raindog

November 11, 2009, 04:24 PM

So let's say I have a .308 rifle (caliber chosen at random).

First question: does that mean the measurement is from the top of one land to the other? In other words, if we measured from the bottom of one groove to the bottom of another, it would be wider?

Second question: For a bore of .308", what size bullet would be ideal? .308"? Or would .309" or .310" or .311" be better, so the lands cut into the bullet and grip it as it moves down the barrel? Should the bullet ride "on the lands" or be cut into by the lands?

I have to assume that .307" or smaller would be very undesirable since it would mean the bullet was "skipping down the bore" and bouncing up and down off the lands...but I am speculating.

For my .308, I am loading Sierra #2200 bullets, which are "30 cal .308 diameter". So let's assume the barrel is brand new...the rifling will lightly contact the bullet - so the rifling really is just there to impart spin, right?

Now let's say it's 20,000 rounds later through the same barrel. Presumably the lands are worn down a bit. What is the effect? Well, reduced accuracy, I know that ;-) But I assume that means that the barrel is (a) not making good contact with the lands, (b) not spinning properly, and (c) perhaps having some reduced velocity as the "seal" is not good and the bullet isn't pushed as hard (?)

First question: does that mean the measurement is from the top of one land to the other? In other words, if we measured from the bottom of one groove to the bottom of another, it would be wider?

Second question: For a bore of .308", what size bullet would be ideal? .308"? Or would .309" or .310" or .311" be better, so the lands cut into the bullet and grip it as it moves down the barrel? Should the bullet ride "on the lands" or be cut into by the lands?

I have to assume that .307" or smaller would be very undesirable since it would mean the bullet was "skipping down the bore" and bouncing up and down off the lands...but I am speculating.

For my .308, I am loading Sierra #2200 bullets, which are "30 cal .308 diameter". So let's assume the barrel is brand new...the rifling will lightly contact the bullet - so the rifling really is just there to impart spin, right?

Now let's say it's 20,000 rounds later through the same barrel. Presumably the lands are worn down a bit. What is the effect? Well, reduced accuracy, I know that ;-) But I assume that means that the barrel is (a) not making good contact with the lands, (b) not spinning properly, and (c) perhaps having some reduced velocity as the "seal" is not good and the bullet isn't pushed as hard (?)