http://www.angelfire.com/art/enchanter/bullet.html. Page from Phil West's Scrapbook.
Click on the link for some interesting dicussion on potential replacements for the 5.56mm cartridge, including the Remington 6.8mm SPC and the 6.86x35mm ARC (aka the.270 ARC), the author's preference.
Don't bother unless you're really interested in this stuff.
We've read the Remington 6.8mm SPC is based on the .30 Remington case, but J.D. Jones makes this observation:
"I fooled around with the 25, 30 Rem case a long time ago. It is simply a 30-30 case turned into rimless. Case head expansion was a problem before ballistics got interesting. I would expect the 6.8mm SPC case head has been considerably strengthened over commercial brass. I do not believe those ballistics will come from modified commercial brass safely."
Click on "return to Scrapbook" at the bottom of the page to find an index of other pages of possible interest.