Minute of angle myth.
About the only form of hunting that eables us to take advantage of virtually all the accuracy of wich our rifle/ammo/scope combination is capable is varminting. I'm talking 'chucks ("marmots" in the west), crows, and prairie dogs primarily--the kinds of hunting that allow you to set up what in fact is a ground-level shooting bench complete with bipod and sandbags. A typical shot is taken under conditions which have us perfectly relaxed as to breathing rate, if not heart beat; conditions which enable us to use virtually all the accuracy a rifle can delivery, even if it's a mythical one-holer.
But let's be realistic. Let's assume a half-minute heavy-barreled varmint rifle with the machine-rest capability of shooting 1/2-inch groups at 100 yards, 1 inch at 200, etc. Say our rifle is a 22-250 with a 12X fixed power scope. Our 55-grain spitzer bullet exits at 3,800 feet per second (fps) and is zeroed to print dead on at 200 yards. Given those figures, we'd be 4.5 inches low at 300 yards, and 12.9 inches low at 400. Our "point-blank range" (PBR), that distance within which we can aim directly at our target without though to trajectory and still hit, varies with the size of the target.
Assuming a large chuck or marmot sitting up so as to give us the largest vertically-oriented area, we're looking at a PBR of about 375 yards, assuming a typical chest hold. If the rodent's down on all fours that reduces our target from about 12 inches to less than 6; subsequently, our BPR is reduced to about 275 yards. On a perched crow whose deceptively small, egg-shaped body measures about 4 by 6 inches, our PBR is reduced to around 230 yards.
We could, of course, use a 300-yard zero, as many varmint shooters do, but in so doing our bullet is about 4 inches high at the 175-yard mark, and without hold-under we'd over-shoot a crow or down a 'chuck. On the other hand, a 300-yard zero would put us just under 8 inches low at 400 yards so if' chucks or marmots at consistently long ranges are the primary target, the longer zero would give us a PBR of about 425 yards if we ignore smaller stuff at moderate ranges. And of course a 30-yard zero would be mandatory for those shooting at little critters 500 yards away or more. After all, with a theoretical accuracy of our half-minute rifle delivering 2-1/2-inch groups at 500 yards, we'd have the capability of hitting at that range, right?
At this point it's tiem to throw a liberal amount of reality into the equation in the forms of sighting error, steadiness of hold, range estimation, wind, and mirage. In the typical, fine-wire crosshair of a 12X or even a 16 X varmint scope our reticle subtension averages about an inch at 500 yards. To that we can add a couple more inches for pure sighting error alone (have you ever looked through a scope at a target an honest 500 yards away?) Unless the scope is absolutely parallax free, which is highly unlikely, these factors all combine to at least double the radial dispersion of our groups, i.e., 2-1/2 inches of aiming error or 5 MOA.
Bear in mind now that we're assuming an absolutely perfect rest, no wind, no mirage and our knowing that the target is exactly 500 yards away. I don't know about you, but just about every place I've hunted chucks and prairie dogs over the past 25 year there's been lot of wind, plus mirage.
The amount of apparent mirage varies with the intensity and angle of the sun, plus the temperatures of the air and ground. Again, if you've ever looked through a relatively high magnification scope over 500 yards of sun-baked pasture or prairie, you can't imagine how difficult it can be just to make out the target, let alone know where to hold; it's like looking at ghosts through the flames of a fire. Many times I've seen mirage conditions so bad that 250-yard shots become iffy.
Benchrest shooters are supposed to be able to "read" mirage and compensate for it to a degree on their 100 to 200-yard courses but in really long-range field shooting I've yet to understand what it is they'd be reading. All I see is a vague, amorphous form which appears to be dancing on fire and under water all at the same time. Over the years I've punched holes in beaucoups of 'chucks and prairie dogs--like several thousand, and I can't tell you any more about "reading" mirage other than to tell you that it's much less of a problem on cloudy days and during the first and last 2 hours of the day. Period.
As "guessy" as mirage-reading is, it's almost a scientific discipline compared to estimating range and wind deflection. Of the two, the former gets most of the ink in discussions such as this, but the effect of wind on a bullet is at least as important to a hunter, probably more so. Let's now look at how each affects our ability to place a bullet accurately out at extreme range.
Let's again use our highly-accurate .22-250 and assume a dead-steady sandbag rest, no mirage problems whatsoever, and our 12-inch high woodchuck sitting dutifully at precisely 500 yards away. And, for the sake of simplicity, let's assume we're zeroed at 500 yds. so no holdover is necessary.
As we peer through our 12X scope and start to tighten on the trigger we fail to notice the slight breeze against our cheek and the ripples moving over the grass in front of us. It's the kind of wind that doesn't even get our attention ... say, a 5 mile per hour (mph) zephyr.
Everything looks perfect. We squeeze off. The 'chuck is amused. Our 55-grain pill has passed 12-1/2 inches to the side. In a 2-1/2 mph crosswind--one so slight as to be hardly noticeable--we'd have been 6-1/4 inches off target. Still a clean miss.
Can you tell the difference between a 2-1/2 and a 5 mph wind? Or a 5 mph wind from a 10 mph one? If you're going to shoot at little critters 500 yards away you had better; that 10 mph breeze will put you more than 25 inches off target. Even if we could precisely judge wind, it never blows consistently and at the same velocity over large areas. Next time you're out, pay close attention to the grass movement over a 500-yard distance; you'll see some areas where there's little or no movement while in others the grass may be swaying briskly.
Even if we had a "textbook" wind blowing say, 10 mph from left to right, we'd have to hold 22 inches from the left edge of our sitting woodchuck. If we misjudged that hold by more than 3 inches either way, i.e., held less than 19 or more than 25 inches into the wind, we'd miss our 6 inch-wide target.
In my experience I've found a natural reluctance among hunters to actually believe that wind, even modest amounts of it, can cause a bullet to drift so far off target. A bullet's dropping due to gravity is a much easier concept to handle. Once we learn that even the lightest bullets from our flattest-shooting magnums start dropping rather drastically out beyond 100 yards, the idea of holding over to compensate on long shots is logical. But holding a foot or two off to the side is not so easily accepted, especially when in a game hunting situation where a particularly coveted trophy may be at stake.
Equally important to critical bullet placement at long range is our ability to estimate distance with a fair degree of accuracy. To understand why it's so important we must again look at the trajectory of our supposedly string-flat .22-250 cartridge. The actual bullet drop for our 55-grain slug exiting at 3,800 feet per second (fps) is about 46 inches below the boreline at 500 yards. By mounting a scope 1.5 inches above the bore and angling it downwards to intersect the bullet's path at some distance downrange, we're actually dividing the bullet's are above and below the line of sight and thereby extending the PBR.
Zeroed at 300 yards, then, our bullet path relative to the crosshair would be almost 4 inches high at around 170 yards; 7.9 inches low at 400, and 22 inches low at 500. Still shooting at our extremely patient 5-inch wide, 12-inch high groundhog, we find that if we can somehow hold precisely 22 inches above its chest (a task which in itself is subject to several inches of sighting error), we would shoot under our varmint if he were at an actual 540 yards. That figure is based on our 55-grain slug dropping 22 more inches below the crosshair between the 500 and 600 yard marks and using a chest hold approximately 8 inches off the ground. If the 'chuck were down on all fours, our smaller, 5-inch high target would be missed clean if we misjudged the range by 25 yards.
Now, have you any idea what the chances are of estimating to within even 100 yards of an object at a true 500 yard distance over unfamiliar ground? According to U.S. Army tests, for artillery observers trained in range estimation, the very best they could expect was plus-or-minus 100 yards at 500. A really good, experienced varmint hunter could be expected to do just about as well on ground he's never seen before.
I stress the unfamiliar ground aspect because that's an extremely important factor. Most varminters hunt familiar fields year after year so they know distances to various points within those fields. It's the same with prairie dog shooters; they set up and shoot from the same spot so even if they don't pace off distances, continued shooting eventually gives them a good idea as to the proper hold for various ranges.
We've thus far spent all out time talking about the most precise form of hunting, varminting, to make the following point: Give a super-accurate rifle, a high power scope and a dead-steady rest, hitting on the first shot even an object as large as this 8-1/2 x 11 inch piece of paper you're reading at 500 yards is a mighty tall order under ideal circumstances. Throw in a little wind- ... or mirage ... or both, plus our natural inability to judge distances, and it becomes an even taller one.
Now let's look at today's typical biggame rifle and see what limitations are placed on its potential by the realities of hunting. As typifying our modern musket let's use a bolt-action sporter in 7mm Remington Magnum wearing a 3-9X variable scope. The load we will use is the 150-grain spitzer at 3,100 fps. Using a 200-yard zero, we are looking at a 6-inch hold-over at 300 yards; 18 inches at 400 yards, and a full 36 inches at 500 yards.
As for theoretical accuracy, let's assume we've got one of those minute-of-angle gems we hear talked about so frequently but in truth are quite uncommon. But let's say we have one anyway; a rifle capable of producing 1-inch, five-shot groups three out of four times at 100 yards (my own criteria for an MOA rifle). And we'll again use the unrealistic range of 500 yards at which we'll say the machine rest capability of our rifle will be 5 inch groups or 2-1/2 inches of dispersion on any given shot.
Enter reality. Given our typical variable scope set at 9X, let's be generous as hell and add only another 1-1/2 inches of dispersion for sighting error. We now have an 8-inch group from benchrest at 500 yards.
Now let's throw away the shooting bench, tripod and sandbags. Under the most ideal hunting conditions imaginable the best we can hope for is to be physically rested, i.e., not breathing heavily from a run or climb, and to be able to shoot from a prone position with some sort of makeshift field rest that gives us a two-point support--a rock, log or hat under the forearm and the toe of the butt on the ground. I've shot many, many animals under the aforementioned conditions so they are not the rare...but not at 500 yards. In fact, as we shall see, after we throw in a few more factors that will further limit our shot placement ability, that two-point rest and prone position become mandatory if we reasonably expect to make even a 300-yard shot on a game animal.
Mountain and open plains hunting lend themselves better to prone shooting then brush and forest hunting. The eastern whitetail or black bear hunter almost never gets more than a tree to lean the fore-end against, and he's lucky if he gets that.
Now let's return for a moment to the gent in the prone position with a good, two-point rest. Upon sighting game this guy may have been posted the entire afternoon so his breathing and pulse rate would have been normal. But once our nimrod spots an animal he wants to pull the trigger on, I guarantee you his breathing will become much heavier and the pulse rate will nearly double...just getting into a prone position and lying there! No amount of experience or individual psyche is going to substantially alter that effect. If it did, I would personally recommend that fellow look for another and more exciting hobby...like mine field gardening or shark dentistry.
We can expect that just by throwing in a little excitement, a slightly less-than-perfect rest, and normal sighting error, our 5-inch 500-yard group is now 10 inches minimum (5 inch dispersion). And believe me, I'm being optimistic in the extreme as well as allowing absolutely ideal conditions: no wind, no mirage, no physical exertion, a near benchrest support, and the knowledge that the target is exactly 500 yards away.
Take away that two-point support and prone position and substitute the next steadiest field position-sitting and with a tree or boulder against or on which to support the fore-end, and we're lucky if we can put five shots into 25 inches at 500 yards. Throw in a typical range estimation error of plus or minus 100 yards (if you're very good at it), and our group gets larger yet.
Then there's the wind, let's say a 10 mph job, which is a mere zephyr on the western Pronghorn plains. Given that, there's 17 inches of deflection it imparts to our 150-grain bullet that must be compensated for.
And last but not least, let's toss in a little physical exertion; after all, a relatively small percentage of game is shot without some running or climbing immediately beforehand so that we're often forced to shoot with chest heaving and pulse racing. I once tried to brain-shoot an elephant at 30 yards after running up a small hill in 110-degree heat. I could barely breathe, much less hold a rifle steady enough to hit a football-size target at 30 paces. I missed the brain four times.
Unfortunately, the one shooting position forced upon us the most frequently is also the unsteadiest: standing and offhand. If you're an fair-to-middlin' shot and practice a bit year 'round, chances are you can put 10 shots into a dinner plate at 100 yards--say a ten-inch group. That's of course assuming our MOA rifle and you being at normal pulse and breathing. Now, pace off 100 yards from your shooting position, sprint back to your rifle and take another offhand shot at that 100-yard target. I'll even give you 30 seconds to settle down before shooting--something the game will rarely do. Do that five times and see what kind of group you can shoot.
The message is clear: when it comes to accuracy we need all we can get because it's the one constant over which we have some degree of control. Another message should also have filtered through: that 500 yards is far too great a distance to even contemplate shooting at game, even with a benchrested MOA rifle under the very best of circumstances--the kind that never occur in the game fields.A Indeed, once we throw in the certainties: the accelerated pulse and breathing rate; the sheer guessing as to wind velocity and target distance and how it should affect out hold, placing the first shot in the vital area of a deer-sized or larger animal at 300 yards is quite an accomplishment from the prone position and a steady rest. From any other position it's not only wishful thinking, but disrespectful of the game and unworthy of a sportsman.
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|Author:||Sundra, Jon R.|
|Publication:||Guns & Ammo|
|Date:||Sep 1, 1984|
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