During early load development for ArmaLite in 1957, Robert Hutton used IMR 4198, IMR 3031, and an unnamed Olin Ball propellant. At this point, the main goal was to show that the 55-grain bullet @ approximately 3,300 feet per second could indeed penetrate a helmet at 500 yards. However, all of this testing was performed with a 22-inch barrel. When Remington delivered the first lots of .222 Special (later renamed the .223 Remington), the cartridges were loaded with IMR 4475. Introduced in 1936, IMR 4475 was then in use by Remington for production of military 7.62mm NATO cartridges. Use of IMR 4475 with the smaller cartridge continued on through to the early '60s with early military production lots.

When the military-wide adoption of the M16/XM16E1 was forced in early 1963, Frankford Arsenal was assigned oversight of the procurement of .223 Remington ammunition. An early advocate of Small Caliber/High Velocity (SCHV) military cartridges, William C. Davis, was assigned as Frankford's "AR-15 Project Director." The original military technical data package (TDP) for the ammunition was based upon Remington's own factory specifications and TDP. However, Frankford Arsenal quickly found that IMR 4475 could not reliably achieve the quoted 3,250 fps from a M16 without exceeding maximum chamber pressures. It was one thing when Remington was turning out small quantities of .223 Remington and could cherry-pick suitable production lots of IMR 4475, and quite another when it was faced with mass production of the cartridge. The choices were either to lower the velocity, increase the acceptable pressure specs, or change propellants.

The representatives from the Office of the Secretary of Defense (OSD) to the Technical Coordinating Committee (TCC) vetoed lowering the velocity specs, reportedly on behest of the US Air Force (USAF). However, it was warned that increasing the chamber pressure specs would be technically unwise given trials in which the cartridges were already prone to popping primers. When the earliest bid solicitations for M193 Ball were released later in 1963, the OSD-sponsored specs demanded 3,250 fps with a Remington-style 55-grain FMJ (instead of the original Stoner/Sierra design), IMR 4475, and no change in pressure specs. In return, Remington, Olin/Winchester, and Federal Cartridge all refused to bid. Olin objected to certain specifications on cartridge case wall thickness and to the specification of IMR 4475 propellant. Remington objected to the same case specifications and recommended that the prescribed maximum mean chamber pressure be increased from 52,000psi to 53,000psi. Federal Cartridge expressed the view that the maximum mean chamber pressure should be raised to 54,000psi.

At the same time, the USAF was still independently ordering its own 5.56x45mm ammunition from Remington. Late in 1963, Remington asked permission to switch from IMR 4475 to Olin's WC846. The latter was in use by Olin for military production of 7.62mm NATO ammunition, just as Remington had done with IMR 4475. With TCC approval, the USAF accepted Remington's recommendation in December 1963. However, for the time being, the Army intended to stay with IMR 4475 for their own 5.56x45mm ammunition.

In January 1964, a meeting was held at Frankford Arsenal with representatives of Remington, Olin, Federal Cartridge, DuPont, USAF, and Army to review the requirements of the ammunition TDP. DuPont complained that it must manufacture lots of IMR 4475 that will develop a maximum mean chamber pressure 2,000psi less than that permitted to cartridge manufacturers. DuPont also expressed concern as to whether or not the company could consistently meet a chamber pressure limit increased by only 1,000psi. However, there would be no problem in supplying enough propellant to load one million rounds. The Army agreed to change the cartridge case drawing to reflect the new dimensions proposed by Remington, because Remington maintained that its first drawings had been misinterpreted by the Army. In addition, the Army agreed to a temporary waiver for the M193 pressure specs for only the first order of one million rounds. The average chamber pressure limit for the powder was increased to 51,000psi, and the limit for cartridges was increased to 53,000psi, with individual rounds allowed to test as high as 60,000psi. In response, Remington and Olin agreed to supply 500,000 cartridges each under this waiver.

However, the Army was now faced with the issue of how they were going procure their remaining FY1964 ammunition requirement of 149 million additional rounds. In March 1964, Remington and DuPont complicated matters by withdrawing IMR 4475 for use in future production lots of M193. Fortunately, Frankford Arsenal had already been granted permission to test production lots of 25,000 rounds loaded with alternate powders. Candidates included DuPont's CR 8136 (another IMR type), Hercules' HPC-10, and Olin's WC846. HPC-10 was rejected due to low temperature pressure issues along with its propensity for bore erosion. WC846 had been an early favorite in part due to USAF acceptance of ammo lots loaded with the Ball propellant. However, rifle acceptance testing by Colt with the early lots of WC846-loaded ammunition showed an increase in cyclic rates. The higher cyclic rates were ignored by the USAF, who simply increased the M16's maximum acceptable cyclic rate to match. The Army was more concerned, but issued month-by-month cyclic rate waivers for their XM16E1 instead. Other than the higher cyclic rate, no one perceived any future issues at the time. Colt's senior product engineer Foster Sturtevant even wrote in an internal report weeks later that the higher gas port pressures with WC846 were "in no way harmful to the AR-15" and would lead to more positive functioning of the rifle.

In April 1964, the Army approved two powders for use in loading M193: CR 8136 and WC846. Predictably, Remington chose to use its parent company's CR 8136, while the other manufacturers selected WC846. Although it also displayed higher pressure levels at the gas port, CR 8136 did not have as dramatic effect upon the cyclic rate as did WC846. As soon as Remington had production lots of M193 with CR 8136 available, the Army withdrew the month-to-month cyclic rate waivers for the XM16E1. Unfortunately, like IMR 4475 before it, the performance of CR 8136 was not stable from lot-to-lot, and Remington had a difficult time maintaining the maximum chamber pressure specs. By December 1964, Remington and DuPont withdrew CR 8136 for the production of M193. In order to finish the remainder of their production contract, Remington sought permission to resume use of WC846, and this change was duly approved. However, XM16E1 acceptance testing at Colt continued with the remaining stocks of CR 8136-loaded M193 cartridges.

Colt's supply of CR 8136-loaded ammo did not run out until the early summer of 1965. When the Army refused to grant additional cyclic rate waivers with the use of WC846-loaded ammo, Colt in turn suspended production of the XM16E1 in favor of the USAF's M16. This led to yet another search by Frankford Arsenal for an alternative powder. While Olin declined to participate, two other propellants were submitted: DuPont's EX 8208-4 (yet another IMR type) and Hercules' HPC-11. DuPont's EX 8208-4 displayed moderate fouling, but it also recorded higher gas port pressures than even WC846. Hercules' HPC-11 showed the least visible fouling, but closer examination unveiled that heavy fouling was constricting the gas tube. Frankford Arsenal's final report recommended that EX 8208-4 be approved for use in M193 Ball and M196 Tracer cartridges, and that Hercules and Olin reduce the fouling characteristics of their respective powders. Unlike WC846, HPC-11 was not approved for use. However, M193 and M196 cartridges loaded with DuPont EX 8208-4 would not enter the supply chain until June of 1966.

Between March 1965 and September 1966, 99 million rounds of 5.56x45mm were delivered to US troops in South Vietnam. Of this amount, only 10 million rounds were loaded with CR 8136; the rest had WC846.

In December 1967, WC846 was withdrawn for use in loading M196 tracer cartridges. WC846 was replaced by DuPont's IMR 8208M (formerly EX 8208-4). Ironically, production lots of M193 Ball loaded with IMR 8208M were soon withdrawn for practice use only. Reliability problems had been discovered in a new set of performance trials conducted by the USMC at Fort Sherman7 in Panama. Part of the goals was to sort out the relative merits of Ball versus IMR powders in the reliability of the M16A1.

The fouling issue with WC846 did not come to a head until a rifle ceased to function in endurance testing due to a clogged gas tube. This particular lot of ammunition was found to have an unusually high percentage of calcium carbonate, an ingredient in Ball powder used to neutralize excess acids. Two years of testing by Frankford Arsenal noted that few lots of WC846 ever came close to the allowable maximum of one percent of calcium carbonate. (This was the same amount specifically mentioned in the original patent from thirty years earlier.) However, in September 1969, Olin hedged their bets and reduced the allowable maximum of calcium carbonate to 0.25 percent. In January 1970, Olin took a further step and divided the tolerances of WC846. They finally discovered/admitted that lots of WC846 suitable for 5.56x45mm were at the opposite end of the tolerance range from lots suitable for 7.62mm NATO. Henceforth, the 5.56x45mm suitable tolerance range was relabeled as WC844. The 7.62mm NATO-suitable tolerance range remained known as WC846. WC844 is still used for loading 5.56x45mm ammunition.

Quoted:
This is from Daniel Watters' site, an excellent resource any AR15 fan should set aside some time to study:



The Great Propellant Controversy