I believe I almost have this figured out.  Headspacing is the issue.  When a new bolt is used on an existing barrel, and the finding is the headspacing is out of tolerance, you need a new bolt.  You cannot change the headspacing by adjusting the barrel extension or existing barrel length.  If that is true, why would anyone purchase a new bolt and take his chances that it will fit?  The reason I ask this question is because I have heard, "try bolts until you find one that fits."  Thanks

bybon, you understand the situation correctly. If all the involved parts (barrel chamber, barrel extension and bolt) are manufactured and assembled to be within correct industry standard tolerances, the bolt should headspace correctly. That means everybody had to do their job correctly. The new bolt/barrel assembly should be checked with the correct headspace gauge, to be safe. A gunsmith can check headspace to determine proper fit before firing the rifle, usually, for a small fee. Like I said, it should fit, but why take the chance?

coyote3

Thanks coyote3.  That is all I wanted to know.