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Twycross · February 15, 2006, 03:43 AM

Disclaimer: This is how I understand it to be. Anyone who sees me in error, please correct me.

The bullet diameter is typically equal to the distance between the grooves, or valleys, leaving it slightly larger than the diameter as measured by the lands. This is why you cannot stick a bullet down the muzzle (at least, you shouldn't be able to). So in the 9mm example, the bullet diameter is .355 inches. For argument's sake, we'll say the lands are each 0.001 inches high as measured from the grooves. So the bore diameter as measured from the grooves is .355 inches, equal to the bullet diameter, while the bore diameter as measured by the lands is .353 inches.

When the bullet is fired, the pressure forces the bullet down the barrel, and the lands dig into the bullet, slightly deforming it, and that grip is what forces the bullet to initiate it's spin. If you've ever seen, or get to see, a fired bullet, you should be able to see the indentations from the lands.

Hope this helps.

February 15, 2006, 03:43 AM	#2
Twycross Senior Member Join Date: January 26, 2005 Location: Montana Posts: 1,187	Disclaimer: This is how I understand it to be. Anyone who sees me in error, please correct me. The bullet diameter is typically equal to the distance between the grooves, or valleys, leaving it slightly larger than the diameter as measured by the lands. This is why you cannot stick a bullet down the muzzle (at least, you shouldn't be able to). So in the 9mm example, the bullet diameter is .355 inches. For argument's sake, we'll say the lands are each 0.001 inches high as measured from the grooves. So the bore diameter as measured from the grooves is .355 inches, equal to the bullet diameter, while the bore diameter as measured by the lands is .353 inches. When the bullet is fired, the pressure forces the bullet down the barrel, and the lands dig into the bullet, slightly deforming it, and that grip is what forces the bullet to initiate it's spin. If you've ever seen, or get to see, a fired bullet, you should be able to see the indentations from the lands. Hope this helps. __________________ The test of character is not 'hanging in' when you expect light at the end of the tunnel, but performance of duty, and persistence of example when you know no light is coming. - Vice Admiral James Stockdale, USN (ret.)