Registers – Calculators – Bar
Reexamination Certificate
1998-02-04
2001-03-06
Johnson, Stephen M. (Department: 3641)
Registers
Calculators
Bar
C033S277000, C042S107000
Reexamination Certificate
active
06196455
ABSTRACT:
BACKGROUND OF THE INVENTION
A portion of the disclosure of this patent document contains material which is subject to copyright protection. The owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.
1. Field of the Invention (Technical Field)
The present invention relates to an apparatus and method for determining in the field the range to target, and for adjusting the sight/aiming point to compensate for bullet drop or drift at that range, for a firearm, specifically for a firearm equipped with a telescopic sight having a mildot type of reticle.
2. Background Art
The mildot reticle is in increasingly widespread use by long-range rifle shooters as a means of estimating the range to the target. This estimation is critical in order to correct for the varying degree of projectile drop (and/or wind drift) at different ranges and thereby enable the shooter to hit the target. With training and familiarization, and by using the mildot reticle and then making the appropriate calculations, an experienced marksman can accurately estimate the range to target.
Initially incorporated into telescopic gun sights designed for military (and later police) use, the mildot reticle is the object of growing acceptance in the civilian sector among target shooters and hunters. By using a set of fixed dots within the telescopic sight, the shooter can compare the size of a target, a portion of the target, or a nearby reference target when viewed through the sight to the series of precisely sized and spaced dots on the reticle. On a mildot reticle, the dots are uniformly center-to-center spaced at 1 mil, which spacing appears to subtend a length of approximately 36 inches on a target viewed at 1000 yards. By estimating the size of the target or a reference near the target, and noting the number of mils that equal the size of the target, the shooter can apply a formula to calculate the range to target. This formula is simply expressed as: size of target in yards multiplied by 1000, and that product then divided by size of target in mils, equals range in yards. Currently, this calculation is performed in the field using a conventional hand-held calculator.
The present method of using a mildot reticle poses several serious challenges to the shooter. The necessary calculations are somewhat complex, and depend upon the shooter's ability to correctly remember and apply the formula. Dimensional analysis further complicates the process, as the size of the target more often than not is mentally estimated in inches, necessitating an additional calculation to convert the target size into a decimal equivalent of yards. The shooter generally must carry and use an electronic digital calculator, necessitating numerous data entry steps.
Even after the shooter has performed the range calculation procedure, the amount of the bullet drop (or wind drift) applicable to the known range must be applied to the sight picture to enable an accurate aim that will result in a hit on target. Either the telescopic sight must be mechanically adjusted, or the sighting point (the intersection of the cross hairs) “held over,” to correct the elevation (and/or windage) of the gun barrel to compensate for the effects of gravity and/or wind. Determining this compensation necessitates a second series of calculations to convert the needed amount of elevation or windage correction into a gun sight adjustment or hold-over figure for the known range and load.
Besides presenting many opportunities for arithmetic error, the correction calculations are time consuming, which may prove problematic in certain scenarios, such as military or law enforcement counter-sniping operations, timed competitive target-shooting events, or hunting situations.
A need remains, therefore, for a calculator apparatus which eliminates the multiple data entry steps and simplifies the calculation procedures for determining range to target and/or elevation adjustment to compensate for bullet drop or drift over the range determined. The present invention was developed to satisfy this previously unmet need.
SUMMARY OF THE INVENTION (DISCLOSURE OF THE INVENTION)
The present invention relates to an analog calculator apparatus and method incorporating two rule members, slidably connected together and bearing logarithmic and inverse logarithmic scales, configured and controllably movable specifically to perform the following operations: (1) rapid and simple calculation of range to target, based on a measurement of the target with a mildot reticle, by aligning the estimated target dimension value on one scale directly opposite the mildot value on a second scale, and then reading from a third scale the range to target value aligned with an index mark; and (2) rapid and simple calculation of the amount of gunsight correction necessary to compensate for bullet drop and/or wind drift for a given distance to target, enabling the user to determine either the equivalent telescopic sight adjustment (minute-of-angle) or the equivalent hold-over (mils), by aligning an index with a range value on one scale, and reading an elevation compensation value in both minute-of-angle and mils, on a second scale directly opposite a bullet drop value on a third scale.
In accordance with the invention, there is provided an apparatus, useable with a telescopic sight having a mildot reticle, for determining the distance to a target of a known dimension. In one embodiment, the apparatus comprises: a first rule member; a second rule member controllably moveable adjacent to the first rule member; a mildot scale, comprising mil value marks, on the first rule member; a range scale, comprising range value marks, on the first rule member; at least one index point on the second rule member proximate to the range scale; and a target dimension scale, comprising dimension value marks, on the second rule member substantially parallel to the mildot scale. The preferred embodiment is used by controllably moving the second rule member to align a dimension value mark corresponding to the known dimension with a selected mil value mark on the mildot scale, with the result that one of the at least one index points is substantially aligned with a range value mark corresponding to the distance to the target. Preferably, the first rule member comprises an oblong rectilinear shape defining a rectangular aperture therethrough, and the aperture is disposed parallel between the mildot scale and the range scale. In the preferred embodiment, the second rule member comprises an oblong rectilinear shape movably disposed through slots in the first rule member, so that the second rule member is controllably movable axially within the aperture parallel to the first rule member. Preferably, a mildot reticle facsimile is provided on the first rule member parallel to the mildot scale. Also, optionally, means are disposed on the first rule member for determining a range correction factor for vertically angled shots.
The foregoing described embodiment is useful for determining range to target. Thus, according to the invention also is provided an apparatus, useable with a firearm having a known bullet drop over a known distance, for determining an adjustment to firearm elevation to compensate for bullet drop. The apparatus preferably comprises: a first rule member; a second rule member controllably moveable adjacent to the first rule member; a range scale, comprising range value marks, on the first rule member; at least one elevation scale, comprising elevation value marks, on the first rule member; at least one index point on the second rule member proximate to the range scale; and a bullet drop scale, comprising drop value marks, on the second rule member substantially parallel to the at least one elevation scale. Preferably, in use the second rule member is controllably moved to align one of the at least one index point with a selected range value mark
Baker Rod D.
Johnson Stephen M.
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