[SIZE="3"][B]Report of the M16 Rifle Review Panel. Volume 5, Appendix 4. Ammunition Development Program[/B]
Primer Sensitivity
Initial Specifications. Ammunition specifications established by the Air Force on 24 January 1963 provided for quality control against cocked, inverted, loose, and nicked primers. The specifications further provided for inspection and test of waterproofing
and the crimp of primers. However, the specifications did not provide for specific limitations on primer sensitivity for 5.56mm ammunition.-
Development. At the first meeting of the Technical Coordinating Committee on 26 March 1963,16 / the Air Force representatives submitted a list of reported ammunition deficiencies, which included "high primers" and "primers too sensitive". It was agreed that Frankford Arsenal would investigate the matter and recommend corrective action.
One of the malfunctions reported by the Air Force was the premature firing of cartridges that occurred upon initial charging of the M16 rifle with a cartridge from the magazine, or upon singleloading of a cartridge directly into the chamber, or when two rounds were fired at one trigger pull during semiautomatic fire.
This malfunction was attributed to "high" or protruding primers, although the tests did not confirm this theory..
However, analysis indicates that if high primers caused the premature firing, the firing should have occurred upon impact of the bolt face with the protruding primer. At this point in the weapon cycle, the bolt head would not. have been rotated to the locked position by action of the cam pin and carrier. Had firing occurred with the bolt in the unlocked position, it would have resulted in a blow back and would not have been undetected. No such disruptions were reported-. Since premature firing occurred after bolt-locking, it must have coincided in time with the impact of the bolt carrier against the bolt head. At the instant of impact, the "free floating" firing pin is moving at the velocity
of the bolt carrier. The kinetic energy of the pin must be dissipated by such frictional forces as it encounters in the forward movement, and, finally, in impact of the firing pin tip with the primer of the chambered cartridge. This premise was confirmed by
the visible indentation appearing on cartridges which were chambered by the mechanism and extracted unfired.
Frankford Arsenal identified test procedures for measuring firing pin energy and recommended limits for primer sensitivity.
These procedures were designed to measure the indent depth of the firing pin upon the primer cup. Tests are conducted by dropping steel balls of known weights from various measured heights upon a device containing a firing pin and a primed case assembly.
Using this procedure and measuring the energy in inch-ounces, Frankford Arsenal was able to develop test data upon which to recommend a lower limit of "none-to-fire" and an upper limit of "all-to-fire".
It recommended that primers be manufactured so that the none-to-fire limit should be not less than 16 inch-ounces of energy and the all-to-fire limit should be not greater than 64 inch-ounces of energy.
A meeting of the Technical Coordinating Committee was held at Hill Air Force Base 5 June 1963, at which time a difference of opinion arose as to primer sensitivity. The purpose of the meeting was to establish procedures for transfer of the Air Force technical data to Frankford Arsenal for use in the FY 1964 procurement and to insure that there would be no unnecessary duplication of effort in completing the Army technical data package. The Air Force explained at the meeting that it could not release technical data to the Army earlier than 29 May 1963 because it was necessary to withhold data
while the Air Force purchase was processed through pre-procurement channels.
These data became available to the Army 29 -May 1963. 1963 meeting, the Army Project Manager directed that Frankford Arsenal and Hill Air Force Base take joint action to resolve differences in firing pin energy and primer sensitivity. This joint action included test firing at Lackland Air Force Base during the week of 22 July 1963.1 91 Frankford Arsenal presented the results of the joint study to the Technical Coordinating Committee on 13-14 August. The committee agreed to a none-to-fire limit of 12 inch-ounces and an all-to-fire limit of 48 inch-ounces, with an understanding that if tighter limits could be met, consideration would be given to tightening these limits at a later time. The Army Staff representative (from the Assistant Chief of Staff for Force Development) withheld concurrence on these limits pending further evaluation by the Army Staff.
On 17 September 1963, the Army Staff informed the Project Manager that the primer sensitivity limits contained in the specifications could not be accepted because of the risk of inadvertent fire. The Commanding General, USAMC, stated that the only practical solution was to modify the weapon. As a result of the Army action, USAMUCOM was directed to suspend procurement of one million rounds of 5.56mm M193 ball cartridges for the Army2 2/ until the problem was resolved. Solicitation of bids for the balance of FY 1964 Army and FY 1964 U.S. Air Force orders were held in abeyance. In the meantime, on 3 September 1963, the Ammunition Procurement and Supply Agency (APSA) was advised that Olin-Mathieson and Remington, the only two eligible bidders for production of 5.56mm ammunition, had both taken exception to the technical data package. Both companies recommended changes to the primer sensitivity requirements. A meeting was held at Frankford Arsenal on 5 September 1963 with representatives from USAMCOM, APSA, and the two producers to resolve these disagreements. As a result of this meeting, Frankford Arsenal developed supplementary changes in primer sensitivity requirements in the technical data package. The requirement was established at a minimum of 12 inch-ounces and a maximum of 48 inch-ounces. As previously stated, however, on 17 September 1963, procurement would be suspended until the overall problem could be resolved.
Remington Arms Company, on the basis of the information contained in the Frankford Arsenal First Memo Report, undertook the design of a new primer that would be less sensitive and less susceptible to the inadvertent energy delivered to the primer by the free-floating firing pin of the AR15 rifle. Since it is difficult to adjust primer sensitivity by chemical changes, Remington elected to accomplish the desensitization" by increasing the mechanical strength of the brass primer cup, which must be indented by the firing pin to cause ignition.
As a result of the decision of the Commanding General, USAIIC, to modify the rifle, Colt's Inc. developed two designs, a linear spring device and a cam pin friction device, to reduce firing pin energy on bolt closure. These two designs were tested by the Air Force conclusions of this test were that both devices effectively reduced firing pin energy; however, the Air Force recommended against their adoption because they increased the probability of a misfire (although no failures to fire were identified in the test results), added to the cost of the weapon, and adversely affected its reliability. Army tests of these devices indicated that the linear - ~spring friction device was a satisfactory solution; however, at the Technical Coordinating Committee meeting of 10 December 1963, at which a comparison of all tests done by the Army, Air Force, and Colt's Inc. was made, the committee agreed to adopt a modified lighter firing pin, which was used in the cam friction device and was recommended by Colt's as a solution to the problem. The committee also agreed to accept printer sensitivity criterion of none-to-fire limit of 12 inch-ounces and an all-to-fire limit of 48 inch-ounces. The committee recommendation was forwarded through the Army Staff to the Office of the Secretary of Defense and approved 23 December 1963..8/ Thus, two system changes were initiated to correct the primer sensitivity specifications proposed by the joint study in which the Army could not concur.
The Commanding Officer, Frankford Arsenal,29/ suggested to the project manager that further consideration be given to modifying the M16 rifle in order to allow a wider range of primer sensitivity without an increase in the user's risk of either accidental firing or misfire. Rationale for this recommendation was based on production experience with 5.56mm M193 ball ammunition which indicated that specified primer sensitivity limits were difficult to meet. There had been delays in production and deliveries attributable in part to the difficulty of primer manufacture within the prescribed limits. Manufacturers had contended that any appreciable acceleration in production schedules would aggravate this problem. Frankford Arsenal again stated its position, recommending weapon modification.
The Technical Coordinating Committee reviewed the propriety of the primer sensitivity limits on 3 June 1965.2 Dta on about 400 primer lots produced in accordance with the adopted specifications indicated that production difficulty had not been so great as had been predicted by private industry or by Frankford Arsenal.
The primer sensitivity limits were about as tight as possible for mass production. A rejection rate of about 3 to 5 percent (depending on the producer) for primer production was indicated, but the rejection rate was not considered excessive for a relatively I inexpensive component. The committee noted that no problems with either inadvertent firing or misfire had been experienced or reported. The committee did not make any recommendations to change the primer sensitivity limits, but did note that any future weapon designs in 5.56mm caliber must accommodate these limits.
A report by Headquarters, United States Army Combat Developments Command Experimentation Command (USACDCEC), of the field experimentation phase of the Small Arms Weapons System (SAWS) Study, identified low primer sensitivity in 5.56mm ammunition as one of the major causes of 5.56mm weapons malfunctions.
Analysis by USACDCEC of data accumulated during the experiment indicates that in 1,261,215 rounds fired by the 5.56mm weapons, there were no instances of cartridges firing when the bolt was closed without pulling the trigger and no cases where the primer indentations of misfire cartridges were sufficiently shallow to have caused misfires. Misfires were not due to high primer sensitivity but to low primer sensitivity. They occurred in all five models of 5.56mm weapons being tested. Some of the misfires with the Stoner machine gun were attributed to a lack of sufficient recoil power. The four weapons other than the Stoner machine gun had 829 misfires in 1,008,629 rounds fired, or one per 1,217 rounds. The analysis of results of SAWS Engineering and Service Tests conducted by the U.S. Army Test and Evaluation Command determined that primer sensitivity of the 5.56mm cartridge was an area requiring further investigation, since failure to fire was the most frequent malfunction with all 5.56mm weapons.
Primer Composition
Initial Specifications. Ammunition specifications established by the Air Force 24 January 1963 did not restrict the chemical composition of primers to be used in 5.56mm ammunition.
Development Efforts.
Colt's Inc., first experienced difficulty in 1963 in complying with the 6,000-round endurance test for the Air Force contract.- / Specifically, the problem was defined by Colt's as an excessive accumulation of fouling on the bolt assembly. This fouling resulted in sluggish operation, which in turn, lead
to failures to feed and eject. Frankford Arsenal was assigned the task of investigating the problem and determining to what extent the trouble was attributable to the ammunition used. In the course of the investigation, it was determined that these rifle lots which failed the endurance test were those firing Remington ammunition and using a Remington 721M Primer, which contains lead styphrate, barium nitrate, tetracene, antimony sulfide, and calcium silicide. Those rifle lots that passed the endurance test had fired ammunition using a Remington 92 Primer, which differed from the 72M Primer Ii in that it did not contain antimony sulfide and calcium silicide.
In view of the possibility that the primer might have contributed to the excessive fouling problem, and until standardization of a primer-propellant combination could be accomplished, Frankford Arsenal recommended that a satisfactory discriminative fouling test be required as a criterion for 5.56mm cartridge acceptance. An approved change 3 5 / required that a 1,000-round fouling test be successfully conducted on each pre-production lot of ammunition and on any subsequent change in primer ingredients by the producer as a condition of acceptance. This change was incorporated into the technical data package for the fiscal year 1965 procurement program.
At the 3-4 June 1965 Technical Coordinating Committee Meeting,-6
the Colt's Inc. representative reported that ammunition recently
provided for the endurance test was causing more fouling than
the ammunition previously used. The Project Manager directed
Frankford Arsenal to conduct a primer chemical analysis to determine
whether a producer had made an unauthorized change in primers.
Frankford Arsenal reported that its analysis had revealed no change
in primer composition and that the primers were acceptable.
Further analysis of the chemical composition of primers by
Frankford Arsenal resulted in a change in the military specification
on 8 February 1966 to eliminate calcium silicide as an acceptable
compound because it was a contributor to excessive fouling. [/SIZE]