I firelapped my son's 338-378 this spring. i started with 5 rounds of the medium then 5 with the fine. Then 10 strokes cleaning with the lasso or jb bore paste. Not sure if it helped much on accuracy but certainly didnt hurt and cleans easier now. After bedding and firelapping it shoots consistent 4" groups at 500 and ragged hole at 100. I would Not do it on a chrome barrel or a custom barrel.