Accuracy and Jump Measurements of the 5.56-mm M855 Cartridge

Report No. ARL-TR-5540
Authors: Ilmars Celmins
Date/Pages: May 2011; 48 pages
Abstract: The U.S. Army Research Laboratory (ARL) performed a jump test and analysis to evaluate the accuracy of the M855 projectile when fired from the M4 weapon system, and from a Mann barrel for comparison. The firings consisted of a four 10-round groups, each in a different configuration, fired through the ARL Aerodynamics Experimental Facility spark range. The performance from two different standard barrels was similar. Removal of the compensator resulted in slightly increased muzzle motion, which can be attributed to removal of mass from the muzzle. The Mann barrel exhibited drastically reduced muzzle motion. The largest jump component dispersion contributors for all four configurations were the relative center of gravity (CG) jump and the aerodynamic jump. Strong interactions were identified between relative CG jump and aerodynamic jump, which served to reduce the total jump. The overall effect of the compensator was positive, in that it resulted in lower total jump dispersion due to strengthened negative correlations. For the Mann barrel, there was a decrease in magnitude and dispersion of all jump components, most likely due to the fact that lower gun motion imparted smaller linear and angular impulses to the bullet. One implication is that the Mann barrel provides a significantly different dynamic launch environment than the standard M4 weapon, which must be taken into consideration when using Mann barrels to evaluate ammunition performance other than aerodynamics.
Distribution: Approved for public release
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Last Update / Reviewed: May 1, 2011