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Magnectic particle inspection, a way to examine the bolt for defects after proof fireing.
 

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Discussion Starter #3
Done by the manufacturer? They just etch the M by hand instead of stamping? Thanks for the quick response!
 

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Yes. It also tells you it has never been refinished.
 

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In theory, magnetic particle inspection (MPI) is a relatively simple concept. It can be considered as a combination of two nondestructive testing methods: magnetic flux leakage testing and visual testing.

I think the dod had this done after H&R and winchester had a batch of bad bolt w/ wrong alloy steel.. had some bolts blow up. Used magnetic comp to find the bad alloy..marked the bolts after testing.. B2B
 

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I think the dod had this done after H&R and winchester had a batch of bad bolt w/ wrong alloy steel.. had some bolts blow up. Used magnetic comp to find the bad alloy..marked the bolts after testing.. B2B
This is pure speculation on your part. MPI can not find a bad alloy, it can simply find stress factures or cracks in a metal.

Yes H&R did have a problem with an early batch of bolts due to wrong heat treatment. Don't know if there were steel issues involved.
Member Different could give us the specifics.
 

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Electro Pencil

The reason the bolt was not stamped with the M is because it has had the surface hardened. The electro pencil marking was used to prevent damage to the bolt.
 

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Not speculation, from what I've read, the issue was a steel suppler delivered the wrong alloy steel to Winchester and or H&R, the bolts failed in testing or on proof firing etc.. DOD ordered bolt inspection both MPI and a magnetic field testing which by using a bolt of a known alloy ie. the right alloy steel, placing the suspect bolt in the mag fiels could compare the two bolts and detect the different metal alloy, and the bolt could be destroyed..and taken out of service with out any destructive testing and very little cost..time etc.. I believe the bolts wer marked with a M after passing MPI and alloy tests.. B2B
 

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There were 4 bolts that failed. All 4 were found to be manufactured of the correct alloy. Improper heat treatment was found to be the cause of the failure.

8 H&R receivers were produced from the wrong alloy
(AISI 1330). These were destroyed.

Information from Lee Emerson, M14 Rifle History and Developement.
 

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Was this bad batch -

A one-time, short-term incident? I see a good number of bolts electro-penciled 'M', & I am noticing quite a few w/o the marking. Was MPI the rule, or the exception?

Much obliged,
Matt
 

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Was this bad batch -

A one-time, short-term incident? I see a good number of bolts electro-penciled 'M', & I am noticing quite a few w/o the marking. Was MPI the rule, or the exception?
From M14 Rifle History and Development Fifth Edition:

"Receiver and Bolt Failures – Two receivers, serial numbers 19478 and 19656, and four bolts from three manufacturers failed during range firing at Fort Benning, GA in December 1960. Later that month, receiver serial number 73293 fractured during proof firing at the Harrington & Richardson factory in Worcester, MA. The bolt in rifle serial number 73293 suffered abnormal peening on the bottom of the right hand lug and severe indentation on the face of the left lug. Receiver serial numbers 19478 and 73293 were made of incorrect material, AISI 1330 steel, instead of AISI 8620 steel. Receiver serial number 19478 was stamped Winchester but it was one of 850 M14 receivers Winchester had purchased from Harrington & Richardson for initial production. Receiver serial numbers 19478 and 73293 each failed completely in both sides just forward of the receiver lugs.

Subsequent testing of 554 Harrington & Richardson receivers in January 1961 found eight more made from AISI 1330 steel and one made of 4 % nickel alloy steel. The serial numbers of Harrington & Richardson M14 receivers found through testing to be made of AISI 1330 carbon steel were: 69121, 71244, 71927, 71974, 72929, 73761, 74238 and 74486. The high nickel alloy steel receiver serial number was 71408.

The use of the wrong material 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 receivers made of the improper material were destroyed but Harrington & Richardson had to produce the contracted number of receivers. It is not known if the serial numbers from the defective receivers were reused or if new serial numbers were issued for the replacement receivers.

One of the four bolts to fail at Fort Benning was from rifle serial number 19453. It had a completely sheared right lug and a severely cracked left lug. The failed bolt was made by Textile Machine Works, a subcontractor to Harrington & Richardson. A thorough metallurgical investigation of the M14 bolt was performed by government, Ipsen Furnace Company and Armour Research Foundation metallurgists between January and May 1961. The failed bolt was 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 HRT bolt created a very hard and brittle martensite molecular structure. Under repeated impact loading from the rifle being shot, cracks formed and grew in the lugs, resulting in catastrophic bolt failure.

A task force of about forty Army Ordnance Command representatives met on December 28 and 29, 1960 to determine the causes of failure and to implement a plan of action to prevent any more such failures. After the meeting, a combined team from Springfield Armory and Boston Ordnance District visited the following contractors and subcontractors to review M14 component manufacturing procedures and obtain samples for evaluation: Winchester in New Haven, the Rochdale and Worcester H&R plants, Storms Drop Forge, and Textile Machine Works. The following deficiencies were noted by the team:

1) M14 bolts at the Winchester plant were not quenched according to good engineering practice for 8620 steel. Additionally, there was no magnetic particle inspection of Winchester M14 bolts after proof firing.

2) Receivers that missed steps in the machining process were reworked by spot annealing and hand grinding at Harrington & Richardson.

3) Winchester was unable to meet the minimum core hardness limit for bolt heat treatment.

4) Textile Machine Works was unable to meet the maximum core hardness limit for bolt heat treatment."

and

"Springfield Armory test rifle bolts which had gone thousands of rounds were examined for similarities and differences with the failed HRT bolt. 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 bolt from receiver serial number 19453 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. This Engineering Order applied to the first and second Winchester contracts and the first Harrington & Richardson contract. These new requirements included a revised inspection procedure for the barrel, bolt and receiver, installation of new heat treatment equipment and a magnetic analyzer to check receiver material. The revised inspection procedure included two separate magnetic particle inspections of each receiver and bolt, before and after heat treatment. The magnetic analyzer was developed by Springfield Armory with assistance from Watertown Arsenal.

On April 23, 1961, Ordnance Weapons Command issued instructions to Raritan Arsenal to inspect, segregate and reassemble approximately 35,000 Harrington & Richardson and 850 Winchester M14 rifles manufactured before the issuance of Engineering Order No. 164. The instructions required inspection of the barrels, bolts and receivers for compliance with material, hardness and dimension specifications. Springfield Armory provided technical assistance, training and inspection equipment for this work at Raritan Arsenal. The relevant portion of the May 08, 1961 Springfield Armory report is reproduced here:

“Regarding cracks in bolt locking lugs, numerous firing tests at Springfield Armory have proved minute cracks in bolt lugs do not cause early failure if metallurgical structure of bolts is correct and bolts and receivers are dimensionally correct.

On 23 April 1961, instructions were issued from Hq. OWC on the inspection criteria to be observed at Raritan Arsenal for the inspection segregation and reassembly of M14 rifles. The instructions are as follows:

After careful evaluation of available tests and performance data, and with due consideration to the urgent requirements for M14 rifles, the following are effective immediately:

(a) M14 bolts manufactured prior to the implementation of OWC EO 164 except HRT lots A01 and A1980, and those 850 OMCC bolts in weapons at Raritan Arsenal returned from the field are acceptable for immediate assembly provided the following 100 % reinspection is conducted:

(1) Check for compliance with surface hardness requirements.
(2) Inspect for cracks at lug area using 600 amperage on Magnaglow inspection. No cracks are permissible
(3) Inspect for compliance with the 0.028 minus .008 radius and toll marks in lug area in 4 locations.
(4) These bolts will not be used for repair parts.
(5) All bolts in the above category will be marked or etched below the part number or serial number with a small identifiable star or asterisk.

(b) Receivers meeting all other contract requirements are 100% acceptable provided inspection is conducted to insure:

(1) Compliance with specified surface hardness requirements.
(2) That proper steel was used in manufacture as determined by use of a magnetic analysis comparator. Receivers exceeding plus 40 reading shall be rejected. Receivers exceeding minus 40 may be accepted but will be marked or etched with a small identifiable star or asterisk.

(c) Dimensional requirements for both components remain unchanged.

(d) Boston Ordnance District was authorized to approve RDA’s for bolts meeting the criteria previously stated.

(e) In addition, instructions have been established to accept oversized chambers in weapons at Raritan Arsenal up to .005["] maximum over the drawing tolerance.”

Random sample USGI M14 bolts that had passed all required government inspection and testing measured 52 HRC (HRT marked bolt) and 54 HRC (TRW marked bolt) for surface hardness. Springfield Armory and Winchester carburized M14 bolts by the salt bath method whereas Textile Machine Works used the ammoniated gas method for bolt carburizing.

The bolt is the second hardest part to manufacture on the M14, the receiver being the most challenging. The drawing requirements for the M14 bolt were revised a lot as the M14 project developed. The bolt drawings were originally created in July 1958 and last revised in December 1992 (Revision Y). No other M14 rifle part drawing went through as many revisions.

Due to the bolt failures in late 1960, a lot of research was performed by the U. S. Army into the design and manufacturing process of the M14 bolt. There were bolt failures in five USGI M14 rifles: Harrington & Richardson serial number 73293, Springfield Armory serial number 19656, and Winchester serial numbers 19453, 19478 and 19391.

Three of these bolts had excessive free ferrite but two did not. As a result of the bolt failures, the U. S. Army inspected 33,808 bolts from rifles under serial number 90000. 26,848 of the 33,808 bolts were reused. The inspection tests done on the M14 bolts included magnetic permeability comparisons, measurement of basic magnetic properties, oscilloscope wave form pattern studies, hardness testing, and impact testing at ambient and cold temperatures. The 6,960 bolts pulled from service were due to: 1) surface hardness outside the specification 2) high temper or retemper 3) core hardness greater than 45 HRC 4) core hardness less than 35 HRC 5) core with excessive free ferrite or 6) other unfavorable conditions. The bolts tested had core hardness as high as 46 HRC and as low as 31 HRC. Within a single bolt, it was not unusual to have the core hardness vary up to 4 HRC. Surface hardness was usually within 1 HRC for any point sampled on a given bolt. The bolts sampled ranged from 52 to 62 HRC on the surface.

As of January 1962 (drawing F7790185 Revision H would have been in effect), the heat treat requirements for the M14 bolt were:

Surface - 54 to 59 HRC
Core - 35 to 42 HRC
Case depth - 0.015 " to 0.020 "
Temper temperature - 425 degrees F maximum
Core structure - 10 % free ferrite maximum

With the exception of the five failed bolts from USGI rifles under serial number 75000 and the 6,960 USGI bolts pulled from service, new manufacture USGI M14 bolts have been found acceptable for use by the U. S. Army. USGI M14 bolts made under the final set of heat treatment requirements (drawing F7790185 Revision L and later) were made by Winchester (rifles) and TRW (rifles and spare bolts).

The final heat treatment and hardness requirements for the USGI M14 bolt were established in November 1963:

1) Rockwell hardness readings shall be taken on the top surface of the locking lugs and at the vertical surface of the rear end.

2) Bolt material - 8620H alloy steel except resulphurized content at 0.035 % to 0.50 % that is gun quality specification per ASTM A304, A322, or A331. Hardenability of steel shall be controlled as required to suit manufacturer’s heat treatment process and to assure that the specified mandatory physical properties are met. Austenitic grain size is 5 to 8.

3) Heat treatment recommended process - normalize before machining (oil quenching followed by tempering at not more than 450 degrees Fahrenheit may be used in lieu of air cooling). Carburize at 1550 degrees Fahrenheit to 1600 degrees Fahrenheit to the specified case depth. Without reheating, quench in oil or neutral salt bath from 1500 degrees Fahrenheit to 1600 degrees Fahrenheit. If reheated, quench from 1550 degrees Fahrenheit to 1600 degrees Fahrenheit. Temper to the specified hardness.

4) Heat treating mandatory requirements -
A. Normalize before machining.
B. Carburize to a case depth of 0.012 " to 0.018 ".
C. Temper for one hour minimum at 350 degrees Fahrenheit to 450 degrees Fahrenheit.
D. Core hardness is 33 HRC to 42 HRC. Surface hardness is 66 HRD to 71 HRD (54 HRC to 60 HRC).
E. Microstructure of the core shall not contain more than 10 % free ferrite after heat treatment per AMS 2315.
F. The use of a straight cyanide bath or carbonitriding shall not be permitted.
G. When gas carburizing is used the carbon content shall not exceed 0.84 % at the surface of the bolt per AMS 2762.

A 1961 Watertown Arsenal study of the M14 bolt found its tensile strength to vary, as expected, from 275,000 psi at the case hardened surface to 200,000 psi at the inner edge of the case depth to 138,000 psi in the core. The rear inside corner of the left lug is the point of maximum stress for the M14 bolt when a perfectly machined receiver is mated to a perfectly machined bolt.

The M14 bolt lugs are subject to shear stress when the operating rod pushes the bolt back against the receiver lugs. The bearing surface of the bolt lug and the radius of the inside corner of the rear side of each bolt lug influence the magnitude of stress experienced by the bolt. The rear side of the left bolt lug has a smaller bearing surface than the right side lug so it experiences a higher shear stress.

The sharper, or more perpendicular, the inside corner of the rear side is cut the more severe the stress on the bolt lug. Consequently, the USGI drawing F7790185 specifies a minimum radius of 0.028 " - 0.008 " for the inside corner on the rear side of both bolt lugs. This dimension is absolutely critical to limit the maximum shear stress on the bolt. For example, the Watertown Arsenal study indicates that the maximum shear stress at the left lug rear side inside corner would increase by 28 % (assuming full bearing surface contact) by changing the radius dimension from 0.020 " to 0.011 "."
 

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Interesting in a good way that TRW is never mentioned.

Now I have a real concern: Do current bolts made by SAI, Fulton Armory, LRB and soon to be made SEI, have these kinds of exhaustive tests?

If not, I'm sticking with USGI.
 

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Interesting in a good way that TRW is never mentioned.

Now I have a real concern: Do current bolts made by SAI, Fulton Armory, LRB and soon to be made SEI, have these kinds of exhaustive tests?

If not, I'm sticking with USGI.
You know good and well they don't and can't. Private concerns who manufacture boutique speciality parts for the M14, simply don't have the deep pockets or the where with all of a government arsenal or contractor to apply to the project. I too plan to stick with US GI bolts until the newly manufactured bolts have a decent track record for reliability/durability and meeting the specs.

7th
 

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Do current bolts made by SAI, Fulton Armory, LRB and soon to be made SEI, have these kinds of exhaustive tests?
Commercial bolts can be made very well. However for a commercial manufacturer to stick to the government requirements would put the price in the stratosphere. Imagine if every commercial M1A was produced with the same methods as 1959-63. A rifle would probably go 5-10 times the current pricing.

Example: H&R M14 barrels as posted in the past. This information was given to me by Brookfield, years ago.

Barrels were made in batches of 100. The inspector would randomly spread the barrels into 10 lots of 10. He would take 3 barrels from 3 lots, for a total of 9. The 9 barrels were inspected in high detail like all dimensions and every requirement. If there was a minor error, it could be altered. If there was a significant error in 1 barrel, all 100 were rejected.

Imagine trying to commercially produce a barrel under those requirements.

Remember this before you make fun of the military. These items, unlike most commercial rifles, will be used with a result of either success or death of our troops. When military missions and lives were at stake, cost was never an issue.
 
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