US2847788A - Automatic shotgun choke - Google Patents

Description

Aug. 19, 1958 I L. A. TWIGG AUTOMATIC SHOTGUN CHOKE 2 Sheets-Sheet 1 Filed on. a, 1955 LESTER A. TWIGG INVENTOR AGENT L. A. TWIGG 2 Sheets-Sheet 2 9 A H N o I- u INVENTOR LESTER A. TW/GG AGENT Aug. 19, 1958 AUTOMATIC SHOTGUN CHOKE Filed 001;. 5, 1955 R on mm mm R 9 mm v 6t tes atent 2,847,788 Patented Aug. 19, 1958 AUTOMATIC SHOTGUN CHOKE Lester A. Twigg, Bethesda, Md.

Substitute for abandoned application Serial No. 321,810, November 21, 1952. This application Gctober 3, 1955, Serial No. 538,205

Claims. (Cl. 42-79) The present invention relates to adjustable shotgun chokes. More particularly, it relates to a choke which is attachable to the muzzle of a cylinder bore gun, so that the effective bore diameter may be altered automatically by the passage of a shot load therethrough.

This application is substituted for application Serial Number 321,819, filed November 21, 1952, now abancloned.

A typical example of the application of semi-automatic chokes for shotguns is found in field bird shooting, and in shooting doubles at the clay pigeon trap. Usually the choke is set at cylinder (no choke) for the first shot and at full choke or choke for the second shot. As it is probable that the first bird or clay target would be near to the shooter at the moment of the first shot, an open shot pattern first would be most appropriate. The shot is then dispersed over a greater area, and thereby increases the probability of securing a hit. If, however, the shooter misses at close range, continued use of an open shot pattern would be undesirable. As will be understood, an individual shot does not possess the lethality at extended range which it possesses at close range. Therefore, a more concentrated shot pattern is required for certain results. In addition, at extended ranges, the shooter has more time to aim his'fire precisely, and therefore a broad pattern is not required to insure hits.

Prior adjustable chokes of the manual type are unsatisfactory for rapid fire shooting simply because little time is available to manipulate the choke. Prior chokes of the automatic type have not proved successful for the reason that they are unreliable in operation. Frequently, automatic choke devices have been discarded in favor of a double-barrelled shotgun having one barrel cylinder bored and the other barrel choke bored. Such a gun dependably affords the appropriate shot pattern for the usual situation in which a hunter may find himself. However, double-barrelled guns are considerably more expensive than a single barrel type, and do not possess the desirable feature of providing a wide variety of shot patterns.

Accordingly, it is an object of the present invention to provide the means for obtaining varied shot patterns with two successive loads in a single barrel gun.

Another object of the present invention is the provision of a shotgun choke variable from a first degree of choke to a fuller, or more constricted choke, by the passage of the first shot load therethrough.

Still another object or the present invention is to provide a two-shot shotgun choke which possesses two preset choke conditions and which is simply and quickly reset to the initial choke condition after the second shot is fired.

Gther objects and advantages will become evident as an understanding of the invention is gained through consideration of the following detailed descriptions and the accompanying drawings.

In the drawings:

Fig. 1 is a perspective view of the choke of the present invention.

Fig. 2 is a perspective view of the component parts of the invention.

Fig. 3 is an elevation view of the invention, and

Fig. 4 is an axial section taken along the line 4-4 of Fig. 3.

Referring now to the drawings, and particularly to Figs. 1 and 2 thereof, where the invention is seen assembled and broken down into its component parts.

In their order of assembly, the components of the automatic choke 10 of the present invention include, a choke tube 11 and a compression tube 12, into which the forward portion of choke tube 11 is slidingly inserted. The choke tube 11 and compression tube 12 are then inserted into an adjusting cylinder 13, which, as is more fully explained hereinafter, limits the sliding motion of the compression tube 12, after the first shot is fired. The choke tube 11, compression tube 12 and adjusting cylinder 13 are secured in operative relationship by an internally threaded retaining tube 14, the threads of which engage mating threads on both the choke tube 11 and adjusting cylinder 13. Finally, a grip ring 15 is secured to the forward end of compression tube 12, to aid manual adjustment of compression tube 12. The choke 10 is then in fully assembled relationship as it appears in Fig. 1.

As the invention will be better understood by comprehension of its mode of operation, the function of its elements will first be briefly considered before commencing their detailed description.

The choke tube 11 functions, as is conventional, in prior adjustable chokes, to diminish the bore of the gun to which the choke I0 is attached. Accordingly, the bore of the choke tube is variable from cylinder to full choke by compression of its forward expandable portion 16. The compression is accomplished by a forward sliding movement of the compression tube 12, which is internally tapered from front to rear. As full choke may not be desired, the adjusting cylinder 13,is adapted to arrest the forward sliding movement of the compression tube 12 in any position intermediate between cylinder bore and full choke.

In Figs. 3 and 4, the details of the invention may be seen. The rear internal diameter of choke tube 11 is chosen to provide a snug fit with the outside diameter of the barrel of the gun (not shown), to which the choke is to be attached by threads 21 or other suitable means. The muzzle of the gun abuts against shoulders 22 which are formed by reducing the bore of the choke tube 11 to the diameter corresponding to the bore of the gun.

The forward end portion of the choke tube 11 is provided with a plurality of axially extending slots 23, spaced about the circumference of the tube. The slots thereby provide a plurality of fingers 24, Which constitute the variable diameter portion of the choke tube 11. The material of which the tube 11 is constructed preferably possesses sufiicient resilience so that the fingers 24 may be compressed inwardly without acquiring a permanent inward set.

The exterior of the forward portion 16 of the choke tube 11 is finished with a front to rear inward taper. Similarly, tapered internal surfaces of the compression tube 12 are provided so that a compression of the fingers 16 will be provided upon the forward sliding movement of the compression tube 12. Thus, commencing at 25, the external diameter of choke tube 11 tapers to a minimum external diameter at 26. At 27, the external diameter is enlarged to provide Walls of adequate strength in the region of the gun muzzle and to provide a rear stop to arrest backward movement of'the compression tube 12.

The Compression tube 12 is internally bored to mate closely with the exterior of choke tube 11 and is pro- 'vided with an interior taper corresponding to the ex- 'terior taper of the choke tube 11. The internal diam- 'eter of of compression tube 12 is greatest at its forward end and tapers to a minimum approximately at 26. The exterior of compression tube 12 is finished as a smooth cylinder.

The compression tube 12 extends beyond the forward end of choke tube 11 and thereby provides, as is explained hereinafter, the forces for causing its forward sliding movement. A flange 28 is turned on the rear end of compression tube 12 for the purpose of engaging a shoulder 29 turned internally on adjusting cylinder 13, cylinder 13 being bored to slidingly receive tube 12. Holes 37 may be provided in the forward portion of compression tube 12 to increase shot load drag forces and to reduce muzzle blast.

As will now be understood, the degree of choke depends upon the distance which the compression tube is allowed to travel in the forward direction. Therefore, by arranging the adjusting cylinder 13 to permit a variation of the distance separating shoulders 27 and 29, any desired degree of choke from cylinder to full choke may be obtained.

The retaining cylinder 14 and adjusting cylinder 13 are threaded together by threads 30, so that the adjusting cylinder 13 may be retracted into retaining cylinder 14. A flange 31 is formed at the rear end of adjusting cylinder 14 so that cylinder 14 may be firmly secured to choke tube 11 with adequate clearance preserved to permit the retraction of cylinder 13 within cylinder 14. Cylinder 14 may be secured to choke tube 11 by threads 32, or, if desired, by a tight press fit, since tube 11 and cylinder 14 are not required to move relative to each other. Grip ring 15 is secured to the forward end of choke tube 12 by set screws 33.

Referring particularly to Fig. 3, the compression tube 12, and adjusting cylinder 13 are graduated to indicate the degree of choke for which the device is set. An index pointer 35, labelled for 1st shot and 2nd shot settings, indicates by alignment with one of the graduations 36 the precise degree of choke obtainable for the first and second shots.

The graduations conform to conventional definitions of the various degrees of choke. Cylinder, of course, indicates the open choke position in which the choke bore corresponds with the gun bore, assuming the gun to be cylinder bored. In the case of a 12 gauge gun, a cylinder bore gun has a diameter of approximately .729 inch, and therefore the bore of the choke corresponds to this dimension when adjusted to cylinder. Again, conventionally, the full choke diameter is defined as .689 inch for a 12 gauge gun. Therefore, the taper of the choke tube 11 and compression tube 12 must be such to reduce the bore of the choke by .040 inch when thecompression tube is in its extended position. In one 12 gauge embodiment of the invention, .75 inch has been found to be satisfactory for the length of the taper, the rate of taper therefore being .0266 inch inward per inch of axial length.

In use the device functions as follows:

Adjusting cylinder 13 is rotated until the graduation indicating the desired degree of choke is aligned with the 2nd shot position of index 35. Compression tube 12 is then adjusted by sliding the same axially until the graduation indicating the desired degree of choke is aligned with the 1st shot position of index 35. Any degree of choke may be selected for the second shot and any degree of choke intermediate between that selected for the second shot and cylinder may be selected for the first shot. The selections illustrated in Fig. 3 are choke for the first shot and choke for the second.

Upon firing the first shot, as the load passes beyond the forward end of choke tube 11, invariably several of the shot or pieces of wadding contact the forward wall of compression tube 12. Frictional drag forces are thus created which cause the compression tube to slide forward until flange 28 engages shoulder 29. This position provides the degree of choke preselected for the second shot. The choke is therefore automatically prepared for the second shot which may be fired immediately after the first shot. After firing the second shot, it is only necessary manually to retract compression tube 12 to the desired first shot choke condition. The cycle can then be repeated.

The features of the present invention which render its operation reliable, insure its long life, and simplify its construction include the elimination of spring loaded devices and devices operating by gas pressure. The operating forces of the present choke arise purely as a result of shot load drag. Furthermore, the force required for operating the choke is not large, since, by reason of the compression tubes extension beyond the end of the choke tube, compression of the choke tube is not required to be accomplished against the load pressure of the barrel. That is, with the load occupying the forward portion of the compression tube, the choke is effectively relieved of load pressure when the choke setting operation occurs. Gas pressure exists in the choke tube, however gas may leak through the slots 23 of the choke tube to equalize the pressure on both surfaces of the fingers 24. Thus only moderate drag force is required to move the compression tube forward to the second shot position.

Many modifications and variations are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. An automatic choke for firearms comprising, an expansible choke tube including a plurality of resilient fingers normally flexed outwardly to provide an open shot pattern, means for securing said choke tube to the muzzle of a gun, a second tube movably receiving said choke tube, said second tube projecting beyond the open end of said choke tube and being adapted for forward sliding motion relative to said choke tube, means on said second tube for flexing said fingers inwardly to provide a closed shot pattern upon movement of said second tube with respect to said choke tube, a third tube enclosing the rear portion of said second tube and including means for arresting forward movement of said second tube, and a fourth tube secured to said choke tube and adjustably receiving the rear portion of said third tube whereby the forward motion of said second tube may be arrested at intermediate choke stops.

2. A choke as claimed in claim 1 wherein said means for flexing said fingers inwardly comprises a tapered surface provided internally of said second tube,.said tapered internal surface bearing on the external surface of said choke tube.

3. A choke as claimed in claim 2 with additionally, means on said choke tube for indicating the longitudinal position of said second tube relative to said choke tube.

4-. A choke for firearms comprising, a first tube having a slotted forward end portion to provide a plurality of resilient fingers, said fingers normally being flexed outwardly to provide an easy shot pattern, means at the rear end portion of said first tube for securing said first tube to the muzzle of a firearm, a second tube slidingly enclosing said first tube and extending beyond the forward end thereof, said second tube including an outwardly directed shoulder at the rear thereof and having a tapered internal surface bearing on said slotted forward end portion of said first tube to flex said fingers inwardly upon sliding movement of said second tube with respect to said first tube, a third tube secured to said first tube so as to enclose the rear portion of said second tube and including an inwardly directed shoulder for engaging said shoulder on said second tube to limit the sliding movement of said second tube with respect to said first tube, and means on said first tube for indicating the longitudinal position of said second tube with respect to said first tube.

5. A choke for firearms comprising, a choke tube adapted to be secured to the muzzle of a firearm and having a slotted forward end portion for forming a plurality of resilient fingers normally flexed outwardly to provide an open shot pattern, said plurality of fingers each being provided with a tapered external surface, a compression tube slidingly enclosing said slotted forward portion of said choke tube and extending beyond the forward end thereof, said compression tube being provided with a tapered internal surface for hearing on said tapered external surfaces of said fingers to compress said fingers inwardly, a shoulder formed on said compression tube, an adjusting cylinder adjustably secured to said choke tube and receiving said choke tube and compression tube, a shoulder on said adjusting cylinder for engaging said shoulder on said compression tube, means including graduations along said compression tube for indicating in terms of degree of choke the longitudinal position of said compression tube with respect to said choke tube, and means including graduations along said adjusting tube for indicating in terms of degree of choke the longitudinal position of said adjusting tube with respect to said choke tube, whereby the drag forces created by the abrasion of shot against the forward Walls of said compression tube urge said compression tube forward and said shoulders into engagement thereby altering the bore of said choke tube in the amount indicated by said last a named means.

References Cited in the file of this patent UNITED STATES PATENTS

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