Little confused here as well, and I have not been up in Seward's Folly.
C3 is correct as usual. The diameter of the bullet is a tad larger than the diameter of the rifling on a barrel. That way, the rifiling can grip the softer bullet and spin the bullet to stablize it during flight. The groove diameter is nearly equal to the bullet diameter so gasses won't just blow by the bullet.
Skullcrusher, you are evil, sick, demented, twisted- and my hero!
Originally Posted by pandamonium
...without the Second, we cannot protect the rest!