The 5.56 X 45mm “Timeline” – 1972

A Chronology of Development by Daniel E. Watters



The Army National Guard (ARNG) and the US Army Reserve (USAR) receive 129,000 M16A1 rifles.

Rock Island’s Small Arms Systems Laboratory is assigned development of a Firing Port Weapon (FPW) for the XM732 Mechanized Infantry Combat Vehicle (MICV).

Aberdeen discovers that M196 Tracer cartridges loaded with IMR 8208M is clocking lower than normal cyclic rates. WC844 is tested in an experimental batch of tracer, and the cyclic rates return to normal.

Frankford Arsenal conducts a test program to optimize the hardness gradient of the 5.56mm case.

Aberdeen publishes the report “Optimum Bullet Study.” While the use of aerodynamic computations as a design basis for artillery shell has been well established, the information generated had not been on shapes (or in sizes) of obvious interest to the small arms designer. Further work is needed to establish a base of confidence in computing the behavior of small arms projectiles and this should be done in bullet sizes and subject to typical small arms systems constraints. In an effort to provide this more general design basis, several programs are generated within the BRL and later partially supported by other agencies, particularly AMSAA and USASASA.

Frankford Arsenal publishes the report “An Analysis of 5.56mm Aluminum Cartridge Case Burn-Through Phenomenon.” This work was aimed at understanding the “burn-through” problem that has impeded orderly engineering development and application of aluminum alloy cartridge cases in high-performance ammunition since the 1890’s. It has been shown that a gas path through the wall of an aluminum case, and through which propellant gas can flow during the internal ballistic cycle, is a precursor to the “burn-through” phenomenon. Solutions to this problem have been found that either prevent propellant gas flow through a path in the case that develops unintentionally during firing of the ammunition, or alter the effect of propellant gas flow through such a gas path. Since an engineering understanding of the “burn-through” phenomenon is available, work is currently underway to demonstrate the feasibility of aluminum cartridge cases.

The US provides a military assistance grant of 77,417 M16A1, 6,145 M16, 83 XM177-type, and 164 XM148 to South Vietnam.

The US provides a military assistance grant of 70,497 M16A1 to Cambodia.

The US provides 90 M16A1 to Indonesia as part of a military assistance package.

The US provides 24,000 M16A1 and 900 M203 to Jordan as part of a military assistance package. (Deliveries of the M203 stretch through 1973.)

The CDCIA publishes “ASARS II Overview.”

The CDCIA‘s Systems Analysis Group publishes “ASARS II Battle Model: Working Description of Logic.”

RSAF Enfield’s preliminary study concludes. Not surprisingly, the ideal caliber chosen is 5mm, for use with both the IW and LSW. Unconventional technologies such as fléchette and caseless cartridges were deemed too technically difficult to master within the desired time frame. A bullpup configuration is preferred as it gives the desired reduction in size without resorting to folding/collapsible stocks. (The latter design concepts are deemed to lack rigidity, causing accuracy to suffer.) To increase first-shot hit probabilities, the weapons must also be equipped with an optical sight similar to the SUIT. Based on the recommendations, a General Staff Target (GST 3518) is written to give specifications and goals for the following two-year Feasibility Study.

HK introduces a 5.56mm box-fed LMG, the HK 13.

MAS completes ten A2 rifle prototypes.

Mikhail Kalashnikov reportedly receives his first samples of the 5.45x39mm cartridge, and is instructed to develop an AKM variant for the new cartridge.

Cartoucherie de Toulouse experiments with a 4.5x54mm cartridge.

The US Army awards a contract with the Honeywell Corporation’s Ordnance Division (now part of Alliant Techsystems) for the development of a 30mm grenade cartridge to replace the existing 40x46mm. (The actual design is credited to Picatinny.)

Colt Industries recombines the Colt Firearms Division.

Aberdeen publishes “Comparison Test of Rifle, 5.56-MM, M16A1.”

Singapore receives US approval for an export license to sell M16S to Thailand. This one of the few export sales that Colt and the US State Department will ever approve.

Frankford Arsenal publishes drawings of the 5.56mm SAW case as Sketch BCX-30: 5.56MM Brass Case (Special).

Because of the delay in the design analyses of prospective SAW bullet designs, Frankford Arsenal decides to procure commercial cartridge cases and bullets. These will be handloaded for ballistic tests to confirm additional computer predictions. Frankford orders 1,000 .222 Remington Magnum primed cases, 1,000 .250 Savage primed cases, and various bullets from local commercial sources.

The Justice Department orders a FBI investigation of allegations that Colt has cheated on Government quality-control tests for the M16.

The US Army MTU prepares a lesson outline for the development of a National Match M16A1 rifle. Testing has indicated the superiority of a 1-in-9″ twist heavy barrel over a 1-in-12″ twist barrel of the same profile. Bullet weights as heavy as 70gr are also tested with handloads.

The US Coast Guard publishes the report “Evaluation of the M16 Rifle as a Line-Throwing Gun.” A M16 rifle was adapted to a line throwing gun using an inert Mecar grenade. The results of the test firings indicate that the M16 is an unacceptable line throwing device.

Frankford Arsenal begins experiments with the standard 5.56x45mm case necked up to 6mm. Testing continues through at least May 1972. (Around 1974 or later, Brunswick Corp. submits a similar experimental 6x45mm round as an unsolicited proposal to Frankford. The cartridge is also based on a reformed 5.56x45mm case with a slightly different profile, and is loaded with commercial projectiles.)

The US Army issues a “Materiel Need” document for a “Squad Automatic Weapon, Light Machine Gun.” Before the end of FY 1972, development contracts for ten SAW prototypes are let to Maremont (Saco) and Philco-Ford (later, Ford Aerospace). A design team at the Rodman Laboratory ultimately develops their own candidate, the XM235. The goal is to procure a weapon with an effective range of 800-1,100m that weighs 17-21 pounds when loaded with 200rds of ammo. The ball cartridge must be able to defeat a helmet at 800m, and the tracer must remain visible beyond the same range. Gene Stoner has reportedly advised Cadillac Gage not to bother with adapting the Stoner 63 design to the new requirements.

Frankford Arsenal’s Case Shop is requested to fabricate an additional 800 5.56mm SAW cases with a 0.10″ longer neck. The change in neck length is intended to accommodate a longer bullet design.

Frankford Arsenal receives its order of 1,000 .222 Remington Magnum primed cases, 1,000 .250 Savage primed cases, various commercial bullets, and loading dies. The latter includes forming dies to neck up the .222 Rem Mag cases to 6mm. The 6mm/222 Rem Mag wildcat cases are loaded with the 0.243″ Speer 105gr spitzer and the Remington 100gr “Pointed Special.” The .250 Savage cases are loaded with the 0.257″ Remington 100gr “Pointed Special.” After testing, the .250 Savage is deemed unsuitable, and the 6mm/222 Rem Mag case is deemed to be too small to achieve the desired velocities with 100-105gr bullets.

For unknown motivations, the British ADE decides to rename their 5x44mm cartridge as the 4.85x44mm (based on the diameter of the barrel’s lands).

Andrew J. Grandy files a patent application for a “folded path” cartridge and weapon system.

AMC issues “M16 Rifle: Maintenance Layaway of H&R Equipment.”

Frankford Arsenal publishes the report “Investigation of a Low Noise Duplex Cartridge (LNDC).”

Frankford Arsenal also publishes “Firing Shock Measurements on the M16 Rifle.”

In addition, Frankford Arsenal publishes the report “Compilation of Frankford Arsenal Memo Reports on 5.56mm AR-15/M16 Rifle/Ammunition System (1963-1970).”

Remington issues the report “Tracer Simulation Study.” Under contract to the Army, Remington investigated infrared laser ignition of 5.56mm tracers. The results were mixed as sensitivity to laser stimulation did not correlate to live fire performance.

Mellonics Systems publishes “The Identification of Objective Relationships between Small Arms Fire Characteristics and Effectiveness of Suppressive Fire.” Performed under contract to ARPA, the purpose of this study is to identify objective relationships between small arms weapons characteristics and effectiveness in suppressive fire. In addition, this study provides a methodology through which the suppressive capabilities of various small arms weapons may be assessed. Beside literature searches of battlefield experiences and surveys of combat veterans, life fire testing was conducted using the M1A1 SMG, XM19, M16, AK-47, M60, and M2 BMG. Of interest is that the XM19 ranked far last in perceived dangerousness in incoming fire.

Frankford Arsenal completes fabrication of the 800 modified 5.56mm SAW cases. Again, these are held back in anticipation of test barrels and development of load data. (Once again, it appears that these cases were never loaded as the test barrels were never received, and the 68gr bullet design was never created.)

Frankford Arsenal draws up 6mm variants of the 5.56x45mm case lengthened to 1.898″, 1.981″, and 2.031″. Alternative 6mm cases with a wider 0.410″ case head are also drawn up. These are design studies only, pending a mutually agreeable decision between MUCOM and WECOM‘s R&D agencies.

USASASA holds a PDW conference at Aberdeen.

Rock Island publishes “Investigation of the Interaction of Weapon-Ammunition Subsystems.” Acceptance-test data for five manufacturers’ production of 5.56mm ammunition were analyzed through time-series modeling, an empirical cumulative distribution function was formulated, and a bivariate histogram of chamber pressure and port pressure was developed for use in the selection of weapon-test ammunition.

The BRL publishes “Interior Ballistics Study of the M16A1 Rifle.”

MUCOM, WECOM, and USASASA representatives meet at Frankford Arsenal. It is agreed that the new SAW cartridge will use a 105gr 6mm projectile, possess a 0.410″ case head, have a case taper of 0.1746″ per inch of length, and use a steel case. (A brass cased variant will be designed as a backup.) Frankford Arsenal estimates that the new cases will not be available until August 1972.

Personal Defense Weapons (PDW) Summary Report” is published.

Aberdeen’s BRL releases the report “A Technique for Quality Control of Piston Primer Ammunition.” Sponsored by the USASASA, the study desired to find ways of improving the reliability of AAI’s primer-actuated action.

The BRL publishes “Experimental Ballistic Properties of Selected Projectiles of Possible Interest in Small Arms.” This report includes data collected from test firing 0.224″ projectiles using the “AR2 artillery shape.”

Cornell Aeronautical Laboratory, on contract to Frankford Arsenal, publishes “Determination of Temperature Gradients in 5.56 mm Aluminum Cases.”

ArmaLite ceases AR-18 production at Costa Mesa.

Frankford Arsenal publishes Drawing D-11744216 depicting the new 6mm SAW cartridge case design.

CDCEC issues the four-volume report “XM19 Serial Fléchette Rifle Experiment.”

Stanley Silsby, on behalf of the US Army, receives US Patent #3,672,089 titled “Large Capacity Magazine.”

WECOM publishes the report “Solid Lubricant Coatings Curable at 225 F-300 F.” Experimental solid-film lubricant coatings based on urea-formaldehyde, epoxy-polyamide, epoxy-silane, alkyd-urea, melamine-acrylic, and epoxy-urea resins were formulated for use on the M16A1 rifle. These coatings are cured after being applied to the rifle, and thus low temperatures are needed so as not to adversely affect the rifle’s strength. None of these coatings when cured at temperatures of 225-300F had antiwear or corrosion preventing properties comparable to the fully cured MIL-L-46010A type of solid lubricant coating now used. Of the experimental formulations tested, those based on the urea-formaldehyde and epoxy-silane resins gave the best results. However, with the addition of a curing agent, boron trifluoride monoethylamine complex, to a qualified MIL-L-46010A base, the product could be cured at 275F, and all test requirements could be satisfied.

Frankford Arsenal releases the report “Sealing of Sabot and Primer of XM645 Cartridge.” Waterproof sealing of the sabot and primer of the XM645 Cartridge (SFR) was achieved using a pigmented resin-solvent formulation. Firing tests conducted on experimentally sealed rounds have given every indication that the seals are acceptable. Efforts to effect sealing of the sabot by means of commercially available dry-shrink or heat-shrink preformed plastic caps, or to mold caps having the desired wall thickness, were successful.

Frankford Arsenal completes fabrication of the first 1,500 6mm SAW brass cases ahead of schedule. These used 7.62mm NATO case final draw pieces.

Pier Carlo Beretta receives US Patent #3,675,534 titled “Automatic Rifle.”

Aberdeen publishes the report “Product Improvement Test of Modified Leaf Sight for M203 Grenade Launcher.”

Abraham Flatau files a patent application for the Ring Airfoil Grenade (RAG).

Aberdeen publishes the report “Comparison Test of 5.56-MM Tracer Ammunition Loaded with IMR 8208M and Ball WC844 Propellant.”

Due to bullet seating issues with the 4.85x44mm, the British ADE decide to elongate the case neck, creating the 4.85x49mm. An order is placed with Radway Green for 4.85x49mm cartridge cases.

Edgewood Arsenal issues the report “A Kinetically Non-Hazardous Ring Airfoil Projectile for Delivering Riot Control Agent.”

The US Army Armament Command (ARMCOM) is created. Headquartered at Rock Island, it will combine MUCOM, APSA, WECOM, and USASASA.

The Philippine Board of Investments (BOI) announces that due to the results of weapon evaluations by the Philippine military, only Colt, ArmaLite, HK, and IMI will be eligible for further consideration. The BOI indicates that the co-production program will call for 150,000 rifles to be produced over five years. Domestic content of the rifles will ultimately increase to 100 percent (exclusive of imported raw materials). The foreign firm will provide technical assistance, parts, and materials. The Philippine government will hold the license.

The US ambassador and Lebanese Minister of Foreign Affairs sign a protocol related to a purchase of M16 rifles.

The Philippines opens negotiations to various international arms makers for construction of a domestic small arms plant. Colt and HK are considered to be the front-runners. Colt informs JUSMAG-PHIL that they estimate a cost of $22.5 million to cover the total package of technology, equipment, and materials.

Frankford Arsenal releases the report “Effect of 5.56mm Primer Components on Ballistic Performance of the M16A1 Rifle/Ammunition System” As a result of previous testing at Frankford Arsenal, it was decided to conduct more extensive testing of 5.56 mm primers. A factorial experiment was conducted to determine the effects of these primers on interior ballistics for both ball and tracer ammunition. The primer mixture, the primer weight, and the conditioning temperature of the ammunition were varied to investigate their effects, individually and in conjunction with each other, on the cyclic rate of the M16 rifle, on the action time of the ammunition in the rifle, and on the velocity of the projectile. The results of this test show that within the limits tested, primer components did effect ballistic performance, but to a lesser degree than external factors such as the rifle used and the conditioning temperature of the ammunition.

Frankford Arsenal also publishes the report “Effect of Propellant Additives in Reducing Fouling and Erosion in the M16A1 Rifle.”

WECOM publishes the report “New and Improved Rubber Compounds for Weapon Systems.” The report notes that newly developed fluorosilicone rubber inserts significantly increased the service life of the M16A1 rifle extractor springs.

The new CINCPAC Admiral Noel A.M. Gayler suggests that the Philippine government consider a commercial purchase of M16 from Colt. JUSMAG-PHIL indicates that the Philippine government is currently negotiating for the direct purchase of 7,000 M16.

Frankford Arsenal releases the report “Aluminum Cartridge Case Feasibility Study Using the M16A1 Rifle with the 5.56mm Ball Ammunition as the Test Vehicle.” Identification of the “burn-through” problem associated with high-performance aluminum cartridge-cases was made as the result of studies to isolate the elements of this problem and relate these elements to the interior ballistic cycle of the M16A1 rifle system. One practical solution (the flexible internal element) to this problem was found. This solution was coupled with improvements in mechanical performance of the aluminum case by new analytical design techniques, tougher high-strength aluminum alloy, and novel case processing techniques. With the different improvement combined, the feasibility of the aluminum cartridge case was demonstrated by test firing.

Frankford Arsenal also publishes the report “Investigation of the Piston Primer For Use in the XM645 Cartridge.”

Aberdeen’s BRL releases the report “Resume of Special Tests of the XM19 Rifle and XM645 Ammunition.” These tests were to examine the causes of health related complaints made by troops testing the XM19. Reported aliments included severe nausea, inflammations, and even eye injuries, all apparently caused by particles from the fiberglass sabot of the fléchette cartridges.

The US Army Arctic Test Center begins a new check test of the M203.

The US Army Chemical Systems Laboratory publishes the report “Evaluation of the Wounding Potential of Single Projectiles From the 40-mm Multiple Projectile Cartridges XM576 and the XM576E2.”

Abe Flatau, Donald N. Olson, and Miles C. Miller file a patent application for a pair of non-lethal RAGs, one with a payload and the other without. These become known as the Soft RAG and the Sting RAG, respectively.

GE‘s Richard S. Rose and Burton P. Clark file a patent application for GE‘s version of the Dual Cycle Rifle. It uses an asymmetrical six-chamber cylinder. During its forward stroke, the central operating rod/bolt strips three rounds from the magazine while ejecting three spent cases. During the rearward stroke, three rounds are fired in sequence while three spent cases extracted from the other chambers.

Battelle Memorial Institute publishes the report “Research and Development on Coextrusion of Bimetallic .220 Swift and 25mm Gun Barrels.” This was a research and development program on lined gun barrels directed toward selecting desirable barrel and liner material combinations, which will increase the life of barrels in rapid fire gun systems, and developing the fabrication processes for producing these barrels with a metallurgically bonded liner. Coextrusion was used as the method for producing the lined barrel stock. The program was divided into two parts with the first part directed toward producing lined .220 Swift barrels of selected material combinations for testing in the M60. A-286 steel was selected as the barrel material, and TZM, Mo-0.5Ti, L605, Ta-1 OW, and T-222 were selected as the liner materials for the barrels. All the liners coextruded with the barrel steel satisfactorily over a small mandrel except T-222. The four successfully coextruded combinations were fabricated into .220 Swift barrels with swaging being used to rifle the barrels.

Philco-Ford publishes the report “Development of an Electrochemical Machining Process for Rifling Lined Gun Barrels.” A 16-month program was conducted to advance high performance gun barrel technology by developing an electrochemical machining process for rifling high performance barrel liner materials. A total of 15 electrolytes and numerous electrochemical machining parameters were evaluated in conducting electrochemical machinability studies on iron-nickel-base, nickel-base, and cobalt-base superalloys, and on refractory alloys of columbium, molybdenum, tantalum, and tungsten. Four materials (L-605, VM103, CG-27, and alloy 718) were selected for electrochemical rifling and fabrication into .220 Swift barrel liners. The rifled liners were insulated externally and assembled into outer barrel jackets using a drawing process, thus producing insulated composite test barrels. A total of 12 MG3 test barrels, representing the four liner materials and three jacket materials (H-11, A-286, and Pyromet X-15), were fabricated and delivered to the USAF. The results of this program indicate that electrochemical machining is a feasible process for obtaining high quality and low cost rifling, and that extrapolation of this process to larger calibers appears feasible.

Prior to the manufacture and delivery of Radway Green’s new 4.85x49mm cartridge cases, RSAF Enfield requires preliminary ballistic data with 4.85x49mm pressure barrels. As a result, Enfield is forced to use 4.85x44mm cases with the bullets’ cannelure seated 5mm above the case mouth.

(Next: 5.56mm 1973)

by Daniel E. Watters, Small Arms Historian
Post questions or comments at The 5.56mm Timeline’s Facebook page.

Document History
Publication: 12/10/1998
Last Revised: 05/17/2009


Author’s Note
This article was originally published at The Gun Zone — The Gunperson’s Authoritative Internet Information Resource. My friend and mentor Dean Speir has graciously hosted my articles at TGZ for nearly 16 years. These articles would likely have never appeared online without his constant encouragement and assistance. 

With TGZ’s closure in early 2017, Dean encouraged me to find a new home for my scholarship so it wouldn’t be lost in the dustbin of the Internet. Loose Rounds has welcomed me with open arms. In the future, I intend to expand my legacy TGZ articles and add new contributions here at Loose Rounds.


Comments are closed.