td> <td><div align="center">3.53</div></td> <td align="right"><div align="center">-1.09</div></td> <td align="right"><div align="center">1.01</div></td> <td align="right"><div align="center">3.26</div></td> <td align="right"><div align="center">5.36</div></td> </tr> <tr> <td align="right"><div align="center">-2.977</div></td> <td align="right"><div align="center">500 m</div></td> <td align="right"><div align="center">-16.40</div></td> <td align="right"><div align="center">-13.60</div></td> <td align="right"><div align="center">-10.55</div></td> <td align="right"><div align="center">-8.10</div></td> <td><div align="center">5.23</div></td> <td align="right"><div align="center">-2.20</div></td> <td align="right"><div align="center">0.60</div></td> <td align="right"><div align="center">2.85</div></td> <td align="right"><div align="center">5.55</div></td> </tr> <tr> <td align="right"><div align="center">-4.415</div></td> <td align="right"><div align="center">600 m</div></td> <td align="right"><div align="center">-18.72</div></td> <td align="right"><div align="center">-16.02</div></td> <td align="right"><div align="center">-12.90</div></td> <td align="right"><div align="center">-10.08</div></td> <td><div align="center">6.99</div></td> <td align="right"><div align="center">-3.60</div></td> <td align="right"><div align="center">-1.08</div></td> <td align="right"><div align="center">1.26</div></td> <td align="right"><div align="center">5.22</div></td> </tr> <tr> <td align="right"><div align="center">-6.149</div></td> <td align="right"><div align="center">699 m</div></td> <td align="right"><div align="center">-24.88</div></td> <td align="right"><div align="center">-21.25</div></td> <td align="right"><div align="center">-17.89</div></td> <td align="right"><div align="center">-13.63</div></td> <td><div align="center">10.75</div></td> <td align="right"><div align="center">-7.20</div></td> <td align="right"><div align="center">-3.49</div></td> <td align="right"><div align="center">-1.12</div></td> <td align="right"><div align="center">3.50</div></td> </tr> <tr> <td align="right"><div align="center">-8.245</div></td> <td align="right"><div align="center">798 m</div></td> <td align="right"><div align="center">-33.12</div></td> <td align="right"><div align="center">-28.81</div></td> <td align="right"><div align="center">-23.62</div></td> <td align="right"><div align="center">-19.31</div></td> <td><div align="center">14.26</div></td> <td align="right"><div align="center">-9.50</div></td> <td align="right"><div align="center">-4.71</div></td> <td align="right"><div align="center">-0.08</div></td> <td align="right"><div align="center">5.03</div></td> </tr> <tr> <td align="right"><div align="center">-10.767</div></td> <td align="right"><div align="center">898 m</div></td> <td align="right"><div align="center">-36.37</div></td> <td align="right"><div align="center">-31.43</div></td> <td align="right"><div align="center">-26.58</div></td> <td align="right"><div align="center">-22.90</div></td> <td><div align="center">18.78</div></td> <td align="right"><div align="center">-14.37</div></td> <td align="right"><div align="center">-10.42</div></td> <td align="right"><div align="center">-5.84</div></td> <td align="right"><div align="center">-2.33</div></td> </tr> </table>
So, it's not so bad when you're shooting in a Left to Right wind (right side), but it gets hinky when shooting in Right to Left wind (left side).

I've emailed Leupold... but got absolutely no response so far.


Here are the inputs that I'm using in JBM in case I've done something stupid:

Ballistic Coefficient: 0.304 G1
Bullet Weight: 62gr
Caliber: 0.224

Bullet Length: 0.907 inches
Plastic Tip Length: 0.0

Muzzle Velocity: 2970ft/s
Distance to Chronograph: 3m

Sight Height: 1.5 inches
Sight Offset: 0.0
Zero Height: 0.0
Zero Offset: 0.0
Windage: 0.0
Elevation: 0.0
Line Of Sight Angle: 0.0
Cant Angle: 0.0
Barrel Twist: 7 inches
Twist Direction: Right

Wind Speed 0 ... but use 8.05 kmh (5mph) when calculating Wind not Drift.
Wind Angle: 90

Target Speed: 0
Target Angle: 0
Target Height: 12.0 (default)

Minimum Range: 0
Maximum Range: 1200
Range Increment: 1
Zero Range: 200

Temperature: 25c
Pressure: 1008.13
Humidity: 0.0
Altitude
Std. Atmosphere at Altitude: unchecked
Pressure is Corrected: checked

Vital Zone Radius: 10cm
"Energy Column" Formula: Energy (ft/lbs)
Column 1 Units: 0.1 mil
Column 2 Units: 0.1 cm
Elevation Correction for Zero Range: checked
Windage Correction for Zero Range: checked *(see note below)
Ranges in Meters: checked
Target Relative Drops: checked
Zero at Max. Point Blank Range: unchecked
Mark Sound Barrier Crossing: checked
Include Extra Rows: unchecked
Round Output to Whole Numbers: unchecked
Include Spin Drift: checked
Include Danger Space: unchecked


Note: I've set 'Windage Correction for Zero Range' to checked, ONLY when calculating the Spin Drift, and it is unchecked when calculating Wind thereafter. This ensures that the scope is zero'ed correctly including Spin Drift, and allows for the removal of Spin Drift from the Wind Dot value calculation (Wind - SpinDrift = WindDot offset).

Anyone got any bright ideas on how Spin Drift could be so high as per the reticle ?
1.82 Mil = 0.148
2.98 Mil = 0.1985
4.41 Mil = 0.2525
6.14 Mil = 0.343
8.23 Mil = 0.426
10.77 Mil = 0.5455

???

 

[Dustoff82]

Can you keep all the other info the same and input like 1000ft and 1500ft info for me please?

 

[farmerbrown]

What about sight height?

Many ballistics programs default to 1.5" but it's commonly much more than this these days. It's 7.8 cm on my MR308 or almost three inches.

Who knows what Leupold used, but likely much more than 1.5"?

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[FLIGHT762]

What about sight height?

Many ballistics programs default to 1.5" but it's commonly much more than this these days. It's 7.8 cm on my MR308 or almost three inches.

Who knows what Leupold used, but likely much more than 1.5"?

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Exactly, he needs to input the proper sight height. likely around 2.8"+

 

[JL]

Here is the excel file: CMR-W 556 calibration v4.xlsx

So things are looking great on the elevation, but still a bit off on the Spin Drift.

Note: the difference between the yellow line and the cyan line next to it.
The cyan line is the calcualted ballistic Spin Drift, and the Yellow line is the reticles Spin Drift.
As you can see, the whole graph needs to be shifted right to get it to align 100%.
i.e. more ballistic spin drift is needed on the bullet... but more than 1:7 is a bit ridiculous.

May I ask why you used kilometers per hour as secondary wind unit?

 

[dAyLiTe]

[MENTION=92064]farmerbrown[/MENTION], Flight762: Sight height makes absolutely no difference to Spin Drift from the perception of the scope.

@JL: I'm in Cape Town, South Africa... we use the metric system. Some of the variables I have used are in imperial, merely because of the sources that I got the data from. (btw: http://timetric.com is a brilliant source for historical temp & pressure data).
[MENTION=52068]Dustoff82[/MENTION]: I'll post an update of the file, and instructions on how to use it with data from JBM, then you can mess around as you like.

 

[farmerbrown]

[MENTION=92064]farmerbrown[/MENTION], Flight762: Sight height makes absolutely no difference to Spin Drift from the perception of the scope.

I understand that (unless you have wind and cant). Just pointing out (since you seem to be on a mission to recreate the Leupold numbers) that this is one factor (which makes quite a bit of difference) which seems as though it could be either:

1. Disagreeing with the Leupold number or

2) unlikely to be correct since I'd expect this scope to be mounted on platforms in such a way as to be considerably higher as flight762 confirms.

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[dAyLiTe]

Sorry, what I meant was that I did change it to 7.8cm, and it made no difference to the figures... I do appreciate the suggestions.

I guess it is a 'bit of a mission', and again apologies for the OCD... but if I can't get to the original 'baseline' that Leupold has set in creating this scope, how can I trust my inputs going forward ? i.e. I've got to a point where I'm stuck and it seems it's only Spin Drift... and I'm trying to figure out if I'm wrong (more likely), or they made a mistake (less likely).

I also completely understand that the adjustments that I'm looking at are 'honestly' outside of the scope of operation for which this reticle was intended (although it is designed to handle it).

I'm in no way a 'ballistician' or the like, so there is the likelihood that I have made a mistake... and I'm really just asking for help to see where I've gone wrong. (There are not a lot of other forums that would even understand the problem in the first place.)

Ultimately I'm hoping to get to pretty much 'exactly' the Leupold numbers achieved, so that I can then change out with a different bullet at my density altitude (660ft) and get that 'trued' so that I can use it most effectively in our local high wind environment... then everyone could use my excel doc to do the same for their local variables.

Couple of other things I can try:
- I could change the density altitude and then change the muzzle velocity. (that might help with Drift).
- I've seen slightly different figures for BC of the M855: 0.304 G1, 0.303 G1, 0.273 G1 and 0.151 G7, 0.134 G7 @ 3270fps.

Thanks for the help so far, please keep it coming...

 

[farmerbrown]

Hi,

Yes, sorry, I was only talking about sight height affecting elevation - I tried to replicate their 7.62 numbers (see above) and never got that close before losing interest/motivation.
I'm not that interested in windage - I don't have a huge wind problem, normally - will relook at it with what you've done here.

But, I basically figured 'close enough' and tried to get the projectile to basically follow the curve.
With the complete drought of Varget and 175 HPMK around here, I've had to do some projectile substitution.
That's why I look at using the Lapua 170 FMJBT at 791 m/s which seems quite close out to subsonic range (900-1000 meters)

My theory is basically that I'm not after a first round hit - it's a quick target acquisition, use reticule, fire shot and should be within a 50-100 cm radius - correct and impact.

Seems to work so far out to the 700 plus I've tried it.

 

[ctay20]

Ultimately I'm hoping to get to pretty much 'exactly' the Leupold numbers achieved, so that I can then change out with a different bullet at my density altitude (660ft) and get that 'trued' so that I can use it most effectively in our local high wind environment... then everyone could use my excel doc to do the same for their local variables.

Any update? I'm using the 7.62 reticle with 5.56 and hoping to modify your spreadsheet to the 7.62 reticle and adjust appropriately for my 5.56 load. I have also had trouble recreating the 7.62 reticle - basically exactly the same issues you have found with the 5.56.

 

[dAyLiTe]

Nope... no further luck.
...and no answers to my emails to Leupold. (I even tried their 'tactical optics' division.).

I've tried using data from New York (13ft elevation) in the middle of winter with a density altitude of -3300ft, and Denver (5280ft elevation) in summer with a density altitude of 9050ft... and it doesn't make even 10% difference to spin drift... let alone the 200% difference needed to 'true' it.
Neither does messing with the G1 BC between .279 and .304.

I'm really starting to think that Leupold screwed up on this one, and forgot to adjust for 'spin drift' in their windage Zero calculation, and added it instead... although, even then it's not quite enough. It's almost like they doubled their spin drift figures.


However; What is fairly amazing is how wide spread the data is between New York (Winter) and Denver (Summer)... at -10.767 Mil of elevation, the M855 @ 2790fps gets to 810m in New York (Winter), and 965m in Denver (Summer)... which also completely messes with the 5mph reticle Wind Dots, especially in New York.

So... if you're not living at 4500ft density altitude where it seems this scope was calibrated at... then make sure you calibrate your CMR-W reticle, otherwise it ain't going to help you get even close to what the manual says.


I've pretty much lost interest in chasing this down any further, as I bought the 1-6 scope and CMR-W 5.56 reticle for '3 Gun Nation' competition, so the targets that I'm going to be shooting are all inside 300m and inside the nice big horseshoe (which I really like), and therefore not a big problem with the wind dots that go from 400m+.
We also have to ask ourselves... shooting past 600m (3rd Wind Dot row) at a maximum of 6x magnification (in teh 1-6 scope), is like shooting 100m+ with Iron Sights... is that 'really' in the intended application of this scope and reticle. I would say no... as I expect most people are 'comfortable' with Iron Sights out to 50m 'maybe'... so are the Wind Dots applicable... in this case, probably not.


This is not the case for the Leupold Mark 6 3-18x44mm M5B2, which is probably going to suffer the most with these reticles... especially in 7.62. I'll work it out for the 7.62 version, but I suspect that it's not going to be pretty, as the further out Wind Dots will then be needed...

...I'm still hoping someone is going to point out an error in my calculations/variables, and it then 'works'...

 

[dAyLiTe]

I've worked out the CMR-W 7.62 as well... and the Spin Drift is pretty much spot on to the calculated figures... so seems that they got this one right.

From the info that I've found online, it 'seems' that a Sierra MatchKing HPBT 175gr was used as the calibration round.

I've got it fairly close to indicated distance at 5100ft density altitude and at 2450fps: (which seems a little low)
<table cellspacing="0" cellpadding="0"> <col width="84" span="3" /> <col width="82" /> <tr> <td width="84" align="right" bgcolor="#CCCCCC"><strong>Elev (Mil)</strong></td> <td width="84" align="right" bgcolor="#CCCCCC"><strong>Reticle (m)</strong></td> <td width="84" align="right" bgcolor="#CCCCCC"><strong>Bullet (m)</strong></td> <td width="82" align="right" bgcolor="#CCCCCC"><strong>Difs (m)</strong></td> </tr> <tr> <td align="right">-2.43</td> <td align="right">400</td> <td align="right">422</td> <td align="right">-22</td> </tr> <tr> <td align="right">-3.67</td> <td align="right">500</td> <td align="right">514</td> <td align="right">-14</td> </tr> <tr> <td align="right">-5.09</td> <td align="right">600</td> <td align="right">607</td> <td align="right">-7</td> </tr> <tr> <td align="right">-6.69</td> <td align="right">700</td> <td align="right">701</td> <td align="right">-1</td> </tr> <tr> <td align="right">-8.51</td> <td align="right">800</td> <td align="right">796</td> <td align="right">4</td> </tr> <tr> <td align="right">-10.61</td> <td align="right">900</td> <td align="right">894</td> <td align="right">6</td> </tr> <tr> <td align="right">-13.01</td> <td align="right">1000</td> <td align="right">994</td> <td align="right">6</td> </tr> <tr> <td align="right">-15.78</td> <td align="right">1100</td> <td align="right">1097</td> <td align="right">3</td> </tr> <tr> <td align="right">-18.93</td> <td align="right">1200</td> <td align="right">1189</td> <td align="right">11</td> </tr> </table>
For Spin Drift, I'm getting almost identical figures:
<table cellspacing="0" cellpadding="0"> <col width="82" /> <col width="90" span="2" /> <col width="76" /> <tr> <td width="82" align="right" bgcolor="#CCCCCC"><strong>Elev (Mil)</strong></td> <td width="90" align="right" bgcolor="#CCCCCC"><strong>Reticle (mil)</strong></td> <td width="90" align="right" bgcolor="#CCCCCC"><strong>Bullet (mil)</strong></td> <td width="76" align="right" bgcolor="#CCCCCC"><strong>Difs (mil)</strong></td> </tr> <tr> <td align="right">-2.43</td> <td align="right">0.07425</td> <td align="right">0.07</td> <td align="right">0.004</td> </tr> <tr> <td align="right">-3.67</td> <td align="right">0.11</td> <td align="right">0.1</td> <td align="right">0.010</td> </tr> <tr> <td align="right">-5.09</td> <td align="right">0.12825</td> <td align="right">0.13</td> <td align="right">-0.002</td> </tr> <tr> <td align="right">-6.69</td> <td align="right">0.16275</td> <td align="right">0.18</td> <td align="right">-0.017</td> </tr> <tr> <td align="right">-8.51</td> <td align="right">0.19975</td> <td align="right">0.22</td> <td align="right">-0.020</td> </tr> <tr> <td align="right">-10.61</td> <td align="right">0.23575</td> <td align="right">0.27</td> <td align="right">-0.034</td> </tr> <tr> <td align="right">-13.01</td> <td align="right">0.2815</td> <td align="right">0.33</td> <td align="right">-0.049</td> </tr> <tr> <td align="right">-15.78</td> <td align="right">0.33925</td> <td align="right">0.4</td> <td align="right">-0.061</td> </tr> <tr> <td align="right">-18.93</td> <td align="right">0.3879</td> <td align="right">0.47</td> <td align="right">-0.082</td> </tr> </table>
For Wind Dots, I had to use 9mph to get it to line up, not the indicated 10mph:
<table cellspacing="0" cellpadding="0"> <col width="84" span="3" /> <col width="82" /> <tr> <td width="84" align="right" bgcolor="#CCCCCC"><strong>Elev (Mil)</strong></td> <td width="84" align="right" bgcolor="#CCCCCC"><strong>Reticle (mil)</strong></td> <td width="84" align="right" bgcolor="#CCCCCC"><strong>Bullet (mil)</strong></td> <td width="82" align="right" bgcolor="#CCCCCC"><strong>Difs (Mil)</strong></td> </tr> <tr> <td align="right">-2.43</td> <td align="right">0.867</td> <td align="right">1.03</td> <td align="right">-0.16</td> </tr> <tr> <td align="right">-3.67</td> <td align="right">1.176</td> <td align="right">1.29</td> <td align="right">-0.11</td> </tr> <tr> <td align="right">-5.09</td> <td align="right">1.464</td> <td align="right">1.59</td> <td align="right">-0.13</td> </tr> <tr> <td align="right">-6.69</td> <td align="right">1.821</td> <td align="right">1.91</td> <td align="right">-0.09</td> </tr> <tr> <td align="right">-8.51</td> <td align="right">2.187</td> <td align="right">2.25</td> <td align="right">-0.06</td> </tr> <tr> <td align="right">-10.61</td> <td align="right">2.58</td> <td align="right">2.63</td> <td align="right">-0.05</td> </tr> <tr> <td align="right">-13.01</td> <td align="right">3.018</td> <td align="right">3.03</td> <td align="right">-0.01</td> </tr> <tr> <td align="right">-15.78</td> <td align="right">3.452</td> <td align="right">3.45</td> <td align="right">0.00</td> </tr> <tr> <td align="right">-18.93</td> <td align="right">3.8866</td> <td align="right">3.84</td> <td align="right">0.05</td> </tr> </table>
Which gives:

Grab the 'CMR-W 762 calibration v8.xlsx' excel file here if you want to use it to calibrate your CMR-W 7.62 reticle for your rifle where you live.

It's not quite 100% perfect, but damn close, and I'm not sure my shooting would 'notice' the tolerances

 

[farmerbrown]

Hi,

Yes, the info I have is that it's a 175 HPMK at 2575 fps, but I can only really get it to agree by using about 550 meters elevation as I showed above...

Thanks for the Excel.

 

[dAyLiTe]

What is your density altitude range ?
Although I'm at 45m Elevation, I've got a density altitude range of -480m up to 2900m, so it's really all over the place... with a mean of 130m... so I'll readjust mine to that, and either:
1. ignore the ballistic reticle and work off my own distances... (or)
2. zero at a different distance to bring it closer to my bullet ballistics.

 

[ctay20]

thank you for the excel - very helpful!

 

[Redmanss]

Are you breaking down and collecting your data from a drawing or an actual photo of the reticle? Some drawings are not as "to scale" as others. Thinking out loud here...

 

[dAyLiTe]

I've picked up the data from the PDF docs (images) that Leupold has published, then open the PDF files in Adobe Illustrator, then lined the reticle up with the left/top edge and scale it so that 20Mil = 200mm. Each vector point can then easily be read. Illustrator gives you 3 decimal place accuracy on each vector point, so the data is very accurate vs a bitmap... 'if it is actually the reticle data, and not some marketing image'... so yes, that could be the problem (garbage in = garbage out), and I initially suspected as much.

However; the rest of the data is spot on, and only the Spin Drift is off on the CMR-W 5.56 by a scale of around 200% per Wind Dot line, so it's not linear... which I would find hard to understand why they would take the time to rebuild the reticle for marketing purposes and be a specific vertically non-linear scaled value out on Spin Drift. In addition; when I lined up & scaled the CMR-W 5.56 using the 20Mil horizontal stadia, all the vertical elevation stadia were within 2 decimal places the same as published.

The CMR-W 7.62 published pdf image on the other hand has been vertically scaled down slightly by Leupold for marketing/layout purposes (?) to fit better on a page, and needed to be stretched vertically to get it correct. (not that I needed to, as the elevation data is supplied).

I just wish that Leupold would respond and confirm the Wind Dot Mil data as well as the reference data for the bullet. The only people that they are shooting in the foot are themselves, as it merely drives people away from their product. ... it's quite frustrating.

 

[dAyLiTe]

Great news: Leupold got back to me !

Ok, looks like the data that I pulled from the published data pdf's was pretty spot on (to their complete surprise).
They used a few different environmental variables, but the main contributor to Spin Drift difference was a 45 degree latitude Coriolis Effect that they have included.
Great for you guys in the US, but for the rest of us in the Southern Hemisphere... not quite so great... although it's great to know that if you do invade, your scopes won't work...

I also had to switch to the Applied Ballistics online ballistic calculator rather than JBM, as JBM does not calculate for the Coriolis Effect. The switch to the different solver, could also account for a difference in the figures.

Once I've got the data 'trued' to the reticle and bounced it off Leupold, I'll post another set of files.

 

[xCavalryx]

Great for you guys in the US, but for the rest of us in the Southern Hemisphere... not quite so great... although it's great to know that if you do invade, your scopes won't work...

Well shoot, that screws up all of our plans! LOL

 

[SNIPERS4DUMMIES]

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