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marksmanship and mechanical precision - larvatus prodeo
August 5th, 2008
01:21 pm

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marksmanship and mechanical precision
Observe yourself shooting a handgun. Mechanical accuracy of your firearm is defined as its intrinsic capacity to deliver bullets to the point of aim, irrespectively of all human factors. It is characterized by the figure described in the target plane by bullets it throws downrange, with its frame rigidly fixed in a machine rest. Likewise, your physiological capacity to hold and aim the handgun is characterized by the figure described in the target plane by your actual point of aim found at the intersection of the sight line with the target plane, deviating from your intended point of aim. Let us assume that your handgun is sighted in for consistent ballistic performance of your ammunition at the range equal to your distance from the target. That is, under these circumstances, the statistically average point of impact will coincide with the point of aim. With a centerfire pistol fired at short ranges, wind drift is a negligible factor. Accordingly, once the bullet leaves the barrel of your handgun, its point of impact will have been determined. As the shooter, you are in control of this determination, to the extent of your accuracy of aim and consistency of trigger letoff and follow-through. We shall consider radial deviation of the bullet’s impact in the target plane, conventionally designated by the hour mark in a clock dial. Let us neglect the effect of gravity and the likelihood and aptness of your muscular compensation therefor. Thus we assume for the sake of simplifying our analysis, that you are equally likely to deviate from your intended point of aim radially in any given direction. To this extent, your physiological capacity to hold and aim the handgun becomes circumscribed by a circle projected into the target plane by its sight line. Likewise, we assume that the point of bullet impact in the target plane is equally likely to deviate from the actual point of aim radially in any given direction. To this extent, the mechanical accuracy of your handgun is circumscribed by another circle, defined by the parabolic trajectory of your bullets, as it intersects the target plane. In this way, the arc of the gun superimposes upon the arc of the shooter. In other words, the mechanical looseness built into your handgun in order to ensure its reliable operation, compounds your errors of aiming, shooting, and following through. It does so regardless of the ratio of looseness to error. This compounding of error occurs as the center of the circle defined by mechanical dispersion ranges inside the circle defined by your capacity to hold and aim.

Heinrich Keller of Frauenfeld, Switzerland, aged 40, representing his country with a specially constructed 170mm-barreled W+F 1906/29 7.65mm Luger in his first international event, the 1949 ISSF competition in Buenos Aires.

Compounding of shooting errors becomes minimized in the hands of a good shot firing an accurate handgun. On the other hand, a shaky shooter given to habitual deviation from his target cannot reap much of a benefit from increased precision of his firearm. Generally speaking, the human factor counts for more than mechanical looseness in missing your target. For a careless shooter, shot dispersion stemming from his error tends to exceed its dispersion owed to the mechanical looseness of his gun. But aside from that, there is no sense in the notion of not needing a gun that shoots better than oneself. Even the beginner will visibly benefit from choosing a more accurate arm.

The original target of Keller’s fourth pass in the ISSF championship shows a perfect score of 100. It caused a sensation during that event, for no other shooter had managed such a result thus far. His overall performance in competition resulted in 10-shot targets that scored 96, 88, 95, 100, 88, and 92 points, adding up to the same 559 points that he had scored in preliminary training, achieving in each instance the best result of any shooter. Keller’s skill earned his 1949 ISSF title of World Champion in the 25m center-fire pistol event.

In the end, it is as likely as not, that all variations in the accuracy of your aim and consistency of trigger letoff and follow-through, within a given string of shots, will stack up in your favor. Statistically, this stroke of luck will arrive exactly as often as the occasions whereupon all of these variations stack up against you. With your personal best groups and your personal worst bookending the Bell curve, any single test target fired offhand will most likely fall the middle of the distribution. Its deviation from your personal average might be attributable to your mental or physical condition of the moment. But let us suppose that you could constrain these parameters. You might be able to do so by collating such deviations with self-reported or physiologically assessed evaluations of your fitness to shoot. Then the remaining differences would be due to subjectively inexplicable and objectively unpredictable variations of brute luck. In other words, pointing out a few targets shot offhand tighter than they come out of a machine rest day in and day out, proves little about the intrinsic precision of your gun or your skill as a shooter. The real mark of your skill is consistent achievement of offhand shooting scores that lie within the limits of mechanical accuracy of your gun.

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From:furia_krucha
Date:August 6th, 2008 09:25 am (UTC)
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Let us neglect the effect of gravity and the likelihood and aptness of your muscular compensation therefor. Then, to the extent that you are equally likely to deviate from your intended point of aim in any given direction, your physiological capacity to hold and aim the handgun becomes circumscribed by a circle projected into the target plane by its sight line.
Даже и без учета гравитации получится не окружность, а эллипс, т.к. стабилизация по рысканию и по тангажу обеспечивается разными группами мускулов.
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From:larvatus
Date:August 6th, 2008 09:40 am (UTC)
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“Consider a spherical cow…”
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