Those that shot precision rifle matches with me know that I do well in moving target matches. I'm often asked about the techniques I use (tracking vs. trapping, etc...) and one of the question that always comes up is how much do I lead the targets? To which I give an answer that is an angular value in mils. People are usually expecting my answer to be in inches, so this typically leads to another question about how much I adjust for different target speeds and different distances. When I reply that I only adjust for speed, that distance doesn't matter, this usually causes some confusion and disbelief.
It doesn't make any real difference in a match that is shot at known distance with a target that always moves at the same speed, but it does make a difference in real world applications, and I like doing things in ways that are usable off the range. So, I've created a few charts to try and illustrate how this works, and to maybe shed some light on one of the reasons why there is a big push towards first focal plane in tactical scopes.
Here is a charts that show the required target lead in inches for you typical 308 175 SMK load:
It's what you would expect: the faster the target is going and the further away it is, the more lead is needed. The movers carried on stick in Canadian matches are typically going at 1-1.5 MPH. Mechanical movers down in the US are usually between 2-6 MPH.
Here what it looks like if you convert those leads to mils:
Notice that for a given target speed, the lead in mils stays almost constant over a large distance. That is something that can be taken advantages of.
The thing you need to realize is that since it is an angle, differences in value make less of a difference at closer distances than they do at longer ones. So, if you wanted to use a single lead value for a particular target speed over a large distance, it makes sense to choose one from one of the farther distances.
Lets say we used the following values for different target speeds over the the entire 100-500 yard range:
If we predicted the target speed accurately and did our tracking or trapping properly, we would get the following errors:
These are pretty small, and if everything else was done correctly (wind call, hold, etc...) and the load was accurate, they would result in a hit. This works for any caliber, and the shorter the flight time of the bullet, the less error there will be and the larger the range of distance this will work over.
This is what the 6mm Crusader that I have been shooting this summer looks like:
Leads in inches:
Lead in mils:
Lead table that I use over distance, and the resulting errors:
Note that there is less error than the 308 load because of the reduced flight time.
Now, target speed is like wind: the best you can ever do is estimate it, fire a shot and make corrections (if possible). It is going to be an estimate regardless of which way you lead. The advantage to using the angular lead method is that your solution table looks like this:
versus this:
Its one dimensional vs two and is far easier to memorize and use since you only need to consider one thing: target speed. With a good reticle it can be done accurately, and in an FFP scope, you can do it at any magnification.
The other advantage is that you're focusing on the part of the target that you want to hit and not some space out in front of it. This typically helps with vertical deviation and you can often catch your own swirl and splash (if you use a break). The size of your target doesn't matter either. If your linear hold-off is not with respect to the desired point of impact, but rather to the edge of the target, another error is introduce if your target can vary in size or orientation.
It doesn't make any real difference in a match that is shot at known distance with a target that always moves at the same speed, but it does make a difference in real world applications, and I like doing things in ways that are usable off the range. So, I've created a few charts to try and illustrate how this works, and to maybe shed some light on one of the reasons why there is a big push towards first focal plane in tactical scopes.
Here is a charts that show the required target lead in inches for you typical 308 175 SMK load:
It's what you would expect: the faster the target is going and the further away it is, the more lead is needed. The movers carried on stick in Canadian matches are typically going at 1-1.5 MPH. Mechanical movers down in the US are usually between 2-6 MPH.
Here what it looks like if you convert those leads to mils:
Notice that for a given target speed, the lead in mils stays almost constant over a large distance. That is something that can be taken advantages of.
The thing you need to realize is that since it is an angle, differences in value make less of a difference at closer distances than they do at longer ones. So, if you wanted to use a single lead value for a particular target speed over a large distance, it makes sense to choose one from one of the farther distances.
Lets say we used the following values for different target speeds over the the entire 100-500 yard range:
If we predicted the target speed accurately and did our tracking or trapping properly, we would get the following errors:
These are pretty small, and if everything else was done correctly (wind call, hold, etc...) and the load was accurate, they would result in a hit. This works for any caliber, and the shorter the flight time of the bullet, the less error there will be and the larger the range of distance this will work over.
This is what the 6mm Crusader that I have been shooting this summer looks like:
Leads in inches:
Lead in mils:
Lead table that I use over distance, and the resulting errors:
Note that there is less error than the 308 load because of the reduced flight time.
Now, target speed is like wind: the best you can ever do is estimate it, fire a shot and make corrections (if possible). It is going to be an estimate regardless of which way you lead. The advantage to using the angular lead method is that your solution table looks like this:
versus this:
Its one dimensional vs two and is far easier to memorize and use since you only need to consider one thing: target speed. With a good reticle it can be done accurately, and in an FFP scope, you can do it at any magnification.
The other advantage is that you're focusing on the part of the target that you want to hit and not some space out in front of it. This typically helps with vertical deviation and you can often catch your own swirl and splash (if you use a break). The size of your target doesn't matter either. If your linear hold-off is not with respect to the desired point of impact, but rather to the edge of the target, another error is introduce if your target can vary in size or orientation.
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