US2387788A - Trigger - Google Patents

Description

C. 30, 1945. R, wlLEs 2,387,788

TRIGGER Filed July 9, 1943 Paiented Oct. 30, 1945 TRIGGER Application July 9, 1943, Serial N0. 493,959

13 Claims.

This invention is a trigger and is described herein and illustrated in the accompanying drawing, in which:

Figure 1 is a longitudinal section` (partly in elevation) of a rifle action including the trigger; Figure 2 is a graph showing the characteristics of the type of spring used., and for contrast those of an orthodox spring; Figure 3 is a graph illustrating the characteristic of the. trigger in different applications; and Figures 4-'7 are diagrammatic representations of the triggers graphed in Figure 3.

Good triggers may have a preliminary safety pull or slack as found in e. g. the U. S. Army rifle Model 1903 (Springfield), or this slack may be omitted as in most arms made for civilian use, e. g. the Winchester 52 target rifle. In either event, after the slack is taken up, if there isV slack, the trigger in the trigger pull proper should not move at all until thev required force is applied, and it should then move instantly and rapidly through the whole releasing movement (like breaking a small glass rod) and should be positively arrested or stopped as soon as possible to eliminate back-slap,

The major diiculty in trigger action is drag. In weapons of the highest grade with small tolerances, the overlap of the disengaging surfaces may be made so small, and the surfaces may be honed so smooth that drag is quite imperceptible. First class triggers are quite customary in the best arms. However, even the best arms often wear so that the nceessary trigger weight is lost or the surfaces wear rough so that the drag becomes objectionable. In cheaper arms a considerable overlap of the disengaging surfaces is required to meet necessary tolerances, and these surfaces are `often so rough initially, or wear so rough in use, that the pull is usually poor, Ay skilled marksman applies pressure to the trigger Very gradually,

so that when the trigger starts, he is exertingA no more pressure than isneeded, so that a rough spot in the surfaces is often quite enough to stop the disengaging movementI until more pressure is applied. Thus poor triggers move in a series the trigger occurs against a spring force less than that required to start its movement.

/sure buckle and curve as a plane at right angles,

corrugated disc springs, and many others.

Figure 2 is a graph showing force as ordinates andk displacement as abscissae. All the curves naturally start at the origin where force and displacement are zero. The line A by way of contrast shows the characteristics of a conventional spring, e. g. a helical spring, where lorce and displacement are lineally proportional.

The curve IB showsV the characteristics of the preferred type of spring. It rises from the origin like the curve of a conventional spring, but presently attens out, reaching a peak at b, descending with a negative slope to a minimum at b and then rising on a second positive slope. A study of this curve demonstrates that if the spring is displaced by a force such as that exerted by a screw, it will' move gradually through its whole course, the back pressure against the screw at each pointof displacement being represented by the ordinate at that point.

But if displacementl be effected by a followingup force like la weight, or like along helical spring where pressure is nearly as high at the end as at the beginning of the displacement, -or like the elastic muscles and tissues of the trigger linger wher-e pressure on the trigger is nearly as great at the end as at the start of its short movement, then when the spring is deflected just past the peak b of the curve, it will snap swiftly through the trough of the curve toa point b2 on the second position slope Where the force required to eect further deection again equals that exerted at the peak.

And during the entire snap movement the pressure required to keep the spring in'motion is well below that actually exerted on it at the peak, so that when used as a trigger spring, the excess force will sweep past anyv rough spots so that they will not be felt.

To get the best results, the spring should be so mounted that it is precompressed or predeflected to a point such as b3 below the peak on the negative slope. Then it cannot move at all until a force represented by the ordinate of that point is applied, and when such a force is applied by a follow-up elastic pressure, as by the finger, the entire movement is of the snap type.

The spring selected should have a steep enough negative slope that the spring force falls so fast that no rough spot on the engaging surfaces can raise the force to that required to start the movement. The length of the snap movement should be long enough to complete the disengagement before the force has risen very far on the. second positive slope of the curve. Furthermore, the spring mount should have a stop so that extra hard pressure on the trigger cannot break or strain the spring so as to modify the trigger pull.

Referring now to Figure 1, the spring (disc type) is shown applied to the wellknown Winchester 52 of the latest type. In this action II is the striker held in cocked position by the sear I2 pressed up by the sear spring I3 and held up by the engagement of the surface I4 on the trigger I5 with the surface I6 on the sear I2. On closing the bolt, the heavy spring I1 at the rear of the sear is compressed so that this spring forces the sear out of engagement with the striker when the movement of the trigger permits. The surfaces I4 and I6 on trigger and sear are the disengaging surfaces Whose relative movement controls the discharge of the piece. All the above parts and operations are well known.

The trigger spring is the disc I8 set in the cylindrical mount I9. Through the head of this mount extends ra anged button 2|, one end of which bears on a stud 22 on the trigger and the other end of' which bears on the spring I8. The opposite end of the mount I9 is closed by a threaded slightly dished'plug 23 which operates as a spring stop to prevent straining the spring, and to arrest the movementof the trigger when disengagement is completed. For purpose of clarity lthe curvatures of the precompressed spring and the plug are somewhat exaggerated in the drawing, permitting a trigger movement longer than required to disengage. In practice the spring throw is, as stated, so short as to arrest the Atrigger when disengaged. The plug is preferably perforated so that suction will not delay the return of the spring.

The spring is calibrated and adjusted as follows. Let us assume that, in view of the leverage, the spring should snap at 4 lbs. Springs are made to have a peak of the pressure deflection curves at say 4.8 lbs. Absolute uniformity will be difficult to attain, but variation will not be very important. The spring in its mount is located for adjustmentv with the button 2I up and a 4 lb. weight is applied to the button. This is not enough to deflect the spring past the peak of the curve. The plug 23 is then screwed in. This first presses the spring up until the flange on' the button contacts the head 20 of the mount, and then further defiects the spring (flattening it) until its force passes the peak and descends on the negative slope to a point where it snaps under'the 4 lb. weight. The spring is then adjusted exactly to the desired pressure.

In many types of locks the spring so mounted and adjusted can be fixed in any appropriate place to resist disengagement. But in the Winchester 52 lock, the sear acts also as the bolt stop and t release the bolt for cleaning must be ance Vto disengagement.

greatly depressed by an extra long powerful movement of the trigger. To permit this movement, the spring mount is slidably set in a cylinder 24 and pressed down by a heavy spring 25 against a threaded collar 26 by which the button 2| is adjusted to contact the stud 22 on the trigger.

yOn the application of the heavy pressure required to depress the sear for bolt removal, the spring mount moves up bodily against the spring 25 whose pressure is so high that, in firing, the trigger is effectively arrested when the spring strikes the dished face of the plug 23.

vConsideration will now be given to the characteristics of the lock to which the present spring may most advantageously be applied. For clarity reference is made to Figure 3 which illustrates the characteristics of several locks, and to Figures 4-7, which represent the trigger diagrammatically. In Figure 3, and in the diagrams, friction is ignored, and for clarity the trigger spring leverage is assumed to be 1:1 so that to get a 4 lb. trigger pull we use a 4 lb. resistance. These assumptions greatly aid clarity and simplicity of description.

First let us assume a lock, Figure 4, which inherently interposes a constant 2 lb. resistance to disengagement. This resistance may result either from the angle of the disengaging surfaces I4 and I6, particularly I6, or from the presence of a constant pressure trigger or sear spring resisting disengagement as in the case of the U. S. Army rie Model 1903 (Springfield) during the safety pull or taking up the slack, or it may be a result of both. It is represented in Figure 4 by the arrow marked 2 lbs. Y Y In Figure 3, the horizontal line D represents this constant force resisting disengagement. Now let us arbitrarily assume that the negative slope spring selected has its first maximum at 2.4 lbs.

and its minimum at 0.6 lb., i. e. the force at the minimum is 1A of that at the first maximum. Obviously the installation of such a spring predeiiected to 2 lbs. will give a trigger pull with the characteristics shown'by the curve D' which is simply the curve lof the spring added to the inherent 2- lb. constant resistance. The peak of the curve will be at 4.4 lbs., but, because of the predeflection, movement will start at 4 lbs., and the minimum pull will be 2.6 lbs. (2 lbs.i-0.6 lb.) The negative slope will be as shown.

Next yassume a lock with zero inherent resist- In the piece shown in Figure 1, this can be accomplished by grinding the disengaging surfaces, especially the surface I6 on the sear at the angle of repose for steel surfaces. Obviously, such a trigger will theoretically stay engaged'if no force is applied, but will move with a very light pressure. To get the desired 4 lbs. pull we may assume we use two disc springs, set together in parallel to give double force. This in some respects is a desirable way to get high spring pressures, because should one disc crack from fatigue, the lock will still operate, but with a lower trigger pull. ment is shown diagrammatically in Figure 5.

Under these conditions the Line D2 shows the inherent resistance of the trigger to disengagement (zero) andthe curve D3 shows the actual characteristics of the trigger pressure in its mount. The peak of the curve is4.8", and the minimum is 1.2 lbs. The double spring is predeiiected to start its snap movement at 4 lbs. on the negative slope-as before. This curve D3 has a steeper negative slope.

This arrangev l A. third condition, diagrammed in: Figure 6, is Where the disengaging surfaces, especiallyv that; on; the. sear, aref ground.` below the angle of repcseso that, in the absenceof. atrigger-or spring-,..sear spring or the like, the. trigger will automatically be forced out of engagement. The. Birmingham small arms Martini action is usually ground this Way, so that, if the triggerspring` breaks. andthe piece iscocked, While. manually holding the trigger forward; the striker orfiring pin will: fall as soon. as manuali pressure'v is.v` released; since the triggerv issubjected to a. con-fstant. negative, or disengagingi force: which is. overcome. only by the heavy trigger spring which normallyholds-f the.Y tip:- of the trigger under the shoulder on the tumbler. This'. disengaging-force may be represented diagrammatically bythe arrow'marke'd lbs-J in Figure. 6.

Let usi assume the negative or disengagingtorce. inherent in. the; trigger is; 2; lbs., as indi` cated bythe horizontal. line Dtrepresentinga. constant force o-f -2 lbs. Novvv to get a trigger. pull of; 4 lbs. We may take: three discs: piled to-` gether in parallel and the actual characteristics. of thetriggerwill be represented by-v the curve D5 Whose peak. is 5.-.2 lbs., predeflected. as before. to give a. starting pressure of; 4 lbs., and Whose minimum. is 0.2. lb. This curve not only has` avery steep. negative slopeadequate. to.v overcome;

the added. resistance of very rough spots in the:

drag,A but at. itsminimum.A isk actuallytending to.- movezby-itself. with no. nger. pressure at all. The

snap action is then very rapida In. thiscase thenegative force must bein part,I atleast, exerted through the. engaging surfaces. so that, on disengagement it. ceases toexist,A at. least tov su-.chan-.extent that the trigger will return. to normal position for re-cocking the piece.

While the preferred. spring has a. steep.` nega tive. slone. and. is.. predeiiected so. that its; move-- ment. starts on.. the negative. slope to.` the end that roughnesses even in the very start of. the drag arerendered. harmless. yet itl will be a-p.-v preciated that, during the rst positive slopeof. its. curve the spring actsr asan ordinary conven-A tional trigger spriIlg,.and;-isji1st.as goodin ever-'3rv respect.. most often develop toward. the end of the drag Where the engaging areas are reduced and the` higher unit pressures. tend to. produce. the greatest wear. Hence, trigger action superior tothe conventional action, but, inferior to. the. preferred action can be obtained by predeiiectingthefspring. to the peak of its curve or to a point. justv below the peak on the rst positive. slope. The trigger will'then act like a. conventionaltrigger during. the rst part of its .movement when roughnesses. in the drag are` less likely to occur., and will snap after the. short conventional movement So, as.- to.v overcome any rough spots toward the emi of. the. trigger movement. This is a less efficient. use than the preferred one wherein. trigger movement starts on the negative slope and through. its-Whole movement requires less force to move it than was required to start it.

Referring again to Figure 2', the curve. C shovvs the characteristics of another spring which. may, beused; Like the other curves, this startsY at the origin, rises at rst like the curve of the conventionalspring A, iiattens oii to a maximum c, falls to a minimum c., and again rises on a second positive slope. But this curve crosses the line of Zero force at c2 and rises to intersect it again at c3. A spring of this type snaps as before when deflected by a following-up force but,

Eurthermoraroughnesses.- in the dragsince. its forca falls belcwzero; it notreturxr..

tornormal on; the release or pressureabntinstead stopsfatthe pointicand; wilIjon-ly retnrmif forced baclr It' a.v reverse.- following-ups torce. iss' applied) to.- drive the springback. from. the: point c3 tofV Evidenth it. is theoretical-lypossible;v to use; a.

spring with: the; characteristics.- of; curve-f let it snap below.l zero,l andv return.- it by; sername;- chanical action. This would probably-- be too complex for practical use..

Fur-ther;` it: is'v known (see Spencer Patent; No.v

1,972,172)l that a spring with the characteristics of. curveB- (fEigu-re 2). is in4 realli-.y-v the. same; in: essence as one represented bycurve. plus;A ai

biaswhich keeps the curve.- at. all times above-zero This bias: isfy most conveniently.imparted` force.. asa set of the metal in manufacture; butit--mayf also, as shown; in. said Spencer-patenubeimpartei byA arseparateconventional spring. Hence, a com.-

posite spring may be the operative--equivalntzof' a` spring represented by cur-Ve B; although. less desirable from. a. manufacnniring=` standpoint..

Itv is.` alsoshown in said'y Spencer patent.r thati a..

reverse snap action occurs, when. a snapaction spring returns to position under the infiuencev. o1".y

at this point being 4 lbs.. 'Als the@ triggerr starts-1 against thev conventional spring, thesnap of the dischelps it along.- with ai constantly risingforce; the resultant of. the; composite atall-points being:

the force of the conventional; spring-.less that1of" thez disc. This-v curve.v is.r not graphed; but iti mayv coincide. closely withthe negative slope partof" curve.y 13;.

The springA is-Y hereinv illustratedas. of the disc type, because these are-easily available. and? their operation iswell known. In therile selectedto illustra the invention there is. ample spa-ce. forthe. installation. of this.- spring..

Howevery in many actions, the lateral.- thiol?- ness of the. Weapon may-'maker it. desirable. fm:

the purpose. of. reducing lateral dimension; .to use a spring of similar characteristics butrnarrower.. A. spring, for example., of the conned; arch@` type suggests` itself` as rea-@lilyy adaptable. tol narrowspa-ces,

The foregoing. detailed.. description. has. been given or-clearnessao understanding onlie.A and no vnnecessarv limitations should be; understood.

therefrom for. some modicationsv will. bes obvious-1 to. those. skilled. inthe art.

I claim:

1. In small arms, a spring impelled ring member which on movement from cocked position causes the discharge of the arm, a nger-controlled member, means operatively connecting the finger-controlled member with the ring member, said means including two surfaces adapted tol be disengaged, the first Aof which is moved by the finger-controlled member to release the second, and spring means resisting the disengaging movement, said spring means being of the type whose force deflection curve has a portion with a negative slope and being arranged to resist disengagement with a force which decreases during the disengaging movement.

2.. A'device according to claim 1 in which the spring means at the start of the disengaging movement exerts at least sufficient force t supply the necessary trigger pull weight.

3. A device according to claim 1 in which the surfaces are so related that except for the spring means, they will disengage and in which the spring means exerts the force required to prevent disengagement and to give in addition the necessary trigger pull weight.

4. In small arms, a spring impelled firing member which Yon movement from cocked position causes the dischargeV of the arm, a finger-'controlled member, means operatively connecting the finger-controlled member with the firing member, said means including two surfaces adapted to be disengaged, the first of which is moved by the finger-controlled member to release the second, and spring means resisting the disengaging movement, said spring means being of the type whose force deiiection curve has a portion with a negative slope and being arranged to resist disengagement With'a force which decreases from the start of the'disengaging movement and which throughout disengagement is less than at the start of disengagement.

5. A device according to claim 4 in which the spring means at the start of the disengaging movement exerts at least suiiicient force to'supply the necessary trigger pull Weight.

6. A device according to claim 4 in which the surfaces are so related that except for the spring means they will disengage and in which the spring means exerts rthe force required to prevent disengagement and to give'in addition the necessary triggerv pull weight.

7. In small arms,a spring impelled ring member which l'on movement from cocked position causes the discharge of the arm, a finger-controlled member, means operatively connecting the finger-controlled memberV with the ring member, said means including two surfaces adapted to be disengaged, the rst of which is moved by the finger-controlled member to release the second, and spring means resisting the disspring'means yat the start of the disengaging movement exerts-at least sufficient force to supply the necessary trigger` pull weight.

9. A device according to claim '7 ,in which the surfaces are so related that except for the spring means, they will disengage and inY which the spring means exerts the force required to prevent moved vby the nger-controlled member to release Y disengagement and to give in addition the necessary trigger pull weight.

10. In small arms, a spring impelled firing member which on movement from cocked posi- `tion causes the discharge of the arm, a fingercontrolled member, means operatively connecting the finger-controlled member with the ring member, said means including two surfaces adapted to be disengaged, the iirst of which is moved by the finger-controlled member to release the second, a spring of the type Whose force deiiection curve rises to a maximum and then descends with a negative slope, a mount for the spring, means in the mount to predeect the spring, and means operatively connecting the spring to the first surface to resist its disengaging movement.

11. In small arms, a spring impelled ring member which on movement from cocked position causes the discharge of the arm, axfmgercontrolled member, means operatively connecting the finger-controlled member with the iiring member, said means including two surfaces adapted to be disengaged, the first of which is moved by the nger-controlled member to release the second, a spring of the type whose force deflection curve rises to a maximum and then descends with a negative slope, a mount for the spring, means in the mount to predeflect the spring, means operatively connecting the spring to the` rst surface to resist its disengaging movement, and means in the mount to limit the deiiection of the spring.

12. In small arms, a spring impelled iiring member which on movement from cocked position causes the discharge of the arm, a ngercontrolled member, means operatively connecting the finger-controlled member with the ring member, said means including two surfaces adapted to be disengaged, the first of which is moved by the nger-controlled member to release the second, a spring of the type whose force deflection curve rises to a maximum and then descends with a negative slope, a mount for the spring, means in the mount to predeiiect the spring, means operatively connecting the spring to the rst surface to resist its disengaging movement, and means to adjust the position of the mount.

13. In small arms, a spring impelled ring member which on movement from cocked position causes the discharge of the arm, a fingercontrolled member, means operatively connecting the finger-controlled member with the iiring member, said means including two surfaces adapted to be disengaged, the first of which is the second, a spring of the type whose force delection curve rises to a maximum and then descends with a negative slope, a mount for the spring, said mount being movable, means in the mount to predellect the spring, means operatively connecting the spring to the first surface to resist its disengaging movement, and resilient means normally resisting bodily movement of the mount but providing for movement thereof under pressure markedly heavier than that exerted in disengagement.

. RUSSELL WILES.

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