http://www.pac-nor.com/care/
CHECK OUT THIS LINK IT GIVES AS GOOD an explination as i have read

DO NOT HANDLAP A BARREL UNLESS YOU ARE IN THE PROCESS OF FABRICATING IT.

YOU WILL WEAR OUT THE THROAT AND 1" OR MORE DEEP FROM THE MUZZLE.

hiredgun-

It is my understanding that any lapping done (with a lead lap on a rod) should be done BEFORE the barrel is chambered and cut to length and crowned. The reason is that when the lap is reversed on each stroke it tends to enlarge the bore. This enlargement is removed by the chambering and cutting to length. Hand lapping should NOT be done to a barrel that is ready to shoot.

My $0.02.

Bob

Some folks have stated that handlapping a new barrel will aid accuracy and lessen future copper fouling. But how do I do it and should I? Thanks.