General info…
The goal of using J-B is to smooth down the microscopic surface fretting that remains from the manufacturing processes of reaming and rifling. You can think of it as millions of tiny burrs that cover the landscape of the bore. As the pellet slides through, soft lead abrades from its surface and sticks and builds up over time which causes accuracy to degrade.
If the bore is especially rough, a polishing regimen may produce a slight velocity increase but the main advantage is to extend cleaning intervals. It also makes the cleaning go easier when the time comes.
I agree with Edward (elh), that the most effective way to do it is with a rod and snug-fitting patches to get a good scrubbing action. I expect pull-throughs would take hours of effort to do what would take 5 minutes with a rod. Fire-lapping is an alternative but also relatively slow and tedious.
I use a ball-bearing rod so the scrubbing action follows the rifling. Some guys don’t concern themselves with this aspect and seem to get satisfactory results but it seems to me it misses the tiny inside corners of the rifling where lead already wants to stick. Working from the breech end, I typically apply 100 strokes distributed as follows…25 strokes to 25% of its length, another 25 strokes to 50% of its length, another 25 strokes to 75% of its length, and a final 25 strokes to the full length. I don’t measure the distance, approximate is good enough. The intent is simply to apply progressively fewer strokes at the muzzle…the breech gets about 100 strokes and the muzzle gets 25 strokes.
Use a new patch (or VFG pellet if you’re using the Brownell’s stuff) every 25 strokes or so, or when it is has worn to the point where it’s not applying decent pressure against the walls of the bore. With each new patch, you will notice some reduction of friction as the surface fretting becomes smoothed down.
Side bar about the Brownell VFG system, a nice feature is the felt pellet can be threaded down onto the tapered rod adapter once in a while and that acts as a wedge to force it back into firm contact with the bore. There’s no VFG for .177 cal though so for that I just use a brass jag and cotton patches.
Don’t let the patch exit the muzzle or the crown will develop a subtle bell mouth, and you’ll have to re-dress it. I clamp a stop block at the muzzle so I don’t have to monitor it.
If you want to then carry it a step further, clean the bore and follow up with a similar treatment using a finer compound like J-B Bore Bright, Flitz, etc.
Lastly, it pays to spend a little more time at the breech end to smooth the leade...specifically the leading edge of the rifling. Many barrels have a sharp step where the rifling begins, left behind by the blunt end of the reamer that was used to cut the leade. If that is left untreated, the pellet will tend to snag as it is being chambered, cutting it and causing it to chamber crooked. When I see that, I start with a something more aggressive like 400 and 600 grit wet/dry on a dowel to break the sharp edge. Or you can use a Cratex point (rubberized abrasive bit) if you’re careful. Then the polishing treatment further smooths the step so pellets will ease into the rifling, staying neatly centered and undamaged.
I hope I didn’t leave anything out
