“The cartridge case was developed really from the ground up,” he said. “Every part of the cartridge was evaluated. Initial testing showed that the brass cartridge case – really existing 7.62 cartridge designs – did not give us the accuracy that we needed. We developed a new 7.62 match mil-spec cartridge case from our .308 Gold Medal Match line. What that gave us was the .308 ‘tighter tolerances.’ We [also went] to 7.62 head hardness and the neck hardness required for semi-automatic weapons.”
Primer assemblies were the next subsystem to be evaluated. After testing eight different options, the Federal Gold Medal GM210 primer was selected as the optimum solution.
“The projectile was evaluated next,” Leis continued. “15 different projectile designs were tested. The projectiles varied widely – we tested projectiles from 158 grains all the way up to 200 grains – and the Sierra® Match King® .30 caliber 175 grain projectile was selected for this cartridge. Propellant was then evaluated, especially for the extreme temperature stability performance. Twenty different existing propellants and different blends were evaluated. A modified custom extruded propellant was chosen for this cartridge. This propellant is stable across temperatures and exhibits much reduced flash characteristics.”
“From that a manufacturing process was designed. The cartridge can be assembled on conventional high speed loading equipment – it is the same equipment that is used to produce Federal’s Gold Medal Match ammunition. Along with this manufacturing process we set up some unique quality controls. Also a unique test plan was established for the manufacture of this cartridge and meeting the performance requirements,” he said.
NSWC – Crane’s Stoll then returned to the podium, noting, “We selected the 175 grain Sierra® MatchKing® and ended up with a propellant that, from our testing, indicated that it was stable across the operational temperatures we had established. And we had reduced flash signature as well.”
In terms of initial results, he said, “So far we have had some raw results come back from the five lots that Federal has produced…and we have gotten 1.6 inch – 1.8 inch results at 300 yards. So it’s been fairly consistent so far.”
In addition to the development of the new Mk316 Mod 0 for 7.62mm sniper rifles, NSWC – Crane representatives have also been working on an upgrade to the current .300 Winchester Magnum Mk 248 Mod 0.
Noting that the current 190 grain .300 Win Mag cartridge has a published effective range of 1,200 yards, Chuck Marsh, NSWC – Crane, observed that recent testing revealed a user desire “to increase that effective range from 1,200 yards to 1,500 yards. We also wanted to decrease wind drift and have flash reduced.”
The resulting Mk248 Mod 1 contract award is projected for the middle of June 2009.