Fire lapping is usually used to attempt to "repair" a pitted bore or such. There is no reason to fire lap a new bbl at all. I would recommend using JB's and Kroil to clean and lap the rifling before you ever fire it to make sure any burrs are worked out and don't get permanatly imbedded into the bore.
The only person I've ever known who has actually fire-lapped a bbl was my local gun dealer, who accidenly left some ammonia based cleaner in his bore and forgot about it. It pitted the bbl on his Colt National Match quite badly. He did the JB's treatment and then bought some fire lapping bullets and actually got the gun to shoot 5/8's groups again. It was a 1/2" gun before though, so there is a reason to fire lap, just no really a reason to fire lap a new bbl. Escpecially rounds that have short bbl lifes to begin with.
