Gas cylinder attachment using a formed pin as orifice liner

Abstract

A spirally-wound, formed pin used as an orifice liner in a gas operated firearm. The spirally-wound, hollow, spring steel pin is useful in locating the gas cylinder on the barrel for the brazing operation and improves the location accuracy of the gas cylinder due to spring pin expansion. The spring pin tends to act as a protective liner to lessen the erosive effects of the explosive gases on the braze joint connecting the gas cylinder to the barrel.

Description

This invention relates to a gas operated firearm where high-pressure gas, produced by propellant combustion, is generally channeled from the bore of the gun barrel via a passage or orifice to an attached device, e.g. a gas cylinder, whereby the gas is allowed to impinge on areas of the firearm to provide various functions, e.g. force and motion to the firearm action, recoil attenuation, etc. More particularly, the invention relates to the use of a formed pin as an orifice liner to effect several important functions, which will be described later. Still more particularly, the invention relates to the use of a hollow, spring steel pin to locate the gas cylinder on the barrel for the brazing operation and which is spring-biased against the walls of the orifice in the gun barrel and the gas cylinder to improve the location accuracy of the gas cylinder due to spring pin expansion.

In many, if not most, of the currently produced gas operated sporting firearms the gas cylinders - of whatever type - are attached to the gun barrels with a braze joint using a silver "solder" as the brazing material. In this process, both parts are fluxed, held together with a silver "solder" preform sandwiched in between and heated to effect the braze joint. To prevent movement of the gas cylinder relative to the barrel, as the "solder" turns liquid, a locating pin is commonly used to align a hole in the barrel with a hole in the gas cylinder. Alignment of the gas cylinder rotationally and longitudinally relative to the barrel is achieved within the accuracy of the pin and hole tolerances while allowing the gas cylinder to move closer to the barrel, under a clamping force, as the "solder" preform melts.

Two problems may arise with this method of using a solid, cylindrical pin to locate the gas cylinder on the barrel during the brazing operation and drilling the gas orifice passages elsewhere in the interface braze joint. First, the accuracy of gas cylinder location is limited by the diametral fit between the locating pin and the blind holes in the gas cylinder and barrel. Second, the high velocity and pressure of the bore gas as it flows through the braze joint tends to erode the relatively soft braze material, creating an undercut ring area around the orifice hole. The presence of bore gas in this area, particularly if the braze joint is of poor quality, can cause a significant separative force between the gas cylinder and barrel possibly causing failure of the braze joint in tension. It should be noted that the joint strength can deteriorate rapidly, because not only does the eroded area create an increase in separative force, but it also decreases the tensile area remaining in the joint interface. Fortunately, shotgun bore pressures at the orifice hole are low, generally under 5,000 psi, with acceptable rates of braze erosion. Braze joint failures do occur, however.

In a currently produced semi-automatic rifle, the gas cylinder attachment is effected by utilizing a cylindrical pin to locate the gas cylinder on the barrel during the brazing operation and then axially drilling the gas orifice passage through the locating pin after brazing is complete. This method of using the locating pin body to shield the braze joint from the erosive effects of the gas is important in preventing braze joint failure when high orifice pressures of 50,000 psi - or greater - of present rifle cartridges is considered.

However, the latter method requires the post-braze drilling of the orifice hole and then externally sealing the orifice hole. This is accomplished in a manner described below.

It is an object of this invention to provide an econonical and easily positioned liner for a gas orifice hole in a firearm.

It is another object of this invention to provide a liner for a gas orifice hole in a firearm which tends to lessen the erosive effects of the explosive gases.

Still another object of the invention is to provide a liner for a gas orifice hole in a firearm which helps to accurately locate the gas cylinder on the gun barrel.

It is still another object of the present invention to provide an outwardly-biased formed pin to act as an orifice liner for a gas operated firearm.

Other objects will be obvious after reading the specification in which:

FIG. 1 is a sectional view of a prior art shotgun barrel having a gas cylinder brazed thereto.

FIG. 2 is a sectional view of a prior art firearm having a barrel with a gas cylinder attached thereto by a brazed joint which is partially eroded away.

FIG. 3 is a sectional view of a prior art firearm having a barrel and a gas cylinder attached and a gas cylinder locating pin acting as a gas orifice liner.

FIG. 4 is a sectional view of a firearm incorporating the present invention.

FIG. 5 is a sketch showing an exaggerated view of the spring pin locating the gas orifice where the barrel opening is larger than the gas cylinder opening.

FIG. 6 is a sketch showing an exaggerated view of the spring pin locating the gas orifice where the barrel opening is smaller than the gas cylinder opening.

FIG. 7 is a top view of a simple spring roll pin which is included in the present invention.

FIG. 8 is a top view of a spirally-wound spring pin which is the preferred form of the invention.

As mentioned above, the prior art is shown in FIGS. 1-3. FIG. 1 shows a currently-produced shotgun having a barrel 10 to which a gas cylinder 12 is attached by brazing 14. A locating pin 16 is used to align an opening 18 in the barrel with opening 20 in the gas cylinder. After the gas cylinder is assembled and brazed, a gas orifice 22 is drilled through the walls of the gun barrel and the gas assembly. As mentioned above, the rotational and longitudinal alignment depends on the accuracy of the pin 16 and tolerances of holes 18 and 20.

FIG. 2 shows a typical erosion of the braze joint interface of a modified gun barrel - gas cylinder attachment. Gun barrel 24 has a gas opening 26 which is in alignment with vertical gas opening 28 and longitudinal gas opening 30 of gas cylinder 32. The gas cylinder is attached by means of a brazed joint 34 which also has a gas opening 36 therein. It is noted that the gas orifice 38 of the firing system comprises the opening 26 in the gun barrel, opening 36 in the brazed joint, and vertical opening 28 of the gas cylinder.

In FIG. 2, the hatched portion 34a of the brazed joint is the original brazing and the unhatched portion 34b illustrates the portion of the brazed joint which has been eroded away.

FIG. 3 shows a currently-used method to alleviate the problem illustrated in FIG. 2. In this FIGURE, gun barrel 40 and gas cylinder 42 have step-drill holes 44 and 46 respectively. A solid, cylindrical pin 48 is inserted in the larger diameter portions of the step-drill holes to locate the gas cylinder 42 on the barrel 40 and then brazed in place. The gas orifice passage 50 is axially drilled through locating pin 48 after brazing is complete. It is noted that the braze at either end of the pin can and will be eroded in time but the area for the gas to act on is small, and limited to the end ring area of the pin. (See reference numeral 52 in FIG. 3.) Therefore, the finite maximum separative force can easily be estimated and allowed for in the design of the braze joint. This predictable design is obviously preferable to the unlined orifice hole where braze erosion and resultant loss in joint strength will proceed at an unknown rate.

However, this method (i.e. FIG. 3) requires the post-braze drilling of the orifice hole 50 which must then be externally sealed. This is accomplished by threading an outer length 50a of the hole, inserting a steel ball 54, holding the sealing ball in place with a hollow-hex head set screw 56, and staking the set screw to prevent loosening. As can be expected, the method of sealing the gas orifice opening is expensive.

The present invention is shown in FIGS. 4-8. FIG. 4 shows an exaggerated view of a gun barrel 58 - gas cylinder 60 assembly incorporating a spirally-wound spring locating pin 62. Spring pin 62 comprises a hollow spring steel pin and is used to locate the gas cylinder 60 on the barrel 58 for the brazing operation, acting between the larger diameter portion of the step-drill holes 64 and 66 in both the barrel and gas cylinder. Step-drill holes 64 and 66, when aligned, comprise the orifice hole 68. The joint is fluxed, assembled and preform-brazed in the normal manner. No additional machining or drilling of the orifice hole 68 or sealing the orifice hole with a separate ball and set screw is necessary or desirable. In addition to this economy, the tendency of a hollow spring pin to expand in diameter, until confined, means that the clearances that normally would exist between a solid pin and orifice holes are "absorbed" by this expansion in each hole, thus improving the location accuracy of the joint. See FIG. 4.

In summary, the use of a spring pin as the locating pin not only retains the advantages of the solid, drilledthrough pin in preventing braze interface erosion and joint failure and limiting erosion to the small and predictable ring area at pin end, but it also: (1) improves the location accuracy of the gas cylinder due to spring pin expansion, and (2) provides greater economy by eliminating post-braze drilling and the seal ball and set screw.

FIG. 5 shows an exaggerated, schematic view of a spring locating pin 62 used to align opening 70 of barrel 72 with opening 74 of gas cylinder 76 wherein the enlarged portion 70a of step-drill hole 70 of the barrel has a greater diameter than the enlarged portion 74a of step-drill hole 74 of the gas cylinder. When this happens, the spring pin 62 assumes the position shown in FIG. 5 and engages the gas cylinder at points A and the barrel at point B.

FIG. 6 shows an exaggerated, schematic view of a spring locating pin 62 used to align opening 78 of barrel 80 with opening 82 of gas cylinder 84 wherein the enlarged portion 78a of step-drill hole 78 of the barrel has a smaller diameter than the enlarged portion 82a of step-drill hole 82 of the gas cylinder. In this case, the spring pin 62 assumes the position shown in greatly exaggerated form in FIG. 6 and engages the barrel at point C and the gas cylinder at point D.

In either case, i.e. FIG. 5 or FIG. 6, the spring pin 62 is biased against the barrel and gas cylinder walls to accurately locate the openings and accurately position the gas cylinder on the barrel.

FIG. 7 shows a top view of a simple roll pin 62a which has been successfully used in attaching gas cylinders to model and test-bed rifles. However, flux does enter the orifice passage via the longitudinal slot 84 in the pin 62a and small quantities of gas acted on the braze interface via this slot.

A preferred, spirally-wound spring locating pin 62b is shown in FIG. 8. Because of the labyrinth form of the pin, the flux is prevented from entering the orifice passage and the explosive gases are prevented from contacting the braze point area on the sides of the elongated pin 62b.

Claims

What is claimed is:

1. A firearm having an elongated barrel through which a projectile means is propelled by explosive propellant gases, an orifice, in said barrel for bleeding off said explosive gases after the projectile means has passed the orifice, a gas cylinder positioned adjacent to said barrel and having an opening in substantial alignment with said barrel orifice, a hollow spring pin means positioned in and biased outwardly against the barrel orifice and the gas cylinder opening for accurately locating and aligning the orifice and opening for permitting the explosive gases to pass from the barrel through the pin means to the gas cylinder, and means securing said hollow spring pin means to said barrel and gas cylinder.

2. A firearm as recited in claim 1 wherein said hollow spring pin means comprises a cylindrical length of tubing having a slot running the length of said tubing and in the same direction as the axis of said tubing so that the slit tubing is free to move to a smaller diameter for insertion into said barrel orifice and said gas cylinder opening and then be spring-biased outwardly against the walls of the barrel orifice and the gas cylinder opening to align said orifice and opening and hold said slit tubing in place.

3. A firearm as recited in claim 1 wherein said hollow spring pin means comprises an elongated pin having a labyrinth form in which an inner free end is overlapped by an outer free end, thus permitting the pin to move inwardly to a smaller diameter and then be biased outwardly while defining an enclosed, gas-sealed passageway through which the explosive gases can pass from the barrel to the gas cylinder.

4. A firearm as recited in claim 3 in which said means securing said hollow spring pin means to said barrel and gas cylinder is a braze joint which is effected after the spring-biased pin is in position.

5. In a firearm wherein high-pressure gas produced by propellant combustion is channeled from the bore of a barrel via a passage to an attached gas cylinder device whereby the gas is allowed to impinge on areas to produce force and motion to the firearm action, the improvement comprising a hollow locating and aligning pin means positioned in said passage and secured to said barrel and to said gas cylinder device, said pin means comprising an elongated roll-type pin which is spring-biased against the walls of said passage, and means to rigidly secure said pin to said gun barrel and gas cylinder device whereupon the pin acts as a liner for the passage.

6. In a firearm as recited in claim 5 wherein said passage comprises step-drill holes in the bottom portion of the barrel and the top portion of the gas cylinder device so that when aligned, the step-drill holes will constitute a continuous passageway from the inside of the barrel to the inside of the gas cylinder device, said hollow pin means being positioned in and acting between the larger diameter portion of said step-drill holes in both the barrel and attached gas cylinder device and being spring-biased outwardly so as to accurately locate the step-drill holes and form the gas passageway.

7. In a firearm as recited in claim 6 wherein said means to rigidly secure said pin to said gun barrel and gas cylinder device comprises a braze joint which is formed after the pin means is inserted and is biased outwardly to align the step-drill holes.

8. In a firearm as recited in claim 5 wherein said pin means comprises a spirally-wound strip of flexible metal which has one free end thereof overlapping the other end to provide an enclosed inner opening which constitutes the passageway for the high-pressure gas, said spirally-wound metal strip pin being capable of being constricted to a smaller diameter and inserted into the passage between the barrel and gas cylinder device where upon being released the pin springs outwardly into engagement with the walls of the passage to act as a liner for the passage.

9. A liner for a high-pressure gas orifice connecting a barrel of a firearm and an attached gas cylinder comprising an elongated spring pin which is biased outwardly against the walls which define the orifice to accurately align and locate the orifice in the firearm with the orifice in the gas cylinder and to position the cylinder on the barrel.

10. A liner for a high-pressure gas orifice as recited in claim 9 wherein said spring pin comprises a spirally-wound pin having an outer portion overlapping an inner portion so as to eliminate any gap through which said high-pressure gas might leak.