The BAR's rear sight scales were also modified to accommodate the newly standardized M2 ball ammunition with its lighter, flat-base bullet. The M1918A2's walnut butt stock is approximately one inch (2.5 cm) longer than the M1918 BAR's butt stock. The M1918A2's barrel was also fitted with a new flash suppressor and fully adjustable iron sights. Late in the war a barrel-mounted carrying handle was added. Because of budget limitations initial M1918A2 production consisted of conversions of older M1918 BARs (remaining in surplus) along with a limited number of M1922s and M1918A1s. After the outbreak of war, attempts to ramp up new M1918A2 production were stymied by the discovery that the World War I tooling used to produce the M1918 was either worn out or incompatible with modern production machinery. New production was first undertaken at the New England Small Arms Corp. and International Business Machines Corp. (a total of 188,380 new weapons were manufactured). In 1942 a shortage of black walnut for butt stocks and grips led to the development of a black plastic butt stock for the BAR. Composed of a mixture of Bakelite and Resinox, and impregnated with shredded fabric, the stocks were sandblasted to reduce glare. The Firestone Rubber and Latex Products Co. produced the plastic butt stock for the US Army, which was formally adopted on March 21, 1942. The M1922 machine rifle was declared obsolete in 1940, but they were used by Merrill's Marauders in Burma later in the war as a slightly lighter alternative to the M1918A2. Production rates greatly increased in 1943 after IBM introduced a method of casting BAR receivers from a new type of malleable pig iron developed by the Saginaw division of General Motors, called "ArmaSteel". After it successfully passed a series of tests at Springfield Armory, the Chief of Ordnance instructed other BAR receiver manufacturers to change over from steel to ArmaSteel castings for this part. During the Korean War M1918A2 production was resumed, this time contracted to the Royal McBee Typewriter Co., which produced an additional 61,000 M1918A2s. The last US-made variant was produced in 7.62×51mm NATO, as T34 Automatic rifle. In 2006 Ohio Ordnance Works worked on the 21st-century modernization of the BAR, named the "Heavy Counter Assault Rifle" (HCAR).