In part 1 and part 2 of this series, we discussed the fundamentals of high angle shooting, or slope dope. We spent time talking about the theory and concept of how to compensate for high angle shooting and then talked about methods to measure the angle. We wanted to conclude our discussion on this topic by discussing a new method and an alternate method for slope dope compensation.
The New Method
The methods that we discussed in the previous parts have been taught for many years and generally it will get you pretty close. But through years of study and examination it was determined that it is not totally accurate. Let us just get one thing clear right now though, there is no substitute for data that you gather yourself for your particular rifle and ammunition. That is why log books are so important and we strongly encourage you to verify any data and calculations we discuss here with your own shooting experience.
The idea with the new method is that you do not want to be applying the cosine modifier to the actual range to the target but rather you want to be applying it to the total drop of your particular load at the straight line distance. So, instead of taking the .87 for the cosine modifier and multiplying it by the range, you want to multiply it by the TOTAL drop of your bullet at the straight line range to the target. For example, if you estimate the range to the target to be 530m, the M118LR would have a total drop (from the muzzle) of about 116″ in normal conditions. So, you would multiply that by the cosine modifier. If we were shooting at a 30 degree angle that cosine would be .87. So multiply 116 by .87 and you get 101″, or a change of about 15″. You would need to compensate by adjusting your point of impact 15″ lower on the target. This is the equivalent of the drop at about 500m, which is significantly different than the 459m you would come up with using the old method. This equates to roughly about a 20″ difference on target… that is a LOT!
With the new method, you need to insure that you are applying that value to the total drop at the straight line range to the target. The best thing to do is make up a chart for your log book for your particular load indicating the amount of adjustment you need to make at 100m increments with maybe 10 degree increments going down the other side of the chart. The chart the US Army used back in the day when I was doing this was actually in MOA adjustments, making it even a bit easier. Of course, if your scope is a MIL scope, make the chart in MIL adjustments. This new method is the current taught method in most sniper schools and is considered to be the more accurate method to use.
An Alternate Method
There is one other method that I have used and I thought I would mention here. That is the map/gps method. The concept behind this is actually the same as the old school way, you want to get the horizontal or X distance the bullet is going to travel. It so happens, that by using a map to estimate your ranges or even better, by using a GPS to tag points and then get the distance to them, it only gives you the X distance. There is no computation or math that you have to do. If you are operating in an AO and have the ability to go and tag points on your GPS in your AO, do it. Then you can use the GPS to report to you the distance from your current location to the tag points and then use that data on your range cards and elevation settings on your rifle. Obviously, you will suffer from the same inaccuracies as the old school method, but I have used this method a number of times at degrees of up to about 25° and it was fairly accurate. But the steeper the angle and longer the range, the more inaccurate the old school method, and this one, is.
Of course, the last method we have not mentioned is to use the angle compensating capability of your Laser Range Finder. This is quick, easy, and works very well. Different LRFs use different methods, so you would need to verify it for your particular rifle and load. The other downside is all of the other standard negatives that come with the use of LRFs. They will break, they will not work in rain, snow and heavy dust, the batteries will die, they will give away your position to anyone who happens to be utilizing night vision devices. etc. But they do work.
Hopefully our look into slope dope shooting has provided some helpful information and benefit. Like usual, the best way to figure it out is to get out there and test it and gain some experience. Until next time…shoot straight.
Mel – EIC
Sniper Central
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