An unfired .25 Auto bullet is about .251. It will be pushed thru a barrel slightly smaller in diameter than that. Each groove is ABOUT 1-2 thousandths of an inch deep. So a barrel with an even number of lands and grooves would have a barrel where bottom of groove to bottom of groove (your red line above) would be 2-4 thousandths greater than top of land to top of land (blue line above).
The number, shape, depth and width of the groove in rifling will vary from caliber to caliber. For instance, not all grooves are square- some look like a triangle.
What we have here is... failure- to communicate.
Last edited by c3shooter; 11-21-2013 at 04:21 PM.