US20160010938A1

US20160010938A1 - Barrel extension

Info

Publication number: US20160010938A1
Application number: US14/794,790
Authority: US
Inventors: Zach Merkley; Chris Hunter; Dan Finlayson; Tim Larisch
Original assignee: Crosshill Technologies LLC
Current assignee: Crosshill Technologies LLC
Priority date: 2014-07-08
Filing date: 2015-07-08
Publication date: 2016-01-14

Abstract

A barrel extension used to attach a barrel to a rifle. The barrel extension includes a first end having a resistance fit surface with a cylindrical shape defining a diameter of an inner bore and an internal bolt locking lugs. A second end includes an extended section. An annular flange is disposed between the first and second ends. A threaded length extends a distance between the first and second ends and spans the annular flange to define a threaded connection length. The threaded connection length is about the same length as the diameter of the inner bore.

Description

BACKGROUND OF THE INVENTION

1. The Field of the Invention
The present invention relates to a device that connects the barrel of an AR-15 rifle, or other rifle to the upper receiver to improve accuracy.
1. The Relevant Technology
The present invention relates to firearms and specifically with a device that enables the removal of the barrel of a rifle. The barrel is replaced for various reasons. A longer barrel may be utilized to make far range shooting more accurate, while a shorter barrel is utilized for close range shooting, where quick maneuverability is required in close quarters and also to reduce the weight of the rifle. Another reason for this attachment method is to allow the replacement of the barrel with another type of barrel that offers various other desirable features such as barrel thickness. A further reason for replacement is created when the barrel rifling becomes worn due to usage of the gun, which causes reduction of accuracy. In this case, the barrel may be replaced with a duplicate barrel.
There have been various arrangements for securing the barrel of a firearm to the receiver or frame. One device as described in patent U.S. Pat. No. 8,479,429 B2 incorporates a spring-loaded quick coupling barrel retaining system. In this arrangement the firearm includes a receiver, a barrel nut, and barrel assembly rotatable mounted thereto. This arrangement includes locking lugs which rotatably engage and interlock with corresponding locking elements on the barrel nut splines. There is a spring member that self-tensions and tightens the lockup between the barrel assembly and barrel nut to provide the final fit.
While this spring locking device provides a relatively easy disconnect and reconnect, the inherent problem with this design is the continued tightness and structural stability that comes with of this type connection. Most operational conditions would not require the barrel to be quickly disconnected, especially if it meant sacrificing the structural soundness of the connection of the barrel to the receiver by not utilizing a threaded connection.
The other design that has been used in the past is one that is similar to the design described by U.S. Pat. No. 6,971,202. This arrangement utilizes a threaded nipple on the front of the receiver that receives a threaded cast aluminum or steel barrel nut having complementary mating internal threads. Except for the threading and sometimes castellated collar for gripping with a wrench, the barrel nut is a generally plain tubular structure and acts much as an ordinary nut. The breech end of the steel barrel has a short stub-like tubular extension that is equipped with an annular flange that is spaced inwards from the end of the extension. The barrel extension may be an integral part of the barrel or may be a separate tubular component that is threaded onto the breech end of the barrel. The barrel extension further contains internal bolt-locking lugs with angled feed ramps for loading cartridges into the chamber formed in the breech end of the barrel. The bolt-locking lugs in the barrel extension engage bolt lugs formed on the forward end of a rotatable and axially reciprocating steel bolt mounted in the receiver to provide a steel-to-steel lockup for withstanding the forces of combustion when the rifle is fired. The barrel is attached to the receiver by inserting the barrel extension through the threaded nipple into the receiver until the barrel extension flange is abutted against the receiver. The barrel nut is then slipped partially over the stub portion of the barrel and flange, and threaded onto the receiver nipple thereby trapping the barrel flange between an annular shoulder formed in the barrel nut and the receiver to secure the barrel.
In an alternative reverse arrangement of this type of barrel retaining system, the barrel nut may be externally threaded and the receiver contains a bore, having mating internal threads as shown in U.S. Patent Application Publication No. US2007/0033851. In either of the foregoing arrangements, the barrel is held to the receiver by trapping the barrel flange against the receiver with the barrel nut.
While the threaded design (the barrel extension and the barrel nut are both threaded) may take some additional time for disassembly and reassembly of the barrel extension, this design provides the most structurally sound design with these two threaded connections holding the barrel in place, as opposed to a spring loaded connection in the first example. In various cases, over time these connections are compromised to some extent. It is possible for the threads of the barrel extension to become severely stressed over time. On semi-automatic/automatic auto-loading rifles, like the military and law enforcement versions of the AR-15 and similar type carbines, these rifles experience extreme operating conditions of rapid-fire automatic weapons. This results in rapid wearing down of the rifling in the bore of the barrel, and excessive stresses on the barrel extension threads. The net result is that accuracy is compromised due to these conditions.
The prior art barrel Extension for the AR platform was designed around the concept of a light-weight barrel combat platform with “acceptable” accuracy standards. It was also designed to handle a rather small caliber cartridge as in the 5.56/.223 Remington. As the years have gone by, many improvements have been made to the AR platform to enhance performance, ergonomics, versatility and adaptability. The light- weight platform has been moved aside for a more reliable, accurate, and adaptable model concept. Additions of larger calibers in the similar basic platform, as well as longer and larger diameter/heavier weight barrels, have changed or exceeded the intent of the originally designed barrel extension. These changes in barrels are desired for their accuracy and performance enhancements, but they may fall short of their potential due to the weak link of being mated with a standard barrel extension that may not offer the support to these barrels. This invention of the barrel extension has updated this component and addressed the challenges these modern changes have posed to the AR platform.

BRIEF SUMMARY OF THE INVENTION

The improved barrel extension can be used with an AR-15 rifle, as well as other rifles, which meets the rigorous military specifications. This invention utilizes a threaded connection design for the AR-15 barrel extension with an internally threaded barrel nut holding the barrel in place. While this design may take some additional time for disassembly and reassembly of the barrel in comparison to the quick coupling barrel alternative design, it provides a more structurally sound design with threaded connections holding the barrel in place as opposed to a spring loaded connection provided with the quick coupling design. The barrel extension can provide the greater strength and rigidity needed in a modern high performing AR-15's and other rifles. This invention incorporates a barrel extension design that follows closely to typical mechanical engineering design requirements to provide adequate strength and resistance to deflection. It has been found that the main area of stress and deflection in the barrel extension is in the threads of the barrel extension where it screws into the breech end of the barrel of the rifle.
It is preferable that the threaded connection should be as strong, if not stronger, than the base material, in this case, the AR-15 barrel connection cylindrical section. In other words, the threads will not fail prior to the base material of the barrel extension.
The size of a threaded connection is first established by calculating the tensile load to be withstood by the threaded device and selecting a suitable size thread to withstand the tensile load with the appropriate factor of safety or preload. The AR-15 manufacturer should size the length of the threads to ensure that the threads will not be the weak link in the design. The diameter of the threads is not as much a variable as is the depth of the threads, since the diameter of the threads are somewhat fixed based on the size of the barrel and the caliber of the round being fired. Therefore, it is expedient that the manufacture determine the proper depth of threads to resist the stresses on the barrel extensions.
Accepted mechanical engineering and machining principles dictate that the maximum strength you can get from two objects threaded together is for the external threaded portion to enter into the internal threaded portion to a depth equal to the diameter of the external threaded portion.
It appears that one could theoretically increase the thread strength by increasing the length of engagement. However, the first thread will be taking the majority of the applied load. For carbon steel fasteners (including tapped holes) the length of engagement would be limited to approximately one nominal diameter (approximately 1½ times the diameter for aluminum). After that, there seems to not be an appreciable increase in strength. Once the applied load has exceeded the first thread's capacity, it can fail and subsequently cause the remaining threads to fail in succession.
Likewise, any thread length less than one diameter equivalent can provide a weaker connection where the threads can fail prior to the parent material; in this case, the cylinder of the barrel extension cylinder.
The prior art barrel extensions utilized a 13/16 inch diameter-16 UN thread, with an internal thread depth of about 0.620 inch. The major diameter or maximum diameter on a 13/16 inch-16 NC thread is about 0.920 inch. Utilizing the principal of maximum strength mentioned, the length of the thread should be at least about 0.920 inch. With the prior thread depth of about 0.620 inch, one can determine that the depth is short by about 0.1925 inch or a needed increase of 31% on the internally threaded barrel extension and its matching external threaded barrel to which it attaches.
This invention of the AR-15 barrel extension utilizes a design that meets the criteria of adequate thread depth to create the maximum holding capacity and can therefore minimize failure of the threads. This invention utilizes a 13/16 inch-16 UN thread with an internal thread depth of about 0.875 inch. Considering this new thread depth of about 0.875 of an inch and the major diameter of the 13/16 inch-16 UN threads still being about 0.920 inch on the externally threaded barrel we can determine that we are now about 0.0625 inch in excess of the required maximum strength depth with the AR-15 barrel extension. This therefore produces a stronger design, in excess of what is normally a required engineering practice, and in addition incorporating a safety factor of about 8%.
The barrel extension is responsible for holding and attaching the barrel to the upper receiver. The improvement to the barrel extension, when mated with any barrel or caliber, provides enhanced strength, chamber support and overall barrel support. It also can increases rigidity of the mated barrel and truer run-out in straightness tolerances.
In addition to the extra length of the thread depth on the mating parts of the barrel extension improvement and the upper receiver, the barrel extension improvement is now designed with a cylindrical extension of about 0.375 inch past the mating flange of the prior art extension. On the prior art design there was not an extension past the flange. With this additional extension past the barrel extension flange, there is a resulting moment carrying element to this barrel extension flange because the extra length of the barrel extension cylinder reduces the ability of the barrel to move or whip from side to side. This, therefore, can provide added side-to-side leverage and support, and help to control the harmonic whip of the barrel generated by the projectile traveling down the barrel. This can increase the accuracy by shortening the peaks and valleys in the tone generated by this projectile traveling down the barrel. This invention can also provide greater strength and rigidity to longer, heavier barrels in a greater variety of calibers. Many of the larger calibers introduced for the AR platform are much larger in diameter than the original 5.56/.223 Rem cartridge. These heavier longer barrels can weigh up to 3 times the originally intended barrel for use with the standard extensions. That means the chamber wall thickness is thinner and not as strong or stiff when reamed to these larger cartridge's dimensions. A cartridge chambered in one of the larger barrels may lack chamber stiffness and rigidity over the 5.56/.223 Rem chamber barrel. Due to these modifications to barrel, design creating generally longer barrels with greater weight due to diameter may not give maximum strength or potential that is intended.
Actual testing of this invention of the barrel extension has shown that by adding over-all length to the barrel extension and a longer threading surface can provide this enhanced performance required of the modified barrel designs.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present invention will now be discussed with reference to the appended drawings. It is appreciated that these drawings depict typical embodiments of the invention and are therefore not to be considered limiting of its scope.

FIG. 1 is a three dimensional enlarged image of the parts required to assemble the AR-15 carbine.

FIG. 2 is a three dimensional image of the AR-15 carbine showing how the barrel nut is being tightened with a barrel nut wrench completing the assembly of the barrel and the AR-15 barrel extension assembly to the AR-15 receiver.

FIG. 3 is a three dimensional image depicting the AR-15 assembly components with a comparison of the improved barrel extension and the prior art AR-15 barrel extension.

FIG. 4 a is a two dimensional drawing of the AR-15 rifle assembly cut-away showing the various components in an assembled position with the barrel extension installed. Adjacent to the cut-away drawing is an image of the barrel extension.

FIG. 4 b is a two dimensional drawing of the AR-15 rifle assembly cut-away showing the various components in an assembled position with the prior art AR-15 barrel extension installed. Adjacent to the cut-away drawing is an image of the prior art AR-15 barrel extension.

FIG. 5 a is a three dimensional front view of the prior art AR-15 barrel extension.

FIG. 5 b is a three dimensional front view of the barrel extension.

FIG. 6 a is a two dimensional cut-away view of an assembly of various AR-15 rifle components in a cut-away view with the barrel extension installed. Immediately below that drawing is a loading diagram showing how the loads would be distributed along the barrel assembly. The loading diagram depicts how the reactions to the barrel load are carried by the barrel extension.

FIG. 6 b is a two dimensional cut-away view of an assembly of various AR-15 rifle components with the prior art AR-15 barrel extension installed. Immediately below that drawing is a loading diagram showing how the loads would be distributed along the barrel assembly.

FIG. 7 a is a two dimensional front view of the barrel extension depicting the exterior of the device as well as the interior of the device shown in hidden lines. Detailed specifically is the sizing and placement of the threads with the major dimensions depicted so that it can allow the details of the design to be evaluated, such as the thread diameter and the thread depth.

FIG. 7 b is a two dimensional end view of the barrel extension depicting the orientation of the bolt locking lugs and sizing threads.

FIG. 8 a is a two dimensional front cut-away view of the barrel extension, which delineates the details of the threaded area in conjunction with the bolt locking lugs.

FIG. 8 b is a two dimensional end view of the barrel extension showing how the bolt locking lug orientation relates to the locating grooves.

DETAILED DESCRIPTION OF THE VARIOUS EMBODIMENTS

The AR-15 is a semi-automatic or automatic rifle that is used heavily in military and law enforcement applications. It has been modified over the years to provide improved features that allow higher caliber bullets, longer barrels for more accuracy, plus additional features added to the rifle that increase the loading applied to the AR-15 barrel extension—the device that ties the barrel into the receiver. The barrel extension includes the AR-15 rifle assembly, since it supports various barrels by being the link from the barrel to the upper receiver. The AR-15 barrel extension thereby solely supports and holds the barrels in position. In the past, while many changes were be made to the barrels and other components of this AR-15 rifle, there was little change to the mating/connecting device. As a consequence, there have been premature failures of the AR-15 barrel extension. This invention of the AR-15 barrel extension provides the needed modifications to match the changes that have evolved over time on the other rifle components. This design utilizes a new enhanced longer thread design that provides maximum strength for tensile loads on the threads and also provides increased ability for stabilization (resistance to bending or whip) of the barrel connection with this elongated AR-15 barrel extension design. Particular care is also taken in the heat treating and machining process to provide maximum life under maximum stressed conditions.
On semi-automatic/automatic auto-loading rifles, like the military and law enforcement versions of the AR-15 and similar type carbines, experience extreme operating conditions of rapid-fire weapons. This results in excessive stresses on the barrel extension threads and possibly excessive deflection in the barrel of the rifle. The net result is that the barrel extensions with the threaded design require replacement on occasion and accuracy is compromised due to these conditions.
Referring to FIG. 1, the three-dimensional image shows various components that make up the subassembly for the AR-15 carbine. The barrel extension 110 or other barrel extensions can provide the greater strength and rigidity needed in a modern high performing AR-15 and other rifles. The barrel extension 110 can be threaded onto the mating threads of the barrel 112 at the breech end of the barrel 113 to form the barrel assembly 115. Below the enlarged view is a small three-dimensional image of the barrel extension 110 in a stand-alone view to assist in visualizing the details of this part before being connected to the breech end of the barrel 113.
Subsequent to the barrel extension 110 being attached to the barrel 112, the barrel assembly 115 may then be inserted into the upper receiver 114. The insertion of the barrel assembly 115 into the threaded nipple 118 of the upper receiver 114 occurs when the barrel extension annular flange 116 is abutted against the threaded nipple 118. The barrel nut 120 is then slipped over the barrel assembly 115 and slid over the barrel extension annular flange 116. The barrel nut 120 is then threaded onto the threaded nipple 118 thereby trapping the barrel extension annular flange 116 between the shoulder of the barrel nut 120 and the shoulder in the threaded nipple 118. The barrel nut grip 124 is provided to allow the barrel nut to be tightened onto the threaded nipple.
FIG. 2 is a three dimensional illustration showing how the barrel nut 120 is tightened against the annular flange 116 to secure it to the upper receiver 114. A barrel nut wrench 122 is placed over the barrel nut 120 in a position where the internal gripping pattern (sometimes castellated collar) of the barrel nut wrench 122 can grip the matching external barrel nut grip 124 (this is sometimes a castellated collar). The barrel nut wrench 122 can then be utilized to tighten the barrel nut 120 onto the threaded nipple 118 while the AR-15 upper receiver 114 is held in place with a vice or other holding device.
Except for the barrel nut grip 124, the barrel nut 120 is configured as a generally plain tubular structure and acts much as an ordinary nut. The barrel nut 120 when fastened in the manner stated provides resistance against axial tensile stresses applied to the barrel assembly 115, and because the barrel extension annular flange 116 is captured between the barrel nut 120 and the treaded nipple 118 this joint also provides resistance to bending in the barrel assembly 115. In addition to the barrel extension annular flange 116 resisting the bending moment on the barrel assembly 115, the barrel extension 110 also provides resistance to the bending forces because it is fit snugly into the inner cylinder of the upper receiver 114.
It is therefore a requirement of the barrel extension 110 to take a similar axial or tensile load as the barrel nut 120 (which has larger threads) and in addition provide adequate strength to resist the bending loads in the barrel assembly 115. The barrel extension 110 therefore is responsible for providing resistance to the stresses that hold and attach the barrel to the upper receiver 114. The barrel extension 110 when mated with a barrel or caliber of rifle, gives you maximum strength and barrel or chamber support. This invention also increases rigidity of the mated barrel and truer run-out in straightness tolerances.
FIG. 3 is a three dimensional image of various components that make up a portion of the subassembly of the AR-15 carbine. This view depicts, as previously shown, the appropriate connection of the barrel extension 110 to the barrel 112 forming the barrel assembly 115. To facilitate alignment of the barrel assembly 115 with the upper receiver there is a set pin 121 provided in the barrel extension 110 which will be positioned within the threaded nipple 118 by means of a receiving slot 123. The set pin 121 is provided with a length such that when inserted into the threaded nipple 118, it may not project above the minimum diameter of the threads on the threaded nipple 118. Thusly, the barrel nut 120 may then be threaded over the threaded nipple 118 to complete the assembly.
In a detailed view, the components are shown in a side-by-side view to compare the existing AR-15 barrel extension 10 and the improved barrel extension 110. Both of these barrel extensions will work with the barrel as shown, but the improved extension has a much greater ability to resist the stresses inherent in rifle barrels.
FIG. 4 a is a two-dimensional cut-away view showing how the various components fit together and how they interact with one another. FIG. 4 a specifically shows the assembly utilizing the barrel extension 110. The threaded connection 128 extends past the barrel extension annular flange 116 to give a total thread length of dimension aim. The extended section 126 increases the threaded length 128 by a dimension e100 for threading into the breech end of the barrel 113. This extended section 126 provides additional shear stress capability in the threads, and it is also able to provide additional moment (side to side barrel deflection) carrying capability due to this extra cylindrical length e100. The improvement thusly enhances the strength of the assembly of the barrel receiver 110 to the barrel 112.
The barrel nut 120 encapsulates the old barrel extension annular flange 16 and ties the assembly together onto the threaded nipple 118 of the upper receiver 114. The barrel nut 120 holds the barrel assembly 115 axially to the upper receiver 114. The barrel nut 120 presses the barrel extension annular flange 116 into the upper receiver 114 threaded nipple 118 and due to the tight fit of the mating surface 127 of the barrel extension 110 against the inner cylinder 130. Because the barrel nut threads 132 are designed for shear loading and not a moment caused stress, and because the barrel nut threads 132 are larger in diameter than the diameter of the threaded connection 128 of the barrel extension 110, the barrel nut threads 132 are not required to be modified in length to meet the higher stress and moment criteria as is the case with the threaded connection 128 of the barrel extension 110. The barrel extension 110 is shown in FIG. 4 a with details of the interior of this device; specifically the internal threaded area.
FIG. 4 b is a two-dimensional drawing similar to FIG. 4 a. It depicts a barrel extension 10 and how it fits into a similar sub-assembly. The threaded connection 28 reduces the ability of the barrel assembly 15 to take axial and moment loading with this threaded connection 28. The barrel nut 20 is used for tightening the barrel extension annular flange 16 against the threaded nipple 18 attached to the upper receiver 14. The AR-15 barrel extension 10 is illustrated with the details of the interior of this device; specifically the threaded connection 28. The AR-15 barrel extension does not extend beyond the extension annular flange 16.
FIG. 5 a is a three-dimensional front view image showing details of the inside of the AR-15 barrel extension 10. One issue with this design is the depth of the threaded connection 28 and the fact that there is material to one side of the barrel extension annular flange 16.
FIG. 5 b is a three-dimension front view showing more detail of the inside of the barrel extension 110. It may be noted here that there is an extended section 126 including an amount of material added above the barrel extension annular flange 116. This additional material allows the depth providing a longer threaded connection 128, thereby adding strength to the barrel extension 110. The previous AR-15 barrel extension 10 has been used extensively for many years, but the improvement of the barrel extension 110 provides much greater allowances for resistance to stresses as typical for this device.
FIG. 6 a is a cut-away view of an assembly of various AR-15 rifle components with the barrel extension 110 installed. FIG. 6 b shows the old version of the AR-15 barrel extension 10. These two figures can be referred to jointly to compare the prior art (FIG. 6 b) with the improved barrel extension 110 (FIG. 6 a). The old AR-15 barrel extension 10 design can be compared against the improved barrel extension 110. The threaded connection provides a stronger connection than the old AR-15 barrel connection. The threads are less apt to fail in the improved barrel extension.
The size of a threaded connection is established by calculating the tensile load F10 to be withstood by the threaded device and selecting a suitable size thread to withstand the tensile load with the appropriate factor of safety or preload. The AR-15 manufacturer should size the length of the threads to ensure that the threads will not be the weak link in the design. The diameter of the threads d100 is not as much as a variable as is the depth of the threads a100 since the diameter of the threads d100 are somewhat fixed based on the size of the barrel and the caliber of the round being fired. Therefore, the depth of threads a100 may be sized to resist the stresses on the barrel extension 110. Accepted mechanical engineering and machining principles dictate that the maximum strength you can get from two objects threaded together is for the external threaded portion to enter into the internal threaded portion to a depth equal to the diameter of the external threaded portion.
The thread strength may be increased by increasing the length of thread engagement. However, the first thread will be taking the majority of the applied load. For carbon steel fasteners (including tapped holes) the length of engagement would be limited to approximately one nominal diameter (approximately 1½ times the diameter for aluminum). After that, there is no appreciable increase in strength. Once the applied load has exceeded the first thread's capacity, it will fail and subsequently cause the remaining threads to fail in succession. Likewise any thread length less than one diameter equivalent will provide a weaker connection where the threads will fail prior to the parent material; in this case the cylinder of the AR-15 barrel extension cylinder.
The existing AR-15 barrel extensions 10 typically use a 13/16 inch diameter-16 UN thread d10, with an internal thread depth of 0.620 inch a10. The major diameter or maximum diameter on a 13/16 inch-16 NC thread is 0.920 inch (d10). Utilizing the principal of maximum strength mentioned, the length of the thread a10 should be at least 0.920 inch deep. With the prior art thread depth d10 of 0.620 inch one can determine that the depth is short by 0.30 inch
The improvement ratio may be calculated as follows:
$Thread length Ratio = [\frac{a_{100}}{a_{10}}] = Thread tensile load carrying capacity factor$ $Thread length Ratio = [\frac{0.920}{0.620}] = 1.48 additional capacity ratio$
The lesser value of the diameter of the threads (0.920″) for the effective thread length versus the actual thread depth a110 of (0.875″) since there is no significant reduction in the stress due to tension after the thread depth a110 exceeds the diameter of the threads d110.
In addition to the extra length of the thread depth on the mating parts of the barrel extension 110 and the breech end of the barrel 113, the barrel extension 110 is now designed with a cylindrical extension 126 of 0.375 inch e100 past the barrel extension annular flange 116, toward the barrel 112. The prior art AR-15 barrel extension 10 had no extension past the barrel extension annular flange 16 (FIG. 6 b). With this additional extension past the barrel extension flange 116 there is created a significant increase in the resulting moment carrying element to the barrel extension 110. This is a result of the extra length of the barrel extension 110 decreasing the ability of the barrel 112 to move or whip from side to side.
The purpose of FIGS. 6 a and 6 b is to demonstrate the additional moment carrying capability provided with the threaded connection 128 of the barrel extension 110. Below is the formula for the maximum moment applied at the inner end of the barrel extension 110 at the threaded connection 128 as compared to the prior art AR-15 barrel extension 10 with and the threaded connection 28.
$M_{Max} = Maximum Moment$ $\begin{matrix} M_{Max} \end{matrix}$ $\begin{matrix} _{100} = \frac{w_{100} L_{100}^{2}}{2} & \begin{matrix} Maximum moment with the AR - 15 barrel \\ extension 110 (FIG . 6 a) \end{matrix} \\ M_{Max_{10}} = \frac{w_{1} L_{1}^{2}}{2} & \begin{matrix} Maximum moment with the prior art AR - 15 \\ barrel extension 10 (FIG . 6 b) \end{matrix} \end{matrix}$
By combining these two formulas we can calculate a ratio which will allow us to determine the effectiveness of this invention of the barrel extension 110 to reduce stress due to the bending moment in the prior art AR-15 barrel extension 10 due to the additional thread length on the threaded connection 128. First we calculate the maximum moment ratio:
$Maximum Moment Ratio = \frac{w_{100} L_{100}^{2}}{w_{1} L_{1}^{2}}$
As may be seen, the maximum moment (M_max) is proportional to the square of the length of the barrel L100 and proportional to the weight per inch of the barrel W100. If we assume, for example, that the weight barrel W10 has increased by 25% from the prior art barrel 12 design and the length of the barrel 12 has also increased by 25% then we can produce the following ratio.
$Maximum Moment Ratio = {[1.25] [1.25]}^{2} = 1.95 Ratio$
These ratios are examples of what may have occurred over time with the modification of the barrels 12. There are many designs that are available for different operations. Barrels 12 have been lengthened to provide better accuracy. They have been thickened to reduce deflection or to take larger bullets. Added features have been added to the barrels, such as heat shields to protect the user from the heat of the barrel. These changes add length and or weight which increase the bending moment M _max 10 at the barrel extension thereby causing additional stresses, and perhaps premature failure.
We can therefore determine that by increasing the length of the barrel 12 by 25% and the weight of the barrel 12 by 25%, we have increased the resulting maximum moment by a ratio of 1.95. This increased moment M _max 10 will now have to be taken by the AR-15 barrel extension 10. In order to determine what effect the maximum moment has on the threaded connection 128, versus the threaded connection 28, we need to show how this maximum moment affects the reaction loads (R100 and R10) in those threaded connections (128 and 28). The maximum bending moment is resisted by these positive and negative reaction loads R100 and R10 as shown in FIGS. 6 a and 6 b. We can develop a ratio formula as follows:
$\begin{matrix} {Reactions}_{100} = R_{100} = R_{100} = \frac{M_{{Max}_{100}}}{a_{100} / 2} & \begin{matrix} This calculates the reaction \\ loads in figure 6 a \end{matrix} \\ {Reactions}_{10} = R_{10} = R_{10} = \frac{M_{{Max}_{10}}}{a_{10} / 2} & \begin{matrix} This calculates the reaction \\ loads in figure 6 b \end{matrix} \end{matrix}$
To calculate the ratio of the prior art AR-15 barrel extension 10 against the improved barrel extension 110, and assuming no difference in the maximum moment applied to each design we can determine what benefit we would achieve with the barrel extension 110. Calculating the ratio:
$Reactions Ratio = [\frac{a_{10}}{a_{100}}] (Assuming moments are equal)$
This allows us to estimate the improvement ratio between the two designs. The more shallow threads in the threaded connection 28 provide much less resistance to bending in those threads than the longer thread length in the threaded connection 128. By comparing the prior art AR-15 barrel extension 10 against the barrel extension 110 and plugging in the appropriate thread lengths we calculate the following ratio (note we are here using the actual thread length d100 of 0.875″ since we are looking at bending stress (due to M _max 100 and not tensile stress (due to F100):
$Reactions Ratio = F Ratio = [\frac{{0.620}^{″}}{{0.875}^{″}}] = 0.71 Ratio$
The threaded connection 28 on the prior art AR-15 barrel connection 10 has been used for various sizes and lengths of barrel 12. This invention with the elongated thread design 128, thus, provides added side to side leverage/support and helps to control the harmonic whip of the barrel generated by the projectile traveling down the barrel. This can increase the accuracy by shortening the peaks and valleys in the tone generated by this projectile traveling down the barrel 112. This improvement can also provide greater strength and rigidity to longer, heavier barrels in a greater variety of calibers. Many of the larger calibers introduced for the AR platform are much larger in diameter than the original 5.56/.223 Rem cartridge. These heavier longer barrels can weigh up to three times the originally intended barrel for use with the standard extensions instead of the assumed 25% increase, referenced above. That means the chamber wall thickness is thinner and not as strong or stiff when reamed to these larger cartridges dimensions. A cartridge chambered in the larger barrels lacks chamber stiffness and rigidity over the 5.56/.223 Rem chamber barrel. Due to these modifications to barrel design 12 creating generally longer barrels with greater weight, the prior art AR-15 barrel extension 10 has been shown to be deficient in providing adequate strength that is required for these new barrel 12 designs.
The barrel extension 110 holds and attaches the barrel 112 to the AR-15 upper receiver 114. The improved barrel extension 110, when mated with any barrel or caliber, gives you enhanced strength, chamber support and overall barrel support. It can also increase rigidity of the mated barrel and truer run-out in straightness tolerances. Actual testing of the improved barrel extension 110 has shown that by adding overall length to the barrel extension 110 and a longer threading surface 128 does in fact provide this enhanced performance of the modified barrel designs.
FIG. 7 a is a front view of the barrel extension 110 depicting the exterior of the device along with the interior of the device shown as hidden lines. This view depicts the extended section 126 that extends past the barrel extension annular flange 116 providing additional strength to barrel extension 110 on the end that attaches to the breech end of the barrel of the rifle. To allow ease of threading the barrel extension 110 into the mating threads of the barrel, there is an entrance relief 134 provided before the threaded connection 128. The threaded connection 128 is shown and the length of that thread is depicted by a100. The diameter of the threaded connection d100 is the dimension that is used to determine the length of the threads a100. To achieve the proper depth of threads (a100), the dimension is at least equivalent to about the diameter of the thread d100. Adjacent to the threaded connection 128 on the opposite end is a thread relief 135.
Once the barrel is fastened to the barrel extension 110, the exposed end of the barrel extension 110 then displays the bolt locking lugs 136 that have been machined into the inner cylinder of the barrel extension 110. These bolt-locking lugs in the barrel extension 110 engage bolt lugs formed on the forward end of a rotatable and axially reciprocating steel bolt mounted in the upper receiver to provide a steel-to-steel lockup for withstanding the forces of combustion when the rifle is fired. In addition to the bolt-locking lugs 136, there are two internal angled feed ramps 138 in this similar end of the barrel extension 110 for loading cartridges into the chamber. Pull through broaching can be used to create the broach pattern of the bolt-locking lugs 136, cutting one or multiple groves at a time.
A set pin 121 is externally mounted and disposed into a receiving hole that is used as a locating pin that will be pressed into a receiving slot in the upper receiver. The set pin 121 may also be used as a torque device that enables the barrel extension 110 to be tightened into the receiving threads in the breech end of the barrel with a special torque tool matching the outer diameter of the barrel extension 110 and fixedly placed over the set pin, which may be used as an anchor while rotating and tightening the barrel extension 110 into the breech end of the barrel.
Some items in the manufacture of the barrel extension 110 are the barrel extension annular flange 116 and the resistance fit surface 140. The barrel extension annular flange 116 is the portion of the device, in the final assembly, that is sandwiched against the mating parts and is able to transfer the operational stresses from the barrel extension 110 into an AR-15 upper receiver. The operational bending stresses can be transferred through the controlled machined surface of the resistance fit surface 140 formed by the outside diameter of the barrel extension 110. The resistance fit surface 140 can slide into the receiving end of the upper receiver, thereby transferring the induced stresses into the upper receiver. Due to the tightly controlled tolerances of the resistance fit surface 140, the barrel extension is able to transfer the bending stresses into the body of the upper receiver by means of this barrel extension annular flange 116 and the resistance fit surface 140. A clearance ring 142 is cut into the outside diameter to allow the machining to occur with great accuracy for the full length of the resistance fit surface and allow tool disengagement prior to machining the extension annular flange 116. A CNC machine may be used to manufacture the barrel extension, which can be made from cold rolled steel and heat treated.
FIG. 7 b is a top view of the barrel extension 110 depicting the exterior of the device as well as the interior of the device shown in hidden lines and specifically the orientation of the bolt locking lugs 136 and the two angled feed ramps 138. This view depicts the entrance to the threaded connection 128 of the barrel extension 110. The barrel extension annular flange 116 is also shown in this view.
FIG. 8 a is a cross-sectional, front view of the barrel extension 110 with the dimension locations depicted illustrating the details of the design, such as the diameter of the thread d100 and the threaded connection length a100. The extended thread length enhances the design of the barrel extension. FIG. 8 a also shows the dimensions in the design of this device to compared them with the prior art AR-15 barrel extension 10. The cut-away view also allows better visibility of the entrance relief 134, the thread relief 135 along with the angled feed ramps 138 and the bolt locking lugs 136.
FIG. 8 b is an end view of the barrel extension 110, similar to FIG. 7 b, depicting how the angled feed ramps 138 are machined with a tool being fed into the barrel extension 110 on an angle to facilitate the entrance of cartridges into the barrel chamber. FIG. 8 b also illustrates the orientation of the bolt locking lugs. The angled feed ramps 138 matching up to the mating features of the upper receiver that the AR-15 fits into after being assembled with the barrel into an assembly.
The barrel extension has many design improvements such as stress capabilities, additional thread length to give maximum tensile load capability, and enhanced capability for more heavily loaded AR-15 barrel assemblies that are now more typical for the latest military and police operations. The design is more resistant to bending at the barrel extension. The longer thread length in the barrel extension provides lower reaction loads at the connection which provide longer life. The design is adaptable to the newer longer and heavier barrels. And provides additional resistance to harmonic whip action during shooting thereby increasing accuracy.
The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in various respects as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. Changes which come within the meaning and range of equivalency of the claims are to be embraced within their scopes.

Claims

What is claimed is:

1. A barrel extension for attaching a barrel to a rifle, the barrel extension comprising:

a first end including a resistance fit surface having a cylindrical shape defining a diameter of an inner bore and having an internal bolt locking lugs;

a second end including an extended section; and

an annular flange disposed between the first and second ends, wherein a threaded connection length extends a distance between the first and second ends and spans the annular flange, the threaded connection length being cut into the inner bore, the threaded connection length having a length substantially equal to the diameter of the inner bore.

2. The barrel extension of claim 1, wherein the second end further includes an entrance relief on an outer end positioned before the threaded length.

3. The barrel extension of claim 1, wherein the resistance fit surface further includes a set pin externally mounted and disposed into a receiving hole.

4. The barrel extension of claim 3, wherein the set pin is positioned within a threaded nipple of a receiving hole.

5. The barrel extension of claim 1, wherein the extended section is configured to extend beyond a barrel nut when assembled.

6. The barrel extension of claim 1, wherein the extended section is configured to provide an extra cylindrical length of the barrel extension.

7. A barrel extension for attaching a barrel to a rifle, the barrel extension comprising:

an annular flange configured to abut to an upper receiver to attach the barrel to the rifle using a barrel nut;

a first end extending out from a first side of the annular flange, the first end including a resistance fit surface having a cylindrical shape defining a diameter of an inner bore and an internal bolt locking lugs; and

a second end extending out from a second side of the annular flange, the second end including an extended section,

wherein a threaded connection length extends a distance between the first and second ends and spans the annular flange, the threaded connection length being substantially equal to the diameter of the inner bore.

8. The barrel extension of claim 7, wherein the second end further includes an entrance relief positioned opposite the annular flange.

9. The barrel extension of claim 7, wherein the extended section is configured to extend out past the barrel nut when assembled.

10. The barrel extension of claim 7, wherein the extended section is configured to extend the threaded connection length across an extra cylindrical length.

11. The barrel extension of claim 7, wherein the annular flange extend above the first and second ends.

12. The barrel extension of claim 7, wherein the second end is shorter than the first end.

13. The barrel extension of claim 7, wherein the first end is defined with a first diameter and the second end is defined with a second diameter, the annular flange is defined with a flange diameter, the first and second diameters being configured to be less than the flange diameter.

14. The barrel extension of claim 13, wherein the first diameter is substantially equal to the second diameter.

15. A barrel extension for attaching a barrel to a rifle, the barrel extension comprising:

a first end including a resistance fit surface having a cylindrical shape and an internal bolt locking lugs;

a second end including an extended section having a cylindrical shape and an entrance relief;

an annular flange disposed between the first and second ends; and

an inner bore having a diameter and extending between the first and second ends and spanning the annular flange, the inner bore including threads that span a threaded connection length over a distance between the first and second ends, the threaded connection length being substantially equal to the diameter of the inner bore.

16. The barrel extension of claim 15, wherein the extended section is configured to provide an extra cylindrical length.

17. The barrel extension of claim 16, wherein the threads in the threaded connection length span substantially across the across the extra cylindrical length.

18. The barrel extension of claim 15, wherein the annular flange extend above an outer diameter of the first and second ends.