Braxton Taylor
The maximum range a hunter can take an ethical shot on an animal is limited by a variety of factors, including the shooter’s skill, the stability of the rest, the ballistic capabilities of the cartridge, and the accuracy of the rifle.
If we’re being honest, it’s that first factor that limits most hunters, including yours truly. But that’s a topic for another day. Right now, I want to look more closely at an assumption that many hunters make, and it’s one that has, unfortunately, been repeated by gunwriters and forum warriors alike.
You’ve probably heard it. It doesn’t have a name, but I’ll call it “linear group size.” This is the idea that if your gun shoots one minute of angle (or about one inch) at 100 yards, it must shoot one MOA at longer distances as well (two inches at 200 yards, three inches at 300 yards, etc.). According to this theory, group size expands linearly as you extend a rifle’s range.
In the field, this translates to the expectation that I can put a bullet in an animal’s vital organs as far as that linear expansion will allow. If a whitetail has an eight-inch vital zone, and my gun shoots one MOA at 100 yards, I should be able to shoot a whitetail out to 800 yards as long as I have a stable rest and the bullet is carrying a reasonable amount of energy.
If you’re an experienced long-range shooter, you’re probably shaking your head. But you’d be surprised at how often this assumption gets thrown around. This comment on the Long Range Hunting Forum references the linear group size myth and says there’s a “definite perception” that it exists.
The replies do a good job explaining why the myth is incorrect, but I’m apparently not the only one who, as a novice rifle shooter, was shocked and appalled when my “one MOA gun” looked decidedly less like a one MOA gun the farther I ranged it out.
The Wind, Your Bullet, and You
If you’re still scratching your head, here’s why the linear group size assumption doesn’t translate to the real world.
First, with most hunting cartridges, shooting at 100 yards doesn’t give the wind enough opportunity to have its shot-busting impact. The wind can be whipping across at 10 or 15 mph, and you’re unlikely to notice much change in your point of impact at 100 yards. But extend that range to 300 or 400 yards, and those one-inch groups will quickly expand. I suppose if you had a perfectly consistent wind all the way out, the group size might remain the same. But the wind is never that consistent, so your groups won’t be, either.
Let’s put some numbers on that. If you’re shooting these 165-grain .308 Win. loads from Sig Sauer, the bullet will drift 3.5 inches at 300 yards with a 5 mph crosswind. But if that wind jumps up to 15 mph, that same bullet will drift over 10 inches–a 6.5-inch difference. At 500 yards, that difference is even greater: a 5mph wind moves the bullet 10 inches while a 15 mph wind shifts the point of impact over 31 inches. So much for your one-MOA groups.
A skilled long-range shooter can account for the wind by shifting the point of aim to the right or left. But no one can predict the future, and the wind can change in an instant. Even if your gun shoots a single, ragged hole at 100 yards, you can’t count on that same performance downrange.
This problem becomes even more pronounced with cartridges that can’t accommodate pointed, high-ballistic coefficient bullets (“ballistic coefficient” or “BC” describes how well a bullet can buck the wind). I’m thinking of snub-nosed cartridges like the .45-70 as well as slower cartridges like the .30-30 Win. The bullets fired from these cartridges slow down quickly, which makes them more susceptible to wind and less predictable in their flight.
To take a less scientific example than the one above, the 300 HAM’R rounds I tested in my review of the Wilson Combat NULA Model 20S dropped off significantly past 200 yards. The 300 HAM’R is a souped-up 30-30 Win. with low-BC .30-caliber bullets traveling about 2,500 feet-per-second (fps). The cartridge performed extremely well at 100 and 200 yards, posting one- and two-inch groups, respectively, at those distances.
If I was trusting the linear group size fallacy, I might expect three-inch groups at 300 yards. But when I reached that distance using the same bullet on the same day, the groups expanded to 5.5 inches. Still small enough for a vital shot on big game, but definitely not one MOA. Those low-BC bullets were losing serious velocity between 200 and 300 yards, which made the points of impact far less consistent.
Wind can throw off a shot, but so can inconsistent ammunition. Ammunition that produces extreme velocity swings from shot-to-shot can also result in high and low misses at longer ranges. That’s why long-range competitive shooters sometimes care more about their ammunition velocity’s “standard deviation” (the average distance away from the mean velocity) than they do about group sizes at 100 yards. They know that if their ammunition has a low SD, it will produce better results downrange than ammunition that shoots tight groups at 100 yards but has a high SD.
One final reason you may not be making consistent shots at longer distances is that your scope isn’t properly sighted in. I ran into this issue while prepping this Tikka T3X for the upcoming deer season. I wanted to have complete confidence in the rifle out to 300 yards, so I set up a paper target at that distance, dialed the scope, and shot a five-shot group.
Even though the rifle appeared to be sighted-in perfectly at 100 yards, my group at 300 yards was decidedly to the left by about four inches. I checked to make sure my scope was level in relation to the action and that it remained level during each shot. Still, the next groups were also veering off to the left. So, I adjusted my scope to get on-target at 300 yards. I expected my shots at 100 yards to skew to the right, but they remained on-target.
Your rifle might look sighted-in at 100 yards but actually be slightly off. You won’t know for sure until you shoot some paper at longer distances. If you plan on shooting an animal at those ranges, be sure to get rounds on paper and verify your zero. You’ll be glad you did when that buck is on the ground at 300 yards rather than running wounded, who knows how far away.
Last Shot
Wind and velocity fluctuations, combined with questionable scope zeros, are enough by themselves to turn a “one MOA gun” into something far less consistent at 300 or 400 yards. And that’s not even taking into account buck fever, unstable shooting rests, numb trigger fingers, and everything else that impacts the shooter rather than the gun.
How do you accommodate for all these variables to make an ethical shot? Practice, testing, and room for error. Practice can show you how your bullet responds to various wind speeds and directions. Testing can reveal fluctuations in ammunition velocity and real-world group sizes at longer ranges. Lastly, since results at the range rarely translate perfectly to the field, give yourself plenty of room for error before you pull the trigger on an animal.
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