Abstract:
An adjustable iron sight for firearms includes compensation for projectile drop. The projectile drop compensation moves the sight aperture to compensate for projectile drop. Use of the compensation will allow aiming directly at the target without having to visually compensate for projectile drop. The projectile drop compensation mechanism includes a multi-position manually operable wheel and cam that is profiled to match the trajectory of the particular firearm and load. As there are many possible loads that could be used with a particular firearm, the multi-position cam is interchangeable to allow changing to a cam that is matched to the specific load that is desired.

Description:
[0001]    In general, the present invention relates to firearms and particularly, the present invention relates to an adjustable rear iron sight for firearms including height adjustment compensation for projectile drop. 
       BACKGROUND OF THE INVENTION 
       [0002]    Virtually all firearms are equipped with some type of sighting system to facilitate aiming the weapon. Examples of these sighting systems include telescopic sights, holographic sights, laser sights and iron sights. Iron sights also called open sights, consist of a front sight and a rear sight that the shooter aligns together onto the target he/she is aiming at. Iron sights can be either fixed or adjustable and made from iron or any other material 
         [0003]    Adjustable iron sights allow for vertical adjustment called elevation and horizontal adjustment called windage. In use the sight is adjusted so that projectiles fired from the firearm will hit the target at the same point that is seen by aligning the sights to the target. This distance from the firearm to the target is known as the zero range. At distances in front of the zero range the projectile will hit the target above the line of sight and at distances beyond the zero range the projectile will hit the target below the line of sight, due of course the projectile drop caused by gravity and changes in velocity. 
         [0004]    Typically firearms use an adjustable rear iron sight to compensate for projectile drop and these often use a fine adjustment screw for accurate adjustment. However the fine threads of the vertical adjustment screw often required multiple complete and partial turns to get to the correct setting, with the likelihood of making a mistake in counting that would result in an incorrect setting and also losing the initial zero range setting. Even when the sights have markings these are often difficult to read and generic, that is they require knowledge of the trajectory of the firearm/load combination in order to adjust the single elevation screw to the correct setting. 
         [0005]    Some military iron sights from the prior art allow for projectile drop compensation but only for a standardized military load. The increments of elevation are also too large to be useful for hunting. 
       SUMMARY OF THE INVENTION 
       [0006]    It is one object of the invention to provide an improved adjustable rear iron sight for a fire arm. 
         [0007]    According to one aspect of the invention there is provided an adjustable rear iron sight for a firearm comprising: 
         [0008]    a rear sighting element for mounting at a rear of the fire arm and defining a visible alignment portion for visual alignment by the user with a front sighting element; 
         [0009]    a mounting member having mounting elements for attachment of the mounting member to the firearm; 
         [0010]    an adjustable member carried on the mounting member and adjustably movable upwardly and downwardly relative thereto; 
         [0011]    the sighting element being mounted on the adjustable member so that the upward and downward adjustment acts to change the height of the sighting element on the firearm so as to compensate for projectile drop over different distances; 
         [0012]    a manually rotatable wheel mounted on the mounting member for manual rotation by the user about an axis of the wheel; 
         [0013]    the wheel carrying a cam for rotation therewith having a generally spiral cam surface defining a spirally changing radius from the axis for engaging an abutment on the adjustable member and moving the adjustable member to a height determined by the radius at any selected position on the spiral cam surface; 
         [0014]    the wheel having a plurality of distance markings on a visible surface thereof angularly spaced around the axis for selection by the user of a required distance marking by rotating the wheel to a selected angular position determined by selection of the required distance marking; 
         [0015]    the spiral cam surface having a profile of radius changes calibrated such that the distance markings are each associated with a respective required height of the adjustable member. 
         [0016]    Preferably there is provided with the mounting member, sighting element and adjustable member a plurality of wheels each having a cam with a different profile of the cam surface where the cam spiral cam surface of each wheel has a profile of radius changes calibrated relative to a different shot load for the fire arm. 
         [0017]    Preferably the wheel is readily removable and replaceable for replacement with a second wheel having a cam with a different profile of the cam surface where the cam spiral cam surface of each wheel has a profile of radius changes calibrated relative to a different shot load. 
         [0018]    Preferably the wheel is readily removable and replaceable for replacement with a second wheel having a cam with a different profile of the cam surface where the cam spiral cam surface of each wheel has a profile of radius changes calibrated relative to a different fire arm. 
         [0019]    Preferably the wheel is attached to the mounting member by a single screw extending along the axis and defining a shaft for rotation of the wheel. 
         [0020]    Preferably the rear sighting element is mounted on the adjustable member for side to side movement for adjustment of the rear sighting element to compensate for windage. 
         [0021]    Preferably the rear sighting element is mounted on the adjustable member by an adjustment screw. 
         [0022]    Preferably the adjustable member is mounted on the mounting member by a pair of upstanding pins allowing sliding movement of the adjustable member on the mounting member. 
         [0023]    Preferably the pins carry springs for biasing the adjustable member onto the cam surface. 
         [0024]    Preferably the wheel is mounted between the pins below the adjustable member and the springs bias the adjustable member downwardly onto the cam surface. 
         [0025]    Preferably the wheel and the mounting member include cooperating elements for restraining the wheel in a plurality of angular positions corresponding to the distance markings on the wheel. 
         [0026]    Preferably the cooperating elements comprise series of recesses in one of the mounting member or the wheel and a spring biased ball for engaging into the recesses and carried on the other of the mounting member or the wheel. 
         [0027]    Preferably the mounting member comprises an upstanding block with a first upstanding side surface having the mounting elements for attachment of the mounting member to the firearm and a second parallel upstanding side surface carrying the wheel. 
         [0028]    According to a second aspect of the invention there is provided an adjustable rear iron sight for use with different firearms having different available shot loads comprising: 
         [0029]    a rear sighting element for mounting at a rear of the fire arm and defining a visible alignment portion for visual alignment by the user with a front sighting element; 
         [0030]    a mounting member having mounting elements for attachment of the mounting member to the firearm; 
         [0031]    an adjustable member carried on the mounting member and adjustably movable upwardly and downwardly relative thereto; 
         [0032]    the sighting element being mounted on the adjustable member so that the upward and downward adjustment acts to change the height of the sighting element on the firearm so as to compensate for projectile drop over different distances; 
         [0033]    and a plurality of manually rotatable wheels each arranged to be readily removably mounted on the mounting member; 
         [0034]    each wheel being arranged, when mounted, for manual rotation by the user about an axis of the wheel; 
         [0035]    each wheel carrying a cam for rotation therewith having a generally spiral cam surface defining a spirally changing radius from the axis for engaging an abutment on the adjustable member and moving the adjustable member to a height determined by the radius at any selected position on the spiral cam surface; 
         [0036]    each wheel having a plurality of distance markings on a visible surface thereof angularly spaced around the axis for selection by the user of a required distance marking by rotating the wheel to a selected angular position determined by selection of the required distance marking; 
         [0037]    each spiral cam surface having a profile of radius changes different from that of the other cam surfaces of the different wheels and calibrated such that the distance markings are each associated with a respective required height of the adjustable member relative to a different shot load for a selected fire arm. 
         [0038]    According to a third aspect of the invention there is provided an adjustable rear iron sight for a firearm comprising: 
         [0039]    a rear sighting element for mounting at a rear of the fire arm and defining a visible alignment portion for visual alignment by the user with a front sighting element; 
         [0040]    an upstanding mounting block with a first upstanding side surface having mounting elements for attachment of the upstanding mounting block to the firearm and a second parallel upstanding side surface; 
         [0041]    an adjustable member carried on a top of the upstanding mounting block and adjustably movable upwardly and downwardly relative thereto; 
         [0042]    the sighting element being mounted on the adjustable member so that the upward and downward adjustment acts to change the height of the sighting element on the firearm so as to compensate for projectile drop over different distances; 
         [0043]    a manually rotatable wheel mounted on the second side surface of the upstanding mounting block for manual rotation by the user about an axis of the wheel extending at right angles to the second side surface; 
         [0044]    the wheel carrying a cam for rotation therewith having a generally spiral cam surface defining a spirally changing radius from the axis for engaging an abutment on the adjustable member and moving the adjustable member to a height determined by the radius at any selected position on the spiral cam surface; 
         [0045]    the wheel having a plurality of distance markings on a visible surface thereof angularly spaced around the axis for selection by the user of a required distance marking by rotating the wheel to a selected angular position determined by selection of the required distance marking; 
         [0046]    the wheel and the mounting member include cooperating elements for restraining the wheel in a plurality of angular positions corresponding to the distance markings on the wheel; 
         [0047]    the spiral cam surface having a profile of radius changes calibrated such that the distance markings are each associated with a respective required height of the adjustable member. 
         [0048]    The invention also provides a method of adjusting the rear iron sight of a firearm as described above in which the wheel is selected from a plurality of wheels each having a cam with a different profile of the cam surface where the cam spiral cam surface of each wheel has a profile of radius changes calibrated relative to a different shot load for a selected fire arm. 
         [0049]    The adjustable rear sight described herein may have one or more of the following features: 
         [0050]    allowance to adjust windage and elevation for a zero range; 
         [0051]    projectile drop compensation to allow a “dead on” hold at any selected distance; 
         [0052]    projectile drop compensation interchangeable to allow using non-standardized loads; 
         [0053]    multi-position stops at useful distance intervals; 
         [0054]    positive stops to prevent accidental movement; 
         [0055]    easy to see markings indicating distance interval; 
         [0056]    quick adjustment without needing to use tools. 
         [0057]    To attain these features, the arrangement described hereinafter provides a sight mounting block which mounts the sight to said firearm, said sight mounting block containing mounting holes to allow attachment to said firearm, a threaded mounting hole to allow for attaching the projectile drop compensation mechanism, a spring and ball that apply force to maintain the position of the interchangeable multi-position cam and cavities being dimensioned to cooperate with the springs and modified shoulder bolts that control the vertical motion of the aperture mounting block; a projectile drop compensation mechanism which comprises a mounting shoulder screw and an interchangeable multi-position cam that raises the aperture mounting block via the vertical elevation screw, said cam profile to match the trajectory of the particular firearm and load; an aperture mounting block containing threaded holes for fastening the shoulder bolts that control its vertical motion, a vertical elevation screw, a horizontal windage screw, a threaded aperture block and an aperture. 
         [0058]    To provide allowance to adjust windage, a horizontal windage screw is contained in the aperture mounting block. Turning the screw clockwise causes the aperture block and aperture to move to the right as a result moving the point of impact to the right and turning the screw counter-clockwise causes the aperture block and aperture to move to the left as a result moving the point of impact to the left 
         [0059]    To provide allowance to adjust elevation for the zero range, a vertical elevation screw is contained in the aperture mounting block. The point of the vertical elevation screw rests on the profiled section of the interchangeable multi position cam. With the cam set to its lowest setting, adjusting elevation for the zero range can be performed. Turning the screw clockwise causes the aperture mounting block to raise (containing the aperture block and aperture) as a result moving the point of impact higher. Turning the screw counter-clockwise causes the aperture mounting block to lower (containing the aperture block and aperture) as a result moving the point of impact lower. 
         [0060]    Projectile drop compensation is achieved by adjusting the interchangeable multi position cam to the desired distance setting that is the closest match to the distance from the target. The profiled section adds the necessary increase in elevation to the zero range due to its direct contact with the point of the vertical elevation screw. The profile which has been machined into the cam has been determined using ballistic data calculated from customer supplied load information and the spacing between the front and rear sight. If the customer wishes, additional interchangeable multi position cams can be purchased and the customer only needs to install the correct cam to be able to aim “dead on” at any distance selected between the minimum and maximum distance settings. 
         [0061]    The front face of the interchangeable multi position cam displays distance settings in large easy to read numbers and lines. The distance intervals are close enough to allow the average point of impact to be will be within 1″ of the zero range at every setting. The circumference is knurled to provide ease of adjustment. Cam position is maintained by pressure of the spring loaded ball located in the sight mounting block engaging depressions in the rear surface of the cam. 
         [0062]    Quick adjustments to the desired distance setting are ensured by fact that the sight is always ready to be adjusted. The precision fit of the parts controlling the linear vertical movement prevent any looseness that require additional parts to control in some designs of the prior art. Adjustment to any setting is always less than 1 turn. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0063]    One embodiment of the invention will now be described in conjunction with the accompanying drawings in which: 
           [0064]      FIG. 1  is a rear elevational view of an apparatus according to the present invention shown mounted to the rear of a fire arm shown is shown schematically only in part cross-section. 
           [0065]      FIG. 2  is a side elevational view of the apparatus of  FIG. 1 . 
           [0066]      FIG. 3  is a top plan view of the apparatus of  FIG. 1 . 
           [0067]      FIG. 4  is a rear elevational view along the lines  4 - 4  of the wheel and cam of the apparatus of  FIG. 1 . 
           [0068]      FIG. 5  is a rear elevational view along the lines  4 - 4  of the wheel and cam of the apparatus of  FIG. 1 . 
           [0069]      FIG. 6  is an exploded rear view taken in the same direction as  FIG. 1  of the apparatus of  FIG. 1 . 
           [0070]      FIG. 7  is an exploded rear view taken in the same direction as  FIG. 2  of the apparatus of  FIG. 1 . 
       
    
    
       [0071]    In the drawings like characters of reference indicate corresponding parts in the different figures. 
       DETAILED DESCRIPTION 
       [0072]    An adjustable rear iron sight  10  is provided for a firearm  11  for cooperation with a fixed front sight (not shown) where the user aligns the front and rear sights to aim the fire arm in a required direction. 
         [0073]    The sight comprises a rear sighting element  12  which is shown in the form of an aperture  13  carried in a screw-in insert portion  14  for mounting in a housing  15 . This is mounted generally at a rear of the fire arm and defines a visible alignment portion defined by the aperture for visual alignment by the user with the front sighting element (not shown). Other types of sighting elements can be used which allow the user to locate the rear sight relative to the front sight as are well known in the industry. 
         [0074]    In general, the element  12  is carried on an a mounting member in the form of a mounting block  16  having mounting elements  17  for attachment of the mounting member  16  to the firearm  11 . An adjustable member  18  is carried on the mounting member  16  and is adjustably movable upwardly and downwardly relative thereto. 
         [0075]    The sighting element  12  is mounted on the adjustable member  18  so that the upward and downward adjustment of the adjustable member  18  acts to change the height of the sighting element  12  on the firearm  11  so as to compensate for projectile drop over different distances. 
         [0076]    A manually rotatable wheel  19  is mounted on the mounting member  16  for manual rotation by the user about an axis  20  of the wheel. The wheel  19  carries a snail cam  21  for rotation therewith having a generally spiral snail cam surface  22  defining a spirally changing radius from the axis  20  for engaging an abutment on the adjustable member  16  and moving the adjustable member  16  to a height determined by the radius at any selected position on the spiral cam surface  22 . 
         [0077]    The wheel  19  has a plurality of distance markings  19 A on an outer circular visible surface  19 B thereof angularly spaced around the axis  20  for selection by the user of a required distance marking by rotating the wheel to a selected angular position determined by selection of the required distance marking. The markings are shown as 100 to 200 yards but can vary depending on the parameters of the fire are concerned. 
         [0078]    The spiral cam surface has a profile of radius changes calibrated such that the distance markings  19 A are each associated with a respective required height of the adjustable member and therefore of the sight  12  carried by it. 
         [0079]    The wheel  19  is cylindrical with an outer circular surface carrying the markings. A peripheral surface  19 C is knurled for finger adjustment. The wheel is readily removable and replaceable for replacement with a second wheel  19 D ( FIG. 4 ) having a cam  20  with a different profile  22  of the cam surface where the cam spiral cam surface of that wheel has a profile of radius changes calibrated relative to a different fire arm and/or to a different shot load. 
         [0080]    The wheel  19  is attached to the mounting block  16  by a single screw  25  extending along the axis  20  and threaded into the block  16  at female thread  26 . The screw  25  defines a cylindrical surface forming a shaft  25 A for rotation of the wheel. The block  16  is mounted on the fire arm by pins  17 A passing through holes  17  forming the mounting elements. It will be appreciated that the block must be manufactured to accommodate the different mounting pin arrangements required for different fire arms. This mounts the block upstanding along the side of the fire arm with a side surface  16 A immediately adjacent the side of the fire arm and an opposed upstanding parallel surface  16 B adjacent the wheel  19 . 
         [0081]    The rear sighting element  12  is mounted on the adjustable member  18  for side to side movement for adjustment of the rear sighting element to compensate for windage. This is effected by providing a thread  12 B on the sight  12  to cooperate with a screw  12 A mounted across an outwardly projecting portion  18 A of the adjustable member  18 . The screw  12 A is operable by a head not shown for fine screw adjustment across the portion  18 A of the sight  12 . 
         [0082]    The adjustable member includes a main body portion  18 B mounted on top of the mounting block by a pair of upstanding pins  28  and  29  allowing vertical sliding movement of the adjustable member  18  along bores  31  and  32  in the mounting block  16  on the pins. The pins are attached by a threaded connection  33 A,  33 B at the upper end to the main portion  18 B of the adjustable member  18 . The pins  28 ,  29  carry springs  34 ,  35  for biasing the adjustable member onto the cam surface  22  of the cam  20 . The springs apply a downward force on shoulders  28 A and  29 A of the pins relative to shoulders  31 A and  32 A in the block  16 . Downward movement of the portion  18 B is limited by an adjustable screw stop  38  in a bore  39  which buts against the top surface of the block  16 . The pins  28  and  29  are held in place in the bores  31 ,  32  by end caps which close the bores and allow the pins to slide though while locating the pin against side to side movement. 
         [0083]    The wheel shaft  25 A is mounted between the pins  28 ,  29  below the adjustable member  18  and the springs bias the adjustable member downwardly onto the cam surface so that the cam surface when rotated lifts the adjustable member  18  off the stop  38 . 
         [0084]    The wheel and the mounting member include cooperating elements  40  for restraining the wheel in a plurality of angular positions corresponding to the distance markings on the wheel. The cooperating elements comprise a series of recesses  40 A in the surface  19 C of the wheel  19  and a ball  40 B biased by a spring  40 C for engaging into the recesses  40 A. The ball  40 B is held in place by a screw  40 D engaged into a bore  40 E in the block  16 . 
         [0085]    Thus the upstanding block  16  includes the first upstanding side surface  16 A having the mounting pins  17 A for attachment of the mounting member to the firearm and the second parallel upstanding side surface  16 B immediately adjacent and carrying the wheel  19 . 
         [0086]    Thus the apparatus includes the sight mounting block  16  which mounts the sight to said firearm  11 , said sight mounting block containing mounting holes  17  to allow attachment to said firearm. The spring and ball  40  apply force to maintain the position of the interchangeable multi-position cam  20  and cavities  40 A. The block  16  cooperates with the springs  34 ,  35  and modified shoulder bolts  28 ,  29  that control the vertical motion of the aperture mounting block  18 . The projectile drop compensation mechanism further comprises the mounting shoulder screw  38  and an interchangeable multi-position cam and wheel assembly  19  that raises the aperture mounting block  18  via the vertical elevation screw  38  against which it abuts. The cam profile is arranged to match the trajectory of the particular firearm and load. The aperture mounting block  18  contains threaded holes  39  for fastening the shoulder bolts  28 ,  29  that control its vertical motion. The sight finally includes the horizontal windage screw  12 A, the threaded aperture block  12  and the aperture  13 . 
         [0087]    To provide allowance to adjust windage, the horizontal windage screw is contained in the aperture mounting block  18 . Turning the screw clockwise causes the aperture block and aperture to move to the right as a result moving the point of impact to the right and turning the screw counter-clockwise causes the aperture block and aperture to move to the left as a result moving the point of impact to the left 
         [0088]    To provide allowance to adjust elevation for the zero range, the vertical elevation screw  38  is contained in the aperture mounting block  18 . The point of the vertical elevation screw  38  rests on the profiled section  22  of the interchangeable multi position cam  20 . With the cam  20  set to its lowest setting, adjusting elevation for the zero range can be performed. Turning the screw  38  clockwise causes the aperture mounting block  18  to raise (containing the aperture block and aperture) as a result moving the point of impact higher. Turning the screw counter-clockwise causes the aperture mounting block  18  to lower (containing the aperture block and aperture) as a result moving the point of impact lower. 
         [0089]    Projectile drop compensation is achieved by adjusting the interchangeable multi position cam  20  to the desired distance setting that is the closest match to the distance from the target. The profiled section  22  adds the necessary increase in elevation to the zero range due to its direct contact with the point of the vertical elevation screw  38 . The profile which has been machined into the cam  20  has been determined using ballistic data calculated from customer supplied load information and the spacing between the front and rear sight. If the customer wishes, additional interchangeable multi position cams can be purchased and the customer only needs to install the correct cam to be able to aim “dead on” at any distance selected between the minimum and maximum distance settings. 
         [0090]    The front face  19 B of the wheel  19  of the interchangeable multi position cam displays distance settings in large easy to read numbers and lines. The distance intervals are close enough to allow the average point of impact to be will be within 1″ of the zero range at every setting. The circumference is knurled at  19 C to provide ease of adjustment. Cam position is maintained by pressure of the spring  40 C against the loaded ball  40 B located in the sight mounting block engaging the depressions  40 A in the rear surface  19 C of the wheel  19  of the cam. 
         [0091]    Since various modifications can be made in my invention as herein above described, and many apparently widely different embodiments of same made within the spirit and scope of the claims without department from such spirit and scope, it is intended that all matter contained in the accompanying specification shall be interpreted as illustrative only and not in a limiting sense.