US20120055058A1

US20120055058A1 - Enhanced service life bolt

Info

Publication number: US20120055058A1
Application number: US13/226,572
Authority: US
Inventors: Richard Picard; David Findlay
Original assignee: Smith and Wesson Corp
Current assignee: Smith and Wesson Brands Inc
Priority date: 2010-09-08
Filing date: 2011-09-07
Publication date: 2012-03-08

Abstract

A firearm having a stock and barrel attached to a receiver. Located within the receiver is an enhanced service life bolt. The enhanced service life bolt has a plurality of lugs. At least one lug has a reduced height that is shorter than the height of the other lugs. The enhanced service life bolt defines an extractor slot and the at least one reduced height lug is located adjacent to the extractor slot. The at least one reduced height lug is approximately twenty percent (20%) shorter than the other lugs. The enhanced service life bolt is constructed from a maraging stainless steel, such as 158 Carpenter Stainless Steel.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No. 61/380,806, filed Sep. 8, 2010, entitled “ENHANCED SERVICE LIFE BOLT”, the aforementioned application being hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to firearms and, more particularly, to an improved bolt design for a firearm which enhances the service life of the bolt.

BACKGROUND OF THE INVENTION

Many service firearms, such as the M4/M16 family of rifles, as discussed by Duncan Long in The AR-15/M16 A Practical Guide, Paladin Press, 1985 incorporated in its entirety by reference, employ ammunition that generates high bullet energies and velocities. An example of such ammunition is the 5.56×45 mm NATO or “M855” cartridge. Such cartridges generate relatively high temperatures and pressures within the firearm during use. The M4/M16 family of rifles typically employs a gas-operated bolt assembly that includes a multi-lug bolt and a barrel extension with which the bolt locks and unlocks in firing each round of ammunition. The bolt assembly also includes an elongated firing pin, a spring-loaded ejector and a spring-loaded extractor configured to releasably engage a cartridge as it is placed in the firing chamber.
When each round of ammunition is fired, the interlocked bolt receives a force that is transmitted from the face of the bolt to its lugs which, in turn, transmit the force to the corresponding lugs of the barrel extension. In particular, during discharge of ammunition a bending moment is exerted upon the bolt lugs when the bolt lugs engage the lugs of the barrel extension.
One potential issue resulting from the combination of temperatures and pressures generated during firing is an increase in wear of the bolt, and particularly an increase in wear of the bolt lugs. As a result of this increase in wear comes the possibility of reduced bolt life. Known bolt designs for the M4/M16 family of rifles typically have a service life of around 6,000-8,000 rounds, after which time the bolt must be replaced.
Accordingly, it is desirable to increase the bolt life of such firearms as much as practicable. More specifically, it is desirable to increase the bolt life of a firearm to beyond 13,000 rounds.

SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of the present invention to provide a bolt for a firearm having an enhanced life.
It is another object of the present invention to provide a firearm having a stock, a receiver, a barrel, and a bolt having an enhanced life through the use of a stronger tensile strength material.
It is another object of the present invention to provide a bolt having an enhanced life through the use of a material that is heat treated for improved impact resistance.
It is yet another object of the present invention to provide a bolt having an enhanced life through the use of at least one low profile bolt lug located on both sides of the asymmetrical section of the bolt.
The present invention provides an enhanced life bolt for a firearm that includes the use of a maraging stainless steel, a heat treatment to provide maximum impact resistance and at least one low profile locking lug to reduce the bending moment of the lug most prone to wear to achieve a service life of the bolt in excess of that expected from known bolt designs.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood from reading the following description of non-limiting embodiments, with reference to the attached drawings, wherein below:

FIG. 1 is an exploded perspective view of a prior art bolt design.

FIG. 2 is a rear view of the prior art bolt design of FIG. 1 showing the lugs on the bolt head.

FIG. 3 is a detailed perspective view of the prior art bolt design of FIG. 1 showing the head thereof.

FIG. 4 is a rear view of an enhanced life bolt in accordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a prior art bolt design for the M4/M16 family of rifles is shown. The bolt 12 has a proximal end 14, a distal end 16 terminating in bolt face 18 surrounded by an integral bolt head 20 and an integral cylindrical portion 22 disposed between the proximal end 14 and the distal end 16 along a longitudinal axis or bolt centerline 24. The bolt 12 also has a longitudinal opening 26 in the integral cylindrical portion 22 to receive an extractor 28.
As shown in FIG. 2, the bolt head 20 has a plurality of bolt lugs 30 with walls 32 extending integrally and radially outward therefrom. This prior art bolt design employs seven (7) lugs 30 to lock the bolt with the barrel extension during the firing of each round of ammunition. Each locking lug 30 is symmetrical and is substantially the same in terms of dimensional specifications. In addition, as further shown in FIG. 2, each locking lug is spaced the same distance, and extends outward the same distance, from the bolt centerline 24. With the prior art bolt shown in FIG. 2, each of the lugs 30 has the same height, h1, or 0.1065″ for the current M4/M16 family. Known M4/M16 bolts are often manufactured using 158 Carpenter Stainless Steel.
As stated above, the forces and temperatures generated during the firing of ammunition increases wear of the bolt 12, and in particular the bolt lugs 30. The wear of the bolt 12 mandates replacement of known bolts at around 6,000-8,000 rounds. As shown in FIG. 3, wear is often most prominent around either of the locking lugs 30 straddling the extractor slot 26. These areas of wear are designated by arrow, W.
Turning now to FIG. 4, the enhanced life bolt 50 of the present invention is shown. The bolt has substantially the same configuration as the prior art bolt design described above and shown in FIGS. 1-3, with a notable exception being the configuration of the bolt head and locking lugs. The enhanced life bolt 50 of the present invention is also manufactured from a stronger tensile strength material than that used for known bolts for the M4/M16 family of rifles that is heat treated for improved impact resistance. Preferably, a maraging stainless steel, such as Carpenter 465 Stainless Steel is used, although other materials exhibiting strong tensile strength and improved impact resistance over 158 Carpenter Stainless Steel can be used.
The bolt 50 includes two locking lugs 52 straddling an extractor slot 54, which are reduced in height as compared to the other lugs 56. In the preferred embodiment, the full height lugs 56 have a height h1 while the two locking lugs straddling the extractor slot have a height h2 that is less than h1. As shown, h1 is about 0.1065″. Preferably, h2 is about 0.0850″, or 0.0215″ (approximately 20%) less than h1. Other height configurations and relationships are also possible provided that the two locking lugs 52 straddling the extractor slot 54 are reduced in height as compared to the other lugs 56. This reduction in height differs from prior art bolt 12, as shown in FIGS. 1-3. The prior art bolt 12 has seven (7) equally sized lugs and the presently disclosed bolt 50 has five (5) lugs 56, sized substantially equivalently to the lugs of the prior art bolt 12, and two (2) low-profile lugs 52. The inclusion of the two low-profile lugs 52 eliminates the high contact point without sacrificing strength, which has been validated through finite analysis and physical testing.
The approximate 20% reduction in height reduces the bending moment on these two low-profile lugs. This reduction plus the changes made in material properties increase the service life of the bolt from 6,000-8,000 rounds to in excess of 13,000 rounds. In addition, the locking area is reduced approximately 10% from the prior art design. The reduction is offset by the improved tensile strength of the material.
Although this invention has been shown and described with respect to the detailed embodiments thereof, it will be understood by those of skill in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed in the above detailed description, but that the invention will include all embodiments falling within the scope of this disclosure.

Claims

What is claimed is:

1. A firearm comprising:

a stock;

a receiver connected with the stock;

a barrel connected with the receiver; and

an enhanced service life bolt located within the receiver; the enhanced service life bolt having a plurality of lugs, at least one lug having a reduced height being less than a height of another of the lugs.

2. The firearm of claim 1, wherein the enhanced service life bolt defines an extractor slot, the at least one lug having a reduced height being located adjacent to the extractor slot.

3. The firearm of claim 1, wherein the at least one lug having a reduced height being approximately twenty percent (20%) shorter than the height of another of the lugs.

4. The firearm of claim 1, wherein the enhanced service life bolt being constructed from a maraging stainless steel.

5. The firearm of claim 4, wherein the maraging stainless steel being Carpenter 465 Stainless Steel.

6. The firearm of claim 4, wherein the maraging stainless steel being heat treated to improve impact resistance.

7. An enhanced service life bolt comprising:

a cylindrical portion; and

a plurality of lugs extending radially outward along a distal end of the cylindrical portion, at least one lug having a reduced height being less than a height of another of the lugs.

8. The enhanced service life bolt of claim 7, wherein the at least one lug having a reduced height being approximately twenty percent (20%) shorter than the height of another of the lugs.

9. The enhanced service life bolt of claim 7, wherein the enhanced service life bolt defines an extractor slot, the at least one lug having a reduced height being located adjacent to the extractor slot.

10. The enhanced service life bolt of claim 7, wherein the enhanced service life bolt being constructed from a maraging stainless steel.

11. The enhanced service life bolt of claim 10, wherein the maraging stainless steel being Carpenter 465 Stainless Steel.

12. The enhanced service life bolt of claim 10, wherein the maraging stainless steel being heat treated to improve impact resistance.

13. A bolt head for a enhanced service life bolt, the bolt head comprising a plurality of lugs extending radially outward about a bolt face, two of the plurality of lugs being reduced height lugs, the bolt head defining an extractor slot, the reduced height lugs being positioned adjacent to each side of the extractor slot.

14. The bolt head of claim 13, wherein the reduced height lugs having a reduced height being approximately twenty percent (20%) shorter than a height of the other lugs.

15. The bolt head of claim 13, wherein each of the reduced height lugs provide a reduced bending moment during firing of ammunition being less than the bending moment of the other lugs.

16. The bolt head of claim 13, wherein the bolt head being constructed from a maraging stainless steel.

17. The bolt head of claim 16, wherein the maraging stainless steel being Carpenter 465 Stainless Steel.

18. The bolt head of claim 16, wherein the maraging stainless steel being heat treated to improve impact resistance.