Elric
Well-Known Member
Aperture Sight for the Cocking Piece By Val A. Fynn
American Rifleman, Volume 69, no 17 May 15, 1922, page 15-16
https://books.google.com/books?id=g...hDoAQglMAI#v=onepage&q=Aperture Sight&f=false
It is universally conceded that an aperture rear sight should be as near the eye as possible and that, in a bolt action rifle, the ideal location of such a sight is on the cocking piece. Unfortunately the cocking piece is movable when the arm is cocked and the position of any rear sight attached to it is therefore indefinite. Since with a 30" sight radius a displacement of the rear sight of 1/100th of an inch corresponds to a change of impact of 1.2 inches at 100 yards it is easily seen why such sights have not given general satisfaction. It does not appear that this defect can be eliminated by machining the bolt and receiver to closer limits. Substantially closer limits than now adopted in the best makes of bolt rifles are not practical for quantity production and even if they were all the play could not be taken out and the effect of wear at numerous points would still have to be contended with.
It has occurred to the writer that satisfactory results could be secured with an aperture sight on the cocking piece by providing means for positively locating said cocking piece, and therefore the rear sight, at the extreme end of its travel—when in the full cock position. The very fact that the play introduced by the unavoidable tooling tolerances allows the cocking piece to move practically in all directions makes it easy to positively locate it at any point of its travel without introducing undue friction or necessitating the use of appreciable effort. As soon as the trigger is pulled the cocking piece moves out of engagement with the locating means and completes its travel with no more interference than usual.
One way of carrying this idea into practice is shown in the accompanying sketch which diagrammatically represents part of the Springfield mechanism with the addition of one form of the means for positively locating the cocking piece. The aperture sight 9, a side view of which is shown, is dovetailed in the usual way into the head of the cocking piece 8, which is at full cock, and a steel skate 4 is rigidly attached to each side of the sight 9 in such manner as to retain constant space relation to said sight. A steel block 6, shown in longitudinal section, is firmly secured to the rearward projection of the receiver and to the stock as indicated by screws in the figure. This block is provided with two humps 5 adapted to cooperate with the skates 4 and separated by a groove which allows the withdrawal of the bolt and corresponds to a similar groove in the receiver. The cooperating surfaces on block and skates are preferably case hardened and highly polished, in this case they are supposed to be in one plane parallel to the axis of the bore. The edges of all four surfaces are rounded so as to facilitate engagement and minimize the risk of injury. The humps 5 are preferably so located that the last part of the action of cocking causes the skates to ride up on the humps without however forcing the cocking piece into a position outside the limits allowed by the available play. In this way it is possible to positively locate the cocking piece at the outer end of its travel without subjecting it to a severe strain and without introducing undue resistance against the forward movement of the cocking pin. The locating surfaces should be short in the direction of movement. Because of the sliding engagement the locating surfaces tend to keep automatically clean.
The arrangement of locating surfaces described in connection with the sketch will
prevent the cocking piece from rotating about its axis and will positively locate it in a vertical direction but may in some cases permit a transverse displacement when at full cock. To eliminate this last possibility it is only necessary to incline the locating surfaces on the humps 5 to wards each other and to shape the surfaces on the skates in a corresponding manner. Instead of a locating plane we will then have a V-shaped locating groove.
The block 6 can be attached to the tang only and this may be good enough although wood is not a reliable basis to fasten a locating surface to. The next best scheme is that shown in the sketch where the block is attached to the rearward projection of the receiver and to the tang. A better way is to braze the block to rearward projection but the best way of all would be to make the humps 5 integral with the receiver.
It may not be convenient to attach skates, or the like, to a sight as now sold nor may it be possible to provide the locating surfaces on some part of the sight mechanism. In such case it is quite simple to locate by means of flats cut on the knurled head of the cocking piece—independently of the sight mechanism—or on a collar secured to some part of the cocking piece, for instance to its waist just ahead of the knurled head. This is perhaps always the best arrangement since it does not interfere with the construction of the sight itself and also reduces the already small weight of the added parts. In this case a suitably shaped block is preferably brazed to the rearward projection of the receiver on each side of the groove accommodating the sear notch and an inclined locating surface tooled on each block.
Since the line of sight 3 is some distance from the axis 2 of the cocking piece, all displacements of the latter are magnified. It is best to keep the line of sight as close to the axis of the cocking piece as possible and the locating surfaces as far from that axis as may be.
Such a rear sight locating arrangement should be of particular value for the Mannlicher-Schoenauer.
American Rifleman, Volume 69, no 17 May 15, 1922, page 15-16
https://books.google.com/books?id=g...hDoAQglMAI#v=onepage&q=Aperture Sight&f=false
It is universally conceded that an aperture rear sight should be as near the eye as possible and that, in a bolt action rifle, the ideal location of such a sight is on the cocking piece. Unfortunately the cocking piece is movable when the arm is cocked and the position of any rear sight attached to it is therefore indefinite. Since with a 30" sight radius a displacement of the rear sight of 1/100th of an inch corresponds to a change of impact of 1.2 inches at 100 yards it is easily seen why such sights have not given general satisfaction. It does not appear that this defect can be eliminated by machining the bolt and receiver to closer limits. Substantially closer limits than now adopted in the best makes of bolt rifles are not practical for quantity production and even if they were all the play could not be taken out and the effect of wear at numerous points would still have to be contended with.
It has occurred to the writer that satisfactory results could be secured with an aperture sight on the cocking piece by providing means for positively locating said cocking piece, and therefore the rear sight, at the extreme end of its travel—when in the full cock position. The very fact that the play introduced by the unavoidable tooling tolerances allows the cocking piece to move practically in all directions makes it easy to positively locate it at any point of its travel without introducing undue friction or necessitating the use of appreciable effort. As soon as the trigger is pulled the cocking piece moves out of engagement with the locating means and completes its travel with no more interference than usual.
One way of carrying this idea into practice is shown in the accompanying sketch which diagrammatically represents part of the Springfield mechanism with the addition of one form of the means for positively locating the cocking piece. The aperture sight 9, a side view of which is shown, is dovetailed in the usual way into the head of the cocking piece 8, which is at full cock, and a steel skate 4 is rigidly attached to each side of the sight 9 in such manner as to retain constant space relation to said sight. A steel block 6, shown in longitudinal section, is firmly secured to the rearward projection of the receiver and to the stock as indicated by screws in the figure. This block is provided with two humps 5 adapted to cooperate with the skates 4 and separated by a groove which allows the withdrawal of the bolt and corresponds to a similar groove in the receiver. The cooperating surfaces on block and skates are preferably case hardened and highly polished, in this case they are supposed to be in one plane parallel to the axis of the bore. The edges of all four surfaces are rounded so as to facilitate engagement and minimize the risk of injury. The humps 5 are preferably so located that the last part of the action of cocking causes the skates to ride up on the humps without however forcing the cocking piece into a position outside the limits allowed by the available play. In this way it is possible to positively locate the cocking piece at the outer end of its travel without subjecting it to a severe strain and without introducing undue resistance against the forward movement of the cocking pin. The locating surfaces should be short in the direction of movement. Because of the sliding engagement the locating surfaces tend to keep automatically clean.
The arrangement of locating surfaces described in connection with the sketch will
prevent the cocking piece from rotating about its axis and will positively locate it in a vertical direction but may in some cases permit a transverse displacement when at full cock. To eliminate this last possibility it is only necessary to incline the locating surfaces on the humps 5 to wards each other and to shape the surfaces on the skates in a corresponding manner. Instead of a locating plane we will then have a V-shaped locating groove.
The block 6 can be attached to the tang only and this may be good enough although wood is not a reliable basis to fasten a locating surface to. The next best scheme is that shown in the sketch where the block is attached to the rearward projection of the receiver and to the tang. A better way is to braze the block to rearward projection but the best way of all would be to make the humps 5 integral with the receiver.
It may not be convenient to attach skates, or the like, to a sight as now sold nor may it be possible to provide the locating surfaces on some part of the sight mechanism. In such case it is quite simple to locate by means of flats cut on the knurled head of the cocking piece—independently of the sight mechanism—or on a collar secured to some part of the cocking piece, for instance to its waist just ahead of the knurled head. This is perhaps always the best arrangement since it does not interfere with the construction of the sight itself and also reduces the already small weight of the added parts. In this case a suitably shaped block is preferably brazed to the rearward projection of the receiver on each side of the groove accommodating the sear notch and an inclined locating surface tooled on each block.
Since the line of sight 3 is some distance from the axis 2 of the cocking piece, all displacements of the latter are magnified. It is best to keep the line of sight as close to the axis of the cocking piece as possible and the locating surfaces as far from that axis as may be.
Such a rear sight locating arrangement should be of particular value for the Mannlicher-Schoenauer.
