M14 Rifle History and Development By Lee Emerson Preface



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Receiver Heat Treatment

According to USGI M14 receiver (drawing number 7790189) blueprints, the treatment procedure is as follows:

1. Recommended Heat Treatment - Normalize before machining (oil quenching followed by tempering at not less than 450 degrees Fahrenheit may be used in lieu of air cooling). Carburize at 1550 to 1600 degrees Fahrenheit to specified case depth. Oil quench from 1550 to 1600 degrees Fahrenheit. Temper to hardness specified.

2. Mandatory Requirements:

a. Normalize before machining.

b. Carburize to case depth 0.012 " to 0.018 ".

c. Temper one hour minimum at 350 to 450 degrees Fahrenheit.

d. Core hardness 28 to 42 HRC. Surface hardness 68 to 71 HRD.

e. Microstructure of core shall not contain more than 10 % free ferrite after heat treatment.

f. The use of a straight cyanide bath or gas processes shall not be permitted.

3. Inspection after Heat Treatment - After heat treatment each receiver shall be free from cracks, seams and other injurious defects as determined by magnetic particle inspection using a standard five turn magnetizing coil with a current of 400 to 500 Amperes.

The USGI specification for M14 receiver surface hardness is 56 to 60 HRC (68 to 71 HRD) per drawing 7790189. A receiver core hardness of 35 HRC is the optimum value.

Development of Magnetic Particle Inspection

According to an American Society of Nondestructive Testing Level III certified individual who audits U. S. DOD aerospace parts contractors for compliance with government specifications, the procedure for magnetic particle inspection has changed since the late 1950s. Regarding the M14 receiver blueprint, he states [minor spelling errors corrected]:
The listed procedure would only detect flaws oriented in the transverse direction of the receiver. On a forged or billet receiver, it would only detect flaws perpendicular to the grain flow of the metal. Most often, flaws will run in the direction of grain flow, not perpendicular to it. If the receiver was made from a casting, the procedure would, at best, only detect 50% of the possible flaws.

The amperage values listed are also below the requirements of MIL-STD-1949A and ASTM E 1444. The formula for determining coil shot requirements in the coil described is: NI = 45000/(L/D), where I is the required amperage, N is the number of turns in the coil, L is the length of the part, and D is the diameter (or major outside dimension). However, L/D (called the length to diameter ratio) can never exceed 15. If L/D exceeds 15, then 15 must be substituted for L/D. What this means is, when working the formula, the applied amperage through a five-turn coil should never be less than 600 Amps. The length to diameter ratio can never exceed 15, if it does, then 15 must be used. It is impossible to use the prescribed formula and come up with 400 to 500 Amps and by today's standards, the proper inspection might include a couple of coil shots (by shots I mean applications of electric current) plus a couple of direct contact shots and probably a central conductor shot. Any qualified magnetic particle inspector would most probably look at an M14 receiver and say at least two shots were required, and possibly as many as five. If I were inspecting it for myself, I would say five shots.

Disclaimer: The above information is for educational purposes. Machining, heat treat or inspection of any firearm receiver or frame should be performed by an experienced firearm manufacturing FFL / SOT. The author is not responsible for any consequence resulting from any attempt by anyone to manufacture, heat treat or inspect a firearm or parts thereof. Such activities should only be performed by businesses licensed and credentialed to do so.

USGI Receiver Geometry

Comparison of Select Fire and Semi-Automatic Receivers - The functional differences between USGI and commercial M14 type semi-automatic receivers are slight but important. The USGI M14 receiver has a notch cut in the center of the receiver rail. This allows for dismounting of the operating rod during disassembly and fore and aft movement of the connector assembly during full automatic fire. The forward end of the USGI receiver rail has a groove cut into it on the underside to allow the front end of the connector assembly to slide back and forth and secure the connector from drifting to the right and losing contact with the operating rod as it moves forward to initiate automatic firing sear release function. The USGI receiver is also manufactured with a selector lug on the rear right hand bottom side. The selector and connector assemblies are attached to the rifle by this selector lug.

Receiver Barrel Ring – USGI receivers have a distinct machined flat surface with a longitudinal edge on the top of the barrel ring.

Caliber Marking - Springfield Armory, Winchester, Harrington & Richardson and TRW used the upper case letters MM to denote millimeter in their receiver heel stampings.

Manufacturing Difficulty and Forgiveness – Even though the M14 receiver is essentially an updated 1936 design, it is not easily machined into final form. As of 2004, a five axis CNC machining center is still not capable of performing all of the cuts necessary to bring the receiver to final form. Some cuts still require manual manipulation of a cutting tool to complete the form to blueprint specification. However, it is a very forgiving design in that many of the manual operation machining cuts are purely cosmetic.

Forming of Military Receivers

USGI and Taiwanese receivers are drop forged. The raw receivers were formed by the impression-die drop forging method. The flashing was removed and the finish machining completed on special broaching, milling and drilling machines. A Worcester, MA based subcontractor specializing in forgings made the M1 o and M14 receiver and component forgings for Harrington & Richardson. Wyman & Gordon Co. is likely the subcontractor but this has not been confirmed with the company. Wyman Gordon was the only forging plant in the vicinity of Harrington & Richardson in the 1950s and 1960s. The Wyman & Gordon plant was located within two miles of the Harrington & Richardson Main Plant on Park Avenue in Worcester, MA. The H&R, Springfield Armory and Winchester receivers would last 400,000 rounds and the TRW receivers were good for 450,000 rounds. 1

M14 Rifle Factory Inspection

The following describes the requirements each M14 rifle had to pass before it could be shipped to the military. The M14 rifle was tested by first firing a high pressure proof round. That was followed by function tests in semi-automatic, burst automatic, and sustained automatic fire. The rate of fire in automatic had to be within a specified, narrow range. Each rifle was required to deliver its center of impact within a specified limited area around the point of aim at 100 yards with the rear sight set at eight clicks up from bottom and at zero windage. Every rifle had to group within 5.6 " at 100 yards with five rounds of M80 ball ammunition. If the rifle failed, it was tagged to record what the particular problems were. The manufacturer replaced the parts and sent it through the entire inspection process again. Most rifles passed the testing the second time around. The information noted on the tags was recorded and used to analyze the manufacturing process to determine what needed correction.

In addition to test firing, which every rifle went through, M14 rifles were pulled out at given intervals and subjected to endurance firing for 6000 rounds. Only a small fraction of any kind of failure was allowed in the endurance test. Some of the M14 rifles completed the 6000 round endurance with no malfunctions. While a five shot group of 5.6 " at 100 yards may not seem terribly accurate this includes the inaccuracy of the M80 ball ammunition factored in. The Boston Ordnance District was responsible for final acceptance of M14 rifles manufactured by Harrington & Richardson and Winchester. By Fiscal Year 1962, it had conducted a study into the factory accuracy testing rejection rate of M14 rifles. 2 The Boston Ordnance District discovered that the M80 ball ammunition of itself had an average spread of 3.57 " at 100 yards within every ninety rounds fired. Ammunition inconsistency aside, a rack grade M14 type rifle is accurate for a battle rifle when properly assembled.

After completion of all firing tests, each bolt assembly was examined by magnetic particle inspection for cracks, seams and other injurious defects. If the bolt passed examination, the bolt was marked with the letter M. The bolt assembly was then cleaned, the roller repacked with grease and the rifle reassembled.

M14 Production at Springfield Armory

The Springfield Armory was built during the American Revolutionary War. From 1794 to 1968 it was the center of military small arms development and production in the United States. The armory tested and manufactured several muskets in the eighteenth and nineteenth centuries for the U. S. Army. It also produced the Krag-Jorgenson, M1903 and M1 Garand rifles prior to the M14 project. Springfield Armory was closed on April 30, 1968. The site was reopened as the Springfield Armory National Historic Site in 1978 under the operation of the U. S. Department of Interior National Park Service. It houses the largest firearms collection in the United States and the second largest in the world.

Springfield Armory was the first of four M14 rifle manufacturers for the U. S. government. It was tasked with setting up a pilot production line in April, 1958. Startup of parts production began in December, 1958. The first five parts made were the receiver, the bolt, the gas cylinder, the operating rod handle and the trigger housing. Troublesome production issues included obtaining satisfactory precision castings for the flash suppressors, proper welding techniques for the operating rods, and achieving satisfactory heat treatment for the receivers. The first M14 rifles were delivered to the U. S. Army in August, 1959. M14 production orders followed in November, 1959, March, 1961, and Fiscal Year 1962 with a M14 NM run in Fiscal Year 1963.

The M14 operating rod blueprint requires a weld near the aft end of the cylindrical portion. Springfield Armory (and Winchester and Harrington & Richardson) made operating rods from two pieces of steel. It had 400 of 3100 employees involved with the M14 rifle in August, 1961. Springfield Armory made the least number of USGI M14 rifles.

Springfield Armory Machine Tools - The following describes some of the machine tools in use by Springfield Armory in August, 1961:

1. The barrel installation machine screwed the barrel and receiver together with the exact prescribed torque in seconds

2. Broaching machines were used for high speed removal of metal from the receiver forging

3. A grinder was used to grind the rear faces of the M14 bolt lugs

M14 Production at Winchester

Oliver F. Winchester began his business venture into firearms in 1855. Eleven years later, he founded the Winchester Repeating Arms Company in New Haven, CT. He manufactured the first successful repeating rifle in the world in 1866. By 1872, Winchester was begins making ammunition. In 1931, Olin Industries purchases Winchester Repeating Arms Company and combines it with the Western Cartridge Company to form Winchester-Western. During World War II, Winchester-Western manufactured M1 Garand rifles. In 1954, Olin Industries and Mathieson Chemical Corporation merge to form the Olin Mathieson Chemical Corporation. Its name was simplified to Olin Corporation in 1969. In 1981, the shotgun and rifle manufacturing operation is sold to U. S. Repeating Arms Company, Inc. Today, U. S. Repeating Arms continues the tradition of manufacturing quality shotguns and bolt and lever action rifles under a licensing agreement from the Olin Corporation. The Winchester named operation remains a leading manufacturer of ammunition. The ammunition is produced at facilities in East Alton, IL and Geelong, Australia.

In February, 1959, Winchester was the first of three commercial firms to be awarded a M14 rifle contract. Subsequent M14 contracts were awarded April, 1960 and Fiscal Years 1962 and 1963. Winchester designed special machinery to make the M14 receivers and wood stocks. Winchester was delayed several months getting the bugs worked out of the receiver making machine tools but were successful in meeting its required monthly production rate by August, 1961. The automated high speed woodworking machinery was successful from the beginning of operation. Winchester produced the second largest number of USGI M14 rifles.

Winchester Machine Tools – The following describes some of the machine tools used by Winchester in August, 1961 to produce the M14 rifle:

1. The barrel drilling installation consisted of eight machines of six spindles each for drilling barrel bores.

2. The Gorton straight-line transfer machines performed thirty-two high precision machining operations on the receiver automatically.

3. The sixteen station stock inletting machine replaced sixteen single purpose woodworking machines in making wood stocks.

Winchester Production Differences – Receivers were machined using special milling machines. The other three rifle manufacturers formed their receivers by extensive broaching. Winchester had the most automated stock making machinery of the four manufacturers.

M14 Production at Harrington & Richardson

Harrington & Richardson began manufacturing firearms in 1874 and produced double action revolvers as early as the 1880s. Through the years Harrington & Richardson produced reliable and affordable rifles and revolvers. The company produced the M1 Garand rifle from 1952 to 1956 for the U. S. Government. Harrington & Richardson M1 Garand rifles are sought after by collectors. Production at Harrington & Richardson ceased in 1986.

Harrington & Richardson received its first M14 contract in April, 1959. Subsequent contracts were awarded in February, 1960, September, 1961, in Fiscal Year 1962, and then again in Fiscal Year 1964. In August, 1961 there were about 1000 employees working on the M14 project at Harrington & Richardson in Worcester, MA. Harrington & Richardson produced the largest number of USGI M14 rifles.

H&R Machine Tools – The following describes some of the machine tools used by Harrington & Richardson in August, 1961:

1. The Cincinnati special milling machine was a multi-station mill for finish machining operations on the receiver.

2. The crush grinder was used to grind gas cylinder threads on the M14 barrel.

Harrington & Richardson Parts Failures – One H&R receiver and two HRL bolts failed during range firing at Fort Benning, GA in mid-December, 1960. The fractured receiver was made of the incorrect material, AISI 1330 steel, instead of AISI 8620 steel. This was an unintentional mishap on the part of Harrington & Richardson. When the receivers made of the incorrect steel were heat treated the result was unsafe. These AISI 1330 steel receivers were weak and brittle. The incorrect steel had been used for several days of production of receivers.

One bolt had a sheared right lug and the other one had cracked lugs visible to the naked eye. Bolts that failed were made by one subcontractor and marked HRL. A thorough metallurgical investigation was performed by government and Armour Research Foundation metallurgists. The failed bolts were cut into sections and examined using microscope photography. The major fault was the failure to strictly adhere to the written heat treatment procedure even though the correct steel was used. The procedure requires the bolts to be heated to a narrow temperature range then immediately cooled by oil immersion. If the bolts are not brought up to the required temperature or if they are allowed to cool before oil quenching, an excessive amount of free ferrite is formed. Ferrite is soft and weak iron. Ferrite does not bond with carbon atoms so the freed up carbon atoms moved into the rest of the bolt. This condition in the HRL bolts created a very hard and brittle martensite molecular structure. Under repeated impact loading, cracks formed and grew in the lugs, resulting in catastrophic bolt failure.

A task force was formed to determine the cause of failure and to implement a plan of action to prevent any more failures of this kind. Springfield Armory test rifle bolts which had gone thousands of rounds were examined for similarities and differences with the failed HRL bolts. The test rifle bolts demonstrated that minor cracks may start in the hardened surface but they do not grow through the bolt core if the heat treatment is correctly performed. Properly heat treated bolts were found generally to have less than 10 % free ferrite but the failed bolts had as much as 50 % free ferrite. The end result was additional quality assurance provisions as required by Ordnance Weapons Command Engineering Order No. 164 released on January 11, 1961. These new requirements included a revised inspection procedure, installation of new heat treatment equipment and a magnetic analyzer to check receiver material at the Harrington & Richardson plant. The revised inspection procedure included two separate magnaflux inspections of each receiver, before and after heat treatment. The magnetic analyzer was developed by Springfield Armory with assistance from Watertown Arsenal.

M14 Production at TRW

Thompson-Ramo-Wooldridge, Inc. was the fourth and last of the USGI M14 rifle manufacturers. It is referred to as TRW throughout this work. The earliest origin of TRW was in the 1901 founding of the Cleveland Cap Screw Company. Eventually, this business was named Thompson Products. Thompson Products was a manufacturer of automobile and aircraft engine parts. In 1958, Thompson Products merged with Ramo-Wooldridge to form Thompson-Ramo-Wooldridge Corporation. Ramo-Wooldridge, Inc. had been created in Los Angeles, CA in 1953 by Dr. Simon Ramo and Dr. Dean Wooldridge. The five major business groups of TRW in 1962 were Automotive, Electro-Mechanical, Electronics, Space Technologies Laboratories and TRW International. The corporate name was changed to TRW, Inc. in 1965. In 1999, TRW Automotive bought the British aerospace and automotive parts manufacturer LucasVarity. In December, 2002, its defense business was purchased by Northrop Grumman. The automotive portion of the business became a separate company for a short time but was then bought by The Blackstone Group. Goodrich Corporation took over the TRW aerospace business.

TRW received its first M14 contract in October, 1961. The second M14 contract was let in October, 1962 and a M14 NM contract in Fiscal Year 1965. In late 1961 and the first half of 1962, its Cleveland, OH plant was remodeled and set up for M14 production. This plant was known as the Ordnance Works of the Electro-Mechanical Group within TRW. TRW manufactured the third largest number of USGI M14 rifles. The TRW M14 manufacturing operation is briefly described.

As described below, TRW used several manufacturing techniques not shared with other manufacturers.

The principal stages of TRW M14 receiver manufacture were: 1) steel slug cut off from bar stock 2) drop forging after warm size 3) chain broaching and qualification broaching 4) machining through three dimensional mills 5) additional broaching and 6) phosphate coating.

The principal stages of TRW M14 bolt manufacture were: 1) cut off steel slug 2) extrusion 3) warm-coining 4) thirty machining operations on the Krueger lateral transfer machine 5) ten machining operations on two five station special milling machines and 6) phosphate coating.

The principal stages of TRW M14 operating rod manufacture - 1) cut off steel slug 2) bump up and roll 3) warm sizing 4) finish machining and 5) phosphate coating. Note that TRW made one piece operating rods.

TRW Machine Tools - The following describes some of the machine tools in use by TRW in November, 1962:

1. The Allen multi-station drilling machine drilled all the small holes in the receiver.

2. The bolt assembly fixture completely assembled the bolt except for the roller.

3. The Colonial fifteen station pull-type broach cut the receiver magazine slot.

4. The Footburt 144 " chain broach was used for the first stage in receiver machining.

5. The Krueger lateral transfer machine performed thirty machining operations on two bolts at the same time including precision boring, reaming, gun drilling, hollow milling, and automatic gauging and inspection.

6. The Seneca Falls tracer lathe completed barrel exterior contour turning in two passes.

The TRW Mystique

TRW rifles and parts have a long-standing reputation as better made than those from the other three M14 manufacturers. This was obvious as early as late 1962, from objective facts described below. The first TRW rifles were delivered in October, 1962, one month ahead of schedule. TRW’s production record and the quality of its rifles brought enthusiastic praise from the Department of Defense and from the press. TRW was ahead of Winchester and Harrington & Richardson in a number of ways. Because of its background, TRW had a broader and more sophisticated production experience. TRW considered itself to be highly skilled in the manufacturing techniques of precision forging and chain broaching. TRW made only made eleven parts during its M14 rifle production. These eleven parts (rear sight base, receiver, trigger housing, hammer, bolt, operating rod, barrel, connector, gas piston, gas cylinder, and flash suppressor) amounted to a little less than 65 % of the cost to the government. TRW also made trigger group safeties. TRW safeties were marked in two lines with T R W on top and H T – B below. TRW M14 safeties are likely replacement parts made after rifle production.

The expertise of TRW is borne out by the 1962 American Rifleman interview of S. C. Pace, Electro-Mechanical Group Vice President. Mr. Pace explained how TRW’s personnel applied its jet engine manufacturing experience to the production of M14 rifles. TRW settled on making what parts it could make economically well (based on its expertise), and subcontracted out the remaining parts which were easily manufactured from conventional methods. TRW made one piece operating rods. Barrel interiors were formed by German design hammer forging. Barrel exterior contours were formed in two turning passes by using a Seneca Falls tracer lathe. The Seneca Falls tracer lathe replaced six conventional machine tools. The same barrel operation required four turning passes at Winchester. The TRW automatic barrel installation machine was similar to the other makers but it had some changes based on the experiences of the other manufacturers. As previously mentioned, TRW receivers gave about 6 % longer service life than others. TRW did assemble, test and ship all completed M14 rifles stamped with its logo on the receiver heel. Later on, TRW became the only commercial contractor to ever produce the USGI M14 NM rifle.

The M14 failure rate was 5 % to 12 % from all causes among Springfield Armory, Winchester and Harrington & Richardson as of August, 1961. TRW had assembled and tested its first M14 rifle in August, 1962. By November, 1962 TRW M14 production was 100 per day and it had had no rejections to date. The largest five shot group of any TRW rifle up to November, 1961 was 5.5 “ out of a maximum allowable 6.1 “ at 100 meters. The average five shot group size for TRW rifles until November, 1962 was 2.5 “ to 3.0 “ in factory testing.

With very few exceptions, e.g., Winchester barrels in its second contract, all four manufacturers were required to use the same material and meet the same specifications in making M14 rifles. The TRW mystique is further strengthened by the growing pains suffered by Winchester and Harrington & Richardson in 1960 and 1961. Overall, it is fair to say that TRW had the most trouble-free production record of the four manufacturers. Sometimes it pays to be last but it always pays to plan well.

The author has wondered whatever became of the M14 project machine tools operated by TRW. No information has been available but Other Source # 27 has offered the best explanation to date. In his opinion, the TRW machine tools were sold off piecemeal after production had ended and they had fully depreciated.



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