By Charles Brown
The problem of heat, friction, and the corrosive elements of primer and propellant combustion have ever bedeviled weapons designers. In machine guns, because of their high rate of fire, this problem is likely the most acute.
Machine gun barrels are a high usage part, for every complete .30 caliber Browning in the M1919A4 family, the prime contractors, Saginaw Steering Gear Division of General Motors, Buffalo Arms Corporation and Rock Island Arsenal produced 5 barrels. One barrel was for the weapon and the remaining four were spares. In addition to prime contractor barrel production, additional barrels were manufactured on spare parts production contracts. This would explain the plethora of USGI barrels; many dating from the early war years still in existence.
When machine guns first appeared they were, for the most part, water cooled and the science of metallurgy in them was not particularly well developed. Machine gun designers tended to use the same barrel materials as rifles with varying degrees of success. After combat lessons learned the hard way in WWI, the concept of air cooled weapons took on a greater importance because of their lighter weight and relative ease of portability. In order to increase combat reliability of air cooled ground machine guns weapons designers began to look at better materials. The term “better materials” covers a multitude of evils and material selection, especially for machine gun barrels that had to balance a host of requirements that included everything from cost of material to expected life to ease of manufacture.
When development of the M1919A4 got to the stage where the barrel drawing D35233 was produced, the Army had adopted a new method of identifying steel and other materials to be used in production. Basically, they started using standard civilian methods of description. However, the Army being the Army, also assigned them a strictly Army system of nomenclature.
During the intra-war period the Ordnance Department, through the Ordnance Committee, began to adopt U.S. Army Specifications that were identified by a numerical code. These specifications were intended to establish standards for each material and also provide guidance to civilian producers of materials and manufactured components. If they had learned anything, the Ordnance Department recognized after WWI that the use of civilian production facilities to produce war materials, and the Ordnance Department’s ability to administer these production facilities, would determine the “winner” in the next World War.
Barrels for the Model of 1917 and Model of 1919 Tank Machine Gun were fabricated from “Chrome Carbon Steel” which was a very loose description meaning next to nothing to a metallurgist because there is no description of the proportions of chromium, carbon or any other elements added to the alloy. The American Iron and Steel Institute and the Society of Automobile Engineers established standard specifications for steel products where steel alloys were identified by a code common to all manufacturers. In January, 1936 drawings for the new M1919A4 began to specify the barrel stock as W.D.4150 steel, an alloy containing chromium, molybdenum, carbon, sulfur, silicon and other elements in specific proportions. The use of this alloy required a rather elaborate heat treatment process to be performed before machining operations.
By February 1940, the Ordnance Department had decided to change the specified alloy to WD 4150 Modified U.S. Army Specification 57-107-25, which contained calcium and was quenched and hardened before it arrived in rod form at the barrel maker, eliminating the need for heat treatment at the fabricating facility. The addition of the calcium and quenching vastly improved the working properties, and improved tool life. Large batch production of this alloy improved uniformity and WD 4150 Modified remained the standard for all steel .30 Caliber ground type Browning barrels until the end of their service life.
During WWII, the U.S. did not follow the practice of some foreign weapons manufacturers, especially the Japanese, by chrome plating bores and/or chambers. Chrome plating improves wear and corrosion resistance, however, the plating is deposited on the base metal slightly altering dimensions. Post war the Ordnance department used chrome plating primarily to reclaim worn parts, such as M1 rifle operating rod pistons and M1919A4 trunnions to their original dimensions until the concept of chrome plating bores took hold in the early 1950s.
Ordnance addressed the problem of machine gun barrel wear by using an alloy called Stellite. The whole business of “Stellite” barrels is somewhat confusing as the entire barrel is not made of Stellite. These barrels are an assembly of mostly steel parts, and only one of the four parts, the “Liner, bore”, is Stellite. Stellite is the trademarked name of a non-ferrous, cobalt-chromium alloy often combined with various other materials to produce the desired properties. It was developed by Elwood Haynes in the early 1900s. The trademark name “Stellite” is the property of the Deloro Stellite Company.
One common pre-war use for Stellite was valves, valve guides and valve seats in internal combustion engines. Stellite alloys have high melting points and extremely high wear and corrosion resistance making them very useful for applications like a machine gun barrel. Because of Stellite’s wear resistance it is difficult to machine. Usually the part is cast to near finished dimension and ground to final specifications. Parts made from Stellite are expensive to produce, however, by using the Stellite parts in high temperature/wear areas in combination with other less expensive and more easily fabricated materials like steel, the useful life of the assembly can be extended several times over.
The bore area just ahead of the chamber of a machine gun barrel is most subject to repetitive intense heat and friction, and in addition, prior to about 1954 when the U.S. Army’s primer composition for U.S. Caliber .30 service ammunition finally changed over to a non-corrosive mixture, barrels were also subject to the corrosive effects of hydroscopic salts produced by primer ignition. Because of a high barrel replacement rate on aircraft .50 Caliber Brownings, Ordnance began to look around for some way to increase barrel life. After much experimentation the decision was made to “line” the area directly ahead of the chamber which suffered the most wear firing the very powerful .50 caliber Browning cartridge. Ordnance began experimenting with Stellite barrel components for the Cal. .50 BMG in 1942, however, progress on adapting Stellite for barrel use dragged on until 1944 when a workable process to produce a Stellite bore liner for the Cal. .50 BMG was developed. This liner increased useful service life three to four times over standard barrels.
The M1919A6 barrel was chosen for the Stellite treatment because it’s a lighter barrel. It weighed about 4.8 lbs versus the A4 barrel weight of 7.47 lbs., causing it to wear faster than the A4 due to its reduced mass and inferior heat dissipation ability. The decision to make Stellite barrels the preferred A6 type was not reached until July of 1945; this would preclude very many, if any, Stellite A6 barrels from service use during WWII. The original Stellite barrel for the M1919A6 is an assembly consisting of the liner (the Stellite bore insert) C7162479, retainer (the steel chamber insert) B7162480, the tube (the steel barrel itself) D7162478, and a pin which held the retainer in place, BFDX1.
The barrel was only available as an “assembly.” The individual parts making up the assembly were not. This early type barrel assembly did not have a chrome plated front barrel bearing and chrome plated bore ahead of the liner but the tube and retainer portion of the assembly continued to be fabricated from 4150 Modified steel alloy until June of 1950 when the steel for the tube and retainer changed to several options. The Stellite liners were manufactured in 5 different outside diameters and were installed in tubes by selective shrink fit and held in place by the retainer and pin. The retainer has 5/8 x 18 NF male threads at the forward end that is screwed into the tube against the Stellite bore liner and pinned in place. From notes on the various drawings it appears that the barrels were rifled and finish chambered after assembly.
Stellite barrels can be easily identified, other than looking at the part/drawing number imprinted on the barrel, by carefully examining the chamber end. The seam between the steel retainer and the barrel tube along with the dimple from the installation of the pin, which locks the retainer to the tube, is clearly visible.
Drawing D7162785, the original Stellite barrel for the M1919A4, did not appear until January 27, 1950. The A4 Stellite barrel used the same liner, retainer and pin as the A6 Stellite barrel. The only difference was the contour of the tube. This assembly was only available until January 1952 when all of the individual parts for the M1919A4 and A6 barrel assemblies were redrawn and renumbered. The only apparent reason for this is to put the drawings on to newly designed drafting media which placed the Ordnance Department letter sized drawing medium in agreement with civilian ANSI letter size drawings.
From January 1952 until June of 1953 the newly numbered A4 barrel assembly D7148399 and the A6 assembly D7148400 did not have the chrome bore and front barrel bearing surface. The chrome plating was added after June 1953. The first textual mention of a Stellite barrel assembly for the A4 that we could locate is in ORD 7 SNL A-6 dated October 1951. This lists the assembly drawing as D7162785. Changes No. 1 to this document dated February, 1952 still shows the D35233 (now called 6535233) standard all steel A4 barrel and the D54559 (now called 6554559) the standard all steel A6 barrel with a note that the standard barrels were to be issued until the supply was exhausted and only then would the Stellite types will be issued.
From the outset, barrels for the ground type .30 calibers were required to be imprinted with the piece mark/drawing number and the manufacturer’s identification along with the Ordnance Department “flaming bomb” and the “P” indicating that the barrel had been proofed with a high pressure test cartridge. Barrels produced from the D7148399 and D7148400 drawings were also marked with heat resistant paint in 1/2-inch high letters. After 1947 when the War Department morphed into the Department of Defense, the practice of using the flaming bomb passed into disuse. Some barrels also contain markings applied by the manufacturer for their internal use. The subject of parts marking could turn into a never ending serial like the ones the author remembers in movie theatres in the early 1950s.
Originally, barrels were preserved with Cosmoline, wrapped in kraft paper and either packed in cardboard tubes stapled shut or crated in units of 10. The Army spent much time and money developing methods to preserve and pack stock in a way that the end user would not have to spend half a day scrubbing grease or Cosmoline off parts. The SACO-LOWELL A6 barrel shown was originally packed in September of 1962 and when opened in 2009 it was in perfect condition thanks to VCI paper wrapping and a VCI bore wick. The author has observed Saco produced A6 Stellite barrels dated as late as 1967. With the M1919/M37 reaching obsolescence the practice of using Stellite in the fabrication of light machine gun barrels faded into obscurity.
This article first appeared in Small Arms Review SAW (April 2012) |
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