Dating m1 garand stocks
Its overall length is the same as 5.56mm, at 2.26″/57.4mm, though some magazines are advertised as offering overall lengths as long as 2.315″/58.8mm, and the purpose-built Six8 rifle from LWRC, which uses proprietary magazines, offers an overall length of 2.32″/58.9mm.
The cartridge has a case capacity of between 34.8 and 36.9 grs H2O (2.255-2.391 ccs), 14-21% more than the 5.56x45mm.
This was the original programmatic evolution proposed for the SOPMOD Mk12 Special Purpose Rifle (SPR) system, the interim result of which was the fielding of the Mk262 77-grain ammunition, with a planned later transition to the Enhanced Rifle Cartridge (ERC) capability in a mid-bore 6.5mm, 6.8mm or 7mm caliber.
With the already proven combat success of the Mk12 SPR, the SPR concept-development team went to manufacturers in the US ammunition industry for assistance.
It uses standard .277″ diameter projectiles, although it is limited in its selection of those by the overall length.
In general, though the projectile diameter is the same, the 6.8mm Remington requires totally new projectiles versus existing .270 caliber rounds.
In terms of cartridge design within a given OAL, longer ogives come at the price of less case capacity and therefore lower muzzle velocity, but in general accepting this comes with the benefit of better velocity retention over distances beyond about a hundred meters.
In light of this, the 6.8mm SPC’s maximum ogive length is the first curiosity of the cartridge’s design.
Increasing the ogive length either increases the cartridge overall length or necessitates a decrease in case length (reducing its capacity, unless the case head diameter is increased).
That’s one reason why it’s extremely puzzling to me that one of the most popular 5.56mm replacements – and the round many think offers the military a commercial-off-the-shelf improvement in effectiveness – offers even less in these criteria than even M855.
That round is the 6.8mm Remington Special Purpose Cartridge.
The Special Forces SPC team require that the powder used is to be manufactured in the United States, and contain an organic flash inhibitor to decrease muzzle flash in low light conditions.
Remington began the final development of the SPC cartridge in the fall of 2001, using concept wildcat brass made up by MSG Holland from shortened .30 Remington cartridge cases.
Auto CAD drawings of the prototype calibers in the same cartridge case were prepared by Cris Murray of the US Army Marksmanship Unit.