From: bartb@hpfcla.fc.hp.com (Bart Bobbitt)
Subject: Re: Throat Erosion??
Organization: Hewlett-Packard Fort Collins Site

william E Davidsen (davidsen@yeti.crd.ge.com) wrote:

:   I have a friend who shoots 1000yd matches, and I'm pretty sure he
: quoted his barrel life as 200 rds. He's given me a few nice top name
: barrels, but they are no longer accurate and need to be bored to a
: larger caliber to restore accuracy.

Reboring barrels to a larger caliber has often been done.  For hunting
barrels, a reasonable degree of success occurs.

But for target or match grade barrels, the accuracy typically won't be
as good as with the original smaller caliber.  The reason is the rifling
process causes the first inch or so at each end to be non-uniform in
dimensions.  When a bored blank is rifled, the support of the rifling
tool is not too good at the ends of the blank.  This causes a slight
dimensional variance of a few ten-thousandths of an inch.  Some barrel
makers cut these ends off of the muzzle end and may or may not cut them
off the chamber end.  At the chamber end, these variances don't matter
as they are usually removed by the chamber reamer.  Other barrel makers
will mark the rifled blank at each end somehow and indicate that the
dimensional uniformity is only between these marks.  This tells the
person who installs the barrel in a receiver where he needs to limit
the finished barrel length to for best accuracy.

BB