You Probably Overestimate Your Lethality on Game
Last November I went on a mule deer hunt in Montana that was, for me, an experience of a lifetime in many ways. Thirteen days blocked off the calendar, with nine full days open to hunt, no cell service and a remote location. We put in 10-12 miles a day of rucking in and out of the woods at between 6,000 and 8,000 feet of elevation, just three friends and no professional guides…well, one of those friends is so good at hunting, we can put an asterisk on that!
The neighbor…that is for sure “guide” material.
In preparation for this, I broke the mold and added a caliber to my very tight consolidated portfolio of cartridges. I chose to go with 7PRC and I spent significant time at the range getting my cartridge performance data, my real world DOPE lined out and matching up the ballistics calculators in my binos as well as on my smart device.
The hunt proved to be successful as I made my longest shot to date on game at 654 yards. A single 175 grain Hornady ELD-X was sent out from my rifle mounted on a tripod and the buck never moved an inch. A lot of work went into make that one shot, but was it the correct one to take?
Subsequent long range sessions have raised awareness to more of the factors at play when making long range shots at game. There is much more to consider other than whether or not you, or your rifle can shoot well enough. In fact, in most cases that is likely not going to be your limiting factor. Most guns today are more than capable of the consistency required for these types of shots, at virtually any reasonable price range. Shooting education is more available, and better than ever.
However, when shooting at game, what is our standard for how consistent we must be in order to make an attempt on a living creature? When I was not even a teenager and my father was teaching me how to shoot a bow, I still remember to this day what his standard was:
“Son, when you can hit that paper plate 9/10 times at that distance, you can shoot a deer there.”
If you ask me today if that standard holds up, I would say yes, I would also say I believe that to be the minimum.
So you have your brand new rifle, your case of match (or reloaded) ammo, your Kestrel, your chronograph and you go out to gather DOPE for your chosen weapon system. You plop down at the range on a bipod, rear bag, either prone or seated and proceed to knock out some impressive groups. Armed with your DOPE and data, you believe you are ready for long range hunting, but the reality of the situation…the actual math behind the probabilities, has yet to speak.
The very first reality we must face is the difference between our ability to shoot consistently at the range versus the field. Besides the very obvious fact that in the field our nerves and heart rate are significantly heightened, reducing our ability to shoot consistently, we are also presented with less than ideal positions, support and weather. If you can shoot a 1” group off the bench with a rear bag and then are forced to shoot from the railing of a tree stand, off of a tripod, or just leaned against a limb in the woods, your group size will significantly grow in size. The good news is, this is easy to test, the bad news is you still haven’t factored in your nerves, moving game or the reduced time frame to make the shot.
For the sake of this article, we are going to assume in non-bench rest scenarios your group size will grow by 50%. Depending upon your level of skill, this will be larger or smaller. But it would not be uncommon for a 1” group shooter to grow to a 1.5” group shooter when moving to a standing tripod for support or shooting from a tree stand.
The second reality we must face is our ability to call wind speed, wind direction, target ranges or any other variable of our environment. For the most part, target ranges will be pretty spot on if you are using a rangefinder, but even if you do your part, those have tolerances as well. My very nice set has a tolerance of +/- 1 yard all the way out to 1640 yards, so this is likely not to be a factor provided I range the animal and not anything in front or behind it.
Wind calls however, are a matter of skill, and you need to be honest with yourself on how close you can call wind and direction. Having a Kestrel is nice and handy, and gives you a wonderful wind readout, but it can only read the wind and direction at where you are standing. Most of the time at the distances we are discussing that means the Kestrel wind read out is worth just a little more than nothing at all.
Your other environmental factors are also important, and something like a Kestrel will give you real time temp, humidity and station pressure, all that will affect your bullet flight. If you are using these tools, you are increasing your hit probability. If you are not, you will need to determine your ability to properly estimate these parameters and what the range of your estimation ability actually is.
The third reality is your ammo. While it may seem that your ability to print a half-inch group at 100 yards is all you need to know about your ammo, its actually only part of the equation. When you chrono your rifle you need to pay special attention to the standard deviation in your velocities. In simple terms without going too far into it, this the difference or variability in velocity versus your mean. As a simple example, if I have mean velocity of 2600 fps after firing 20 rounds and my standard deviation of that 20 rounds is 20 fps, that means roughly the following: Approximately 68% of my shots will chrono between 2580 and 2620 fps. Roughly 95% of my shots will chrono between 2560 and 2640 (double the SD) and roughly 99.7% will chrono between 2540 and 2660 fps (triple the SD).
This is a very important factor, because 20-60 fps variance is not likely to show up at all in your 100 yard group size, but significantly effects what happens down range. Here is a real world extreme 100 yard vs 1000 yard example of what the velocity variation in your ammo will look like at those two yardages:
Weapon System: 16” 6.5 Creedmoor, 143 grain ELD-X, 2520 fps mean, 20 fps SD, 0.291 G7 Ballistic Coefficient, 100y Zero
100y Shot:
Adjustment in inches @ 100 yards at 2520 (mean) fps = 0”
Adjustment in inches @ 100 yards at 2500 fps (1 SD, 68% of shots) = 0”
Adjustment in inches @ 100 yards at 2480 fps (2 SD, 95% of shots) = 0”
Adjustment in inches @ 100 yards at 2460 fps (3 SD, 99.7% of shots) = 0”
1000y shot:
Adjustment in inches @ 1000 yards at 2520 (mean) fps = 0”
Adjustment in inches @ 1000 yards at 2500 fps (1 SD, 68% of shots) = +7.2”
Adjustment in inches @ 1000 yards at 2480 fps (2 SD, 95% of shots) = +14.6”
Adjustment in inches @ 1000 yards at 2460 fps (3 SD, 99.7% of shots) = +22.18”
Now, here is the scary part. You must (roughly) DOUBLE those numbers, because we only accounted for the rounds that fell 1, 2 or 3 SD’s below our mean, we must also account for those that are above our mean. In the 3 SD (2460 fps) example, we would be need to come up 22.18” to match a round impacting at the 2520 fps mean. If we go the the other way to 2580 fps, we would need to go down 20.31” to match the impact of our mean round. So while it’s not exactly double, its close enough.
What does all this mean? Well, your gun is capable of 1” at 100 yards which would mean you are capable of a 10” group at 1000 yards with all else being consistent. But your ammo, carrying a SD of 20fps is only capable of producing a roughly 28” group at 1000 yards 95% of the time. The differences you can expect in velocity will yield this large cone of accuracy. I used the 95% example, because 1 SD (roughly 14” group), would only be 68% of the time and does not meet our standard of a 9 out of 10 probability.
Now, we had an extreme example, showing you how ammo SD makes little to no difference at 100 yards and a world of difference at 1000 yards, but where does the rubber really start to meet the road in terms of distance? Having run multiple numbers myself on various platforms and weapon systems, for most modern calibers and appropriate target sizes, I would say that distance is somewhere around 600 yards, under good shooting conditions where your avg group size would be at, or close to, bench rest consistent. Beyond 600 yards, the difference in your ammo’s velocity will really start to show up IF you can’t control for this.
What can you do about this? Well, you can buy/find ammo that has the lowest SD’s possible that also shoots good groups in your gun, or you can reload. From my experience, most Hornady match ammo will chrono at around 15 SD. Reloaders easily pull that number into the single digits and great reloaders can get below 5 SD…or better.
To help visualize and estimate/calculate your maximum effective range on game, there is a fairly simple and straightforward hit probability calculator located here from Blackburn Defense:
https://www.blackburndefense.com/tools/hit-probability
Simply input the target size you will need to hit, your group size, your muzzle velocity and its SD, the BC of your bullet, range, wind speed and direction. Note, the “Actual” columns are for what it actually is, the “Measured” columns is for what your predictions are and “Standard Dev” would be the range of your accuracy.
A good example is wind speed. You will enter what you estimate on your own, or what your kestrel told you. Then you will input the actual and your standard deviation would be the range of your consistency based upon your skill level. So if you think you can only accurately call wind within 3 mph, that will be your wind SD here. Once you input all the variables, you will get your hit rate. Continue to tweak the yardage until your hit probability is 90% or better. That is your maximum ethical range on a living target. Keep in mind, none of this really matters on steel or paper, or in instances where you can shoot multiple times. We are talking a single ethical round on a breathing animal. Big difference in your needed accountability level.
So, the question of the day is, should I have taken that 654 yard shot? Below is the results of that probability calculation using my numbers from my weapon system on that day:
654 yards, only yielded a 60.9 % chance a lethal shot would be executed on that day’s conditions
The sobering answer is NO. I used a 1.5” group size because while my gun is more capable than that, I was kneeling, in the snow, on a tripod shooting at an animal that had already moved 3 or 4 times just as I was about to squeeze the trigger. This was not a sub-moa situation for me considering the excitement and exhaustion of the moment.
Immediately following the successful shot. I am going to credit this one to the Lord.
We see here that the probability of me making a lethal single shot here was 60.9%, well below our 90% standard. I gave that muley buck a 14” vital circle, my velocity and SD is pulled from over 100 rounds of data and there wasn’t any wind to speak of during the time of shot, but we know, its almost never zero, so I gave my ability to call the wind a conservative 2mph SD on that day. In reality, my bullet landed precisely where I held on elevation, but I was roughly 6” right of my point of aim. I will admit, I completely blanked on my spin drift in the heat of the moment which accounted for a couple inches of that. Nevertheless, a perfectly lethal shot, and right at 1 MOA from my point of aim. However, when Monday morning quarterbacking, this was a shot that did not have a high enough hit probability for me to take.
If I wanted a 90% lethal hit probability, we need to keep backing up our shot distance until we find it, and on that day, in those conditions we needed to keep that buck inside of 475 yards.
My true maximum range for a 9/10 lethal probability under the conditions of that day: 475 yards
Trust me, the real hard part came AFTER this photo
There will be shooters that can significantly increase their maximum lethal range because they control for the variables much better, and there will be shooters that will have to drastically reduce that range. Keep in mind, we did not cover a complete and comprehensive list of factors here, so always lean on the conservative side. If you are a reloader with single digit SDs, capable of shooting 3/4” groups in field scenarios, your maximum range will expand. If you are unfamiliar with any of this, and don’t know your numbers, your lethal range will be much closer, likely in the 200-250 yard range.
The key is to be honest with yourself about your own capabilities in each scenario. If you are to respect the game you hunt, the life it lived and the food it provides, your goal should not be to see how far you can take game, but how high you can take your probability of success.
You have three ways to deal with improving your probabilities of success: You can either improve as a shooter, improve the consistency of your equipment or improve your ability to close yardage on the game you hunt. As for me, I plan on improving all three.
Proverbs 16: 32 - “He who is slow to anger is better than the mighty, and he who rules his spirit, than he who captures a city.”
“Pals”
