Crane,
As I understand things when a barrel is lapped it gets "belled out" on both ends when the lead swage comes in and out of the barrel. Thats not really a big deal on the chamber end becuase it gets opened up past that point when its chambered, on the crown end it's bad juju. So they usually cut at least 1" off that end.
Plus you lose a little when the ends are squared up for chambering or crowning, but that amount is usually minimal.
Chris