06-04-2022, 04:30 PM
danm Wrote:Nice work! Wonder why the 6ARC was adopted by some special units considering this chart???
Technology has changed the assumptions made in these earlier studies. They were based on iron sights and old models of "wounding power". The introduction states: "For the purposes of the study, Hall discounted any effects of gyroscopic instability that induced tumbling or fragmentation." Tumbling (yaw) and fragmentation are now known to extremely important in terminal effects, so this data grossly underestimates the wounding potential from US 5.56x45 ammo at fragmentation ranges, for example. These calculations are highly biased on high velocity generating short flight time, flat trajectory and high kinetic energy. The idea of each soldier having a clear magnified optic and the ability to accurately determine the range was Buck Rodgers science fiction at the time.
The interest into 6ARC has more to do with experience in Afghanistan, improved optics and bullet design. Studies from WWII and Korea indicated that roughly 90% of all fighting occurred at distances less than 300 yards. There are some videos online in which Eugene Stoner stated that infantry did not need a rifle with capability for combat beyond 300m. In the past decade or so however, we began to see reports along the lines of ""U.S. Army data....reveals that more than half of the warÂ’s small arms engagements are now beyond 500 meters" (American Rifleman, Feb 2011). My guess is that the 6mm ARC was developed to meet some spec of a certain amount of energy at some long distance like 800 or 1000m. It may well have a dual spec for DMR use with high-BC lead-core ammo and a lesser one for Steel/brass EPR-style bullets. The EPR will have better behind-barrier effect but a lower BC because brass and steel are less dense than lead. As for why 6mm instead of 6.5mm Grendel, it probably has do do with what was closer to the specification.
In some respects, whereas the 6.8 NGSW was intended to improve upon the performance of 7.62x51 with increased ability to penetrate body armor as well as increased accuracy and effect at long ranges, the 6mm ARC is intended to do the same thing for the 5.56x45.