| Distance | Mill Size | 36 Inch |
|---|---|---|
| Yards | Inch | Mills |
| 1000 | 36.000 | 1.000 |
| 950 | 34.200 | 1.053 |
| 900 | 32.400 | 1.111 |
| 850 | 30.600 | 1.176 |
| 800 | 28.800 | 1.250 |
| 750 | 27.000 | 1.333 |
| 700 | 25.200 | 1.429 |
| 650 | 23.400 | 1.538 |
| 600 | 21.600 | 1.667 |
| 550 | 19.800 | 1.818 |
| 500 | 18.000 | 2.000 |
| 450 | 16.200 | 2.222 |
| 400 | 14.400 | 2.500 |
| 350 | 12.600 | 2.857 |
| 300 | 10.800 | 3.333 |
| 250 | 9.000 | 4.000 |
| 200 | 7.200 | 5.000 |
| 150 | 5.400 | 6.667 |
| 100 | 3.600 | 10.000 |
| 50 | 1.800 | 20.000 |
Don't have the latest newfangled range finder, ballistic pull-up scope and such? If you have a variable powered scope, there's a lot that you can do with it.
Looking at fig. 1 to the left we can see that a target with a 36 inch diameter has an angle of 1 mill at 1000 yards and 2 mills at 500 yards. Also a target with an 18 inch diameter has an angle of 1 mill at 500 yards. You can multiple by 2 and get 2 mills at half the distance (250 yards) or 0.5 mills at twice the distance (1000 yards). Double the distance and half the angle in mills is a convenient rule of thumb.
For this to be useful you must be able to measure a mill with your scope. Some scopes have a mildot reticle, most don't. The scope reticle shown below with narrow cross-hairs in the center and wider lines away from the center is common. Even though this type of retical doesn't have mill dots it has something that can serve the purpose.
You can make a device by drawing squares that are correct for mill sizes if interest at a range that is convenient for your trials (no shooting, you can do it inside) to check your scope. The formula is: opposite (inches) = tangent (radians) x adjacent (inches) so at 20 feet we have:
| 20 x 12 x 1 x 0.001 = 0.240 inch = 1 mills at 20 feet. |
| 20 x 12 x 2 x 0.001 = 0.480 inch = 2 mills at 20 feet. |
| 20 x 12 x 4 x 0.001 = 0.960 inch = 4 mills at 20 feet. |
| 20 x 12 x 8 x 0.001 = 1.920 inch = 8 mills at 20 feet. |
For the scope reticle in the box at the top left of fig. 2 there are three references; [full] the distance from the narrow line end to end shown on the second row, [half] the distance from the end of the thin line to the intersecting line shown on the third row (note: this is the smallest actual marked reference), and [quarter] the distance from the point half way between the end of the thin line and the intersecting line to the intersecting line shown on the fourth row. Your scope most likely has this, or some other distinguishing features that can be used.
The chart shows the results from 3x to 9x for a 3-9 variable scope and 12x. At 12x the intersecting cross hair and the end of the thin part of the cross hair equals one mill. This is not some happy accident, but is by design from the manufacturer of the scope although they may not have told you since they'd like to sell you a more expensive scope. Even though the 3-9 scope does not have a 12x magnification, the rule of thumb about double and half lets us translate it to 6x without much thought. Notice that 3x, 4x, 6x, and 8x have easy to remember numbers (at least on the example scope). You must determine the values for your scope as described above if the manufacturer did not state what marks and magnification equal a mill in the manual.
Just as double the distance and half the angle in mills was a rule of thumb for distance vs. mills, so too is double the magnification and half the angle in mills. If you know that at 12x, the distance between the smallest marks (end of narrow cross hair and intersecting cross hair, you can determine the number of mills between those points at other magnifications. One mill at 12 x is two mills at 6x. This is exactly the same as for scope with mill dot reticles.
|
3x | 4x | 5x | 6x | 7x | 8x | 9x | 12x |
|---|---|---|---|---|---|---|---|---|
|
8 | 6 | 4.8 | 4 | 3.43 | 3 | 2.67 | 2 |
|
4 | 3 | 2.4 | 2 | 1.71 | 1.5 | 1.33 | 1 |
|
2 | 1.5 | 1.2 | 1 | 0.86 | 0.75 | 0.67 | 0.5 |
We must use the same units throughout a formula. Inches were fine for making our reference targets above but for use in the field we will use yards. A convenient formula that doesn't take too much thinking is: (estimated height of target in yards x 1000) / height of target in mills.
As an example if your target is a deer where the back to chest height is 18 inches, the height of the target in yards is 0.5. If it appeared in your reticle as one mill it would be 500 yards away (see fig 1). If it appeared as 1.5 mills then 0.5 x 1000 / 1.5 = 333.3 yards range. Or if it was 1.25 mills then 0.5 x 1000 / 1.25 = 400 yards. Yes, there will be errors since you are estimating the height of the target and the number of mills that you see, but it is better than you can do with a wild guess.
To use this information you must get data for your rifle and load. At the time of this writing there' a very nice web based calculator at www.handloads.com/calc. If it goes away, as things on the web do, search engines are your friend.
With the data obtained from the drop tables, and the information found here, you can make a table like the one in fig. 3 that follows. This table uses distances that go out to the limits of ethical hunting with this load. The rifle, scope, and load are clearly for large game at medium distances.
You can make a chart like this, or one that goes out to fantasy distances, as you wish. Calculate drop and drift by dividing drop or drift in inches by the size of a mill at that range from fig. 1. For example, at 100 yds the bullet strike is 3.45 inches high and one mill is 3.6 inch so 3.45 / 3.6 = 0.96 (your hold over is about 1 mill).
To add the column for leading a moving target you use the time of flight (TOF) for that range along with the number of inches per mill from fig 1. 1 MPH = 1.466667 ft/sec = 17.6 in/sec. So the formula is lead in mill per MPH = TOF / (17.6 / inch per mill). For example at 350 yds the TOF is 0.45 sec and there are 12.6 inches per mill so lead in mills = 0.45 / (17.6 / 12.6) = 0.45 / 1.4 = 0.32 mills.
| RangeYards | Impact Inch |
Impact Mills |
Drift 10 mph Inch |
Drift 10 mph Mills |
TOF sec. |
Lead 1 mph Mills |
|---|---|---|---|---|---|---|
| 0 | -1.50 | NA | 0 | 0 | 0 | 0 |
| 50 | 1.65 | 0.92 | 0.55 | 0.33 | 0.06 | 0.01 |
| 100 | 3.45 | 0.96 | 0.92 | 0.26 | 0.12 | 0.02 |
| 150 | 3.81 | 0.64 | 1.54 | 0.29 | 0.18 | 0.06 |
| 200 | 2.70 | 0.38 | 2.41 | 0.33 | 0.25 | 0.10 |
| 250 | 0 | 0 | 3.55 | 0.39 | 0.31 | 0.16 |
| 300 | -4.34 | -0.40 | 4.96 | 0.46 | 0.38 | 0.23 |
| 350 | -10.41 | -0.83 | 6.66 | 0.53 | 0.45 | 0.32 |
| 400 | -18.30 | -1.27 | 8.65 | 0.60 | 0.52 | 0.43 |
| 450 | -28.10 | -1.73 | 10.95 | 0.68 | 0.59 | 0.54 |
| 500 | -39.92 | -2.22 | 13.56 | 0.75 | 0.66 | 0.68 |
| 550 | -53.85 | -2.72 | 16.51 | 0.83 | 0.74 | 0.83 |
| 600 | -70.02 | -3.24 | 19.79 | 0.92 | 0.82 | 1.01 |
| 650 | -88.54 | -3.78 | 23.44 | 1.00 | 0.90 | 1.20 |
We all know that the rock steady scope views with the target right under the cross-hairs in movies are total BS. In real life our target won't be exactly at the range that we sighted our rifles at, the wind may be blowing and estimating it's speed is difficult. And of course, we have wobble. At 9x, even off a sandbag rest I can see my pulse in the cross-hairs, and it's distracting. The table at fig. 3 has far more accuracy than we can hold, estimate the fractions of a mill, or accurately estimate the true size of the target, all of which contribute to error.
Having said that, the mill dot system has great advantage for those who know how to use it. Managing holdover, lead, and drift in mills is easier than trying to do it in inches. For the rifle and scope shown above, sighted in at the range shown, mill adjustments in aim are within a manageable value within the expectations of the table.
For a 400 yard shot the holdover would be approximately 1.25 mills and a 8 mph crosswind would call for a about 0.5 mill adjustment. That doesn't look like much, but at that range it's an 18 inch elevation correction and a 7.2 inch windage correction. Less than perfect, but better than otherwise under hunting conditions and in this case, the difference in a miss and a hit.
I don't care to copy stuff from other people's web pages so if you want to know about estimating wind speed or target speed, search engines are your friend. This article is focused on how you can use a standard variable power scope to do things that are normally reserved for more specialised, and expensive scopes. Money is tight, learn to use what you've got.
So there we have the mill dot system with a non-mill dot scope, or a mill dot scope for that matter. The mill system is based upon angles so it is attractive to shooters because it provides a consistent scope picture reference for range, drop, wind, and lead computation that is practical in the field. Happy shooting.