Conditions:
You wish to shoot a whitetail deer trotting at a consistent speed of 12 mph at 90 degrees to your line of sight. You are using a rifle chambered for 308 Winchester and shooting a load suitable for the purpose, in this case the Federal 180 grain Trophy Bonded Tip with a muzzle velocity of 2465 feet per second. (Fact: The correct answer to the question does not depend on minor differences in cartridge, load, or animal speed.)

Without looking it up, true or false:
If you are able to establish and hold a consistent lead on the deer, the lead required in minutes of angle or milliradians (angular measurements, not absolute inches or feet) will be approximately the same at ranges from 50 to 300 yards. For example, if the lead required is 26 MOA at 150 yards, using that same lead (26 MOA) when the deer is at any distance from 50 to 300 yards from the shooter will not change the point of impact on the game animal by more than 3 inches.

(All this assumes that everything else is accurate and consistent except as indicated, and that the shooter has a scopesight reticle calibrated in minutes of angle and which permits achieving and holding a consistent lead. In addition, this is just about leading a moving target, not any other ballistic differences such as the normal shot dispersion at different distances; assume the bullet goes exactly where the gun is aimed. It’s also not about whether you would take such a shot, whether you could accurately judge the deer’s speed or distance, if it’s an ethical hunting practice, etc. It’s just about ballistics.)

Answer true if you agree, but false if you believe the lead in minutes of angle or mils would vary much more than a specific average at different ranges up to 300 yards.
(Correct answer to be posted in the future.)

I've reset the poll to change the title.
At that point there were 9 (53%) true votes, and 8 (47%) false votes.

Question:
True or False?
.

Choices:
True
False

 

This message has been edited. Last edited by: sigfreund,

You are supposed to say “Myaaaa!”. The deer will stop and look at you. No lead required.

When I first read this question my instinct was to answer True...but then started to consider the distance (radius) increasing which would increase the lateral distance (linear distance) the deer crossed at the same given speed would therefore take longer to traverse. Lastly, I think I got hung up on semantics in deciding whether the difference fit "specific average". I decided to sleep on the problem and this morning decided to go with my first instinct and answer True.

Sigfreund, I want you to know that you cost me some sleep last night with this question...and I'm ok with that.

Looking forward to the explanation for the correct answer!

I voted false, but I'm not sure I really understand the question correctly.

Tony.

I've shot a fair amount of moving steel & paper targets, in training & competition, at distances from 70 to 800 yards, using 223/264/308 bores. I'm pretty comfy with the required leads, but won't comment yet.

It was difficult to word the question so it would be clear, and I feared that I had not been completely successful.

Hopefully everything will become clear later when I explain the right answer.
I will edit the topic title when I do that so it's not necessary to open the thread to check.

double distance, half the lead, inverse proportionality.

I would use at least 158 grains of lead.

Okay, before everyone has to go to work tomorrow (and people can’t get to sleep tonight), here’s the answer and explanation.

First, it’s true that the angular (not absolute) lead remains very close to the same average value for all distances from 50 to 300 yards in this instance. This table is based on the load described above under “standard” atmospheric conditions, but similar results will be obtained for other loads and conditions. All that’s necessary to prove it is to use a ballistics calculator like the JBM.

Calculate a table using all the appropriate data and then look at the far right “lead” column in minutes of angle or milliradians. We see that the figures don’t change very much until longer distances as the bullet loses velocity. Using an average or median lead figure as the lead for all the distances, especially over a reasonably short range of distances, will usually keep the bullets within a small range as well.

Formatting in these posts isn’t something I’ve mastered, so forgive uneven columns.

Range (yards) / lead, actual inches / actual MOA lead / lead in inches for 26 MOA
50: 13.1 / 25.0 / 13.1
100: 26.7 / 25.5 / 26.7
200: 55.3 / 26.4 / 54.4
250: 70.4 / 26.9 / 68.1
300: 86.4 / 27.5 / 81.7

I realize the above table is difficult to follow, and I provide it just for full info, but let’s look at the specifics.

At 50 yards the actual MOA lead is 25.0 MOA, or 13.1 inches. Using 26 MOA at that distance gives us a calculated lead of 13.1 inches, or the same (due to rounding).

At 100 yards the actual MOA lead is 25.5 MOA, or 26.7 inches. Using 26 MOA at that distance gives us a calculated lead of 26.7 inches, or the same (due to rounding).

At 200 yards the actual MOA lead is 26.4 MOA, or 55.3 inches. Using 26 MOA at that distance gives us a calculated lead of 54.4 inches, or only 0.9 inch difference from the actual lead.

At 250 yards the actual MOA lead is 26.9 MOA, or 70.4 inches. Using 26 MOA at that distance gives us a calculated lead of 68.1 inches, or 2.3 inch difference from the actual lead.

At 300 yards the actual MOA lead is 27.5 MOA, or 86.4 inches. Using 26 MOA at that distance gives us a calculated lead of 81.7 inches, or 4.7 inches difference from the actual lead. (Note that I made a mistake in this last earlier and corrected it now. It does fall outside the 3 inches I mentioned above, but still within a deer’s vital zone.)

What this demonstrates is that although the actual absolute lead in inches that’s required increases dramatically for each increase in distance, the lead in angular minutes of angle remains very close to the same. In this example, “very close” means that using an average for the MOA lead (26 MOA this time) yields values that are very similar to the actual absolute lead figures. Or in other words, if a hunter were to lead the deer by the same 26 MOA for any shot from 50 to 300 yards, he would hit very close to the same spot every time (subject to the conditions in the original post, of course).

All of the same applies if we’re using a reticle calibrated in milliradians and a lead in mils. In this example a lead of about 7.5 mils would give us similar results to using 26 MOA, but not exactly because 26 MOA = 7.56 mils.

Clear as muddy water?

Lead on moving targets is shown in ballistics programs such as JBM. The lead angles are highly dependent on bullet velocity, less so on distance to target.

For many calibers used in competition, lead on movers can be approximated by using 2 MOA per mile per hour of mover. Thus, 12 mph translates to 24 MOA lead. Not exact, but with a little faster caliber, the general rule is close enough for most of the movers and distances we encounter in precision/tactical competition.