5.56 X 52 XPL (SPECIAL CASE 2.049″)



The following is an excerpt from the ICC newsletter #289-290 (Jan-Feb 1980)


“During July 1971 a computerized parametric design analysis (PDA) was started at Frankford Arsenal to determine the ammunition concepts to meet the SAW user requirements. Five candidate designs–5.56MM, 6.00MM, 6.35MM, 6.5MM (all using conventional steel or lead core jacketed bullets) and a 6.5MM steel flechette concept were initially studied. The refinement of these efforts during August 1971 resulted in the concentration on two calibers: 5.56MM (.224) and 6.00MM (.243) using either a lead or steel core jacketed bullet. (This was the first use of a math model for small arms cartridge design–the printout of which gave data on basic design parameters such as bullet weight, bullet length, barrel length, muzzle velocity, chamber pressure, basic case dimensions, systems momentum, weapon weight, etc.)

The 5.56MM (.224) cartridge was based on a lead core 68 gr. bullet with a case having an enlarged body and longer length (length 1.949 inches, head diameter .4313 inches and shoulder diameter .4055 inches) as compared to the standard 5,56MM, The actual design effort took place during November-December 1971 and resulted in a brass case very close to the original parameters set forth in the caliber .224 PDA math model computer printout (30 August 1971); however~ minor dimensional changes were made in head to shoulder length and the case body taper to better utilize the Arsenal fabrication process and to utilize existing case components (17~62MM final draw pieces trimmed to 1 3/8 inches). The resulting design was recorded on Frankford Arsenal Sketch BCX-30 dated 10 January 1972, entitled: 5.56MM Brass Case (Special). Some very limited fabrication (about 100 pieces) of this case took place at Frankford Arsenal (Building 215) during the period December 1971 to January 1972 with 1.949 inches case length, headstamped FA 71 (FIG. i). These cases were held awaiting the availability of a lead core 68 gr. bullet and procurement of a special test barrel. During March 1972 the case shop was requested to fabricate an additional 800 5.56MM Special Cases to Sketch BCX-30 but with a 0,10 inch longer neck (2.049 in. case length) for a lengthened bullet design. These were completed 30 April 1972 (headstamped FA 71) and held in Building 215-B awaiting loading data and subsequent ballistic test to verify the prediction of the PDA math model.

There is absolutely no evidence to indicate these 5.56MM Special cases were ever loaded, since the test barrels chambered for both case lengths (1.949 in. and 2.049 in.) were never received and no loading data could be located. In addition, the design effort was never completed on either a 68 gr. lead core bullet or a lengthened bullet for these cases. It should be pointed out that as late as July 1972 Frankford Arsenal records mentioned that the 5.56MM Special cases were still awaiting ballistic testing because the necessary test barrels and fixtures had not been received.”