Push the tip/end of your thumb into the emery or paper, which will push the abrasive into the muzzle. The softness
of your thumb will make the crown polishing, smoothly rounded, rather than sharp edged as done with a lathe cutter.
Then rotate your wrist, turning it to the right, back to the left, right, left, right, left - turn the barrel 90 degrees
and continue rotating your wrist which is twisting the emery or paper in the muzzle.
When the rifle was made, there was a machined cut made at the muzzle of the barrel - like a short 45 degree angle.
The muzzle is not square, that is, it is not flat right across the top with the rifling right at the to surface. The machining
of the muzzle with a cutter has left a sharp edge or corner at the bottom of the grooves and at the tops of the
lands.
Using the emery or paper will smoothly round these corners, which will make loading tighter combinations easier
and without cutting the patch.
The proper angle for moving metal, which is called "drawing", is a short smoothly radiused corner, not a long tapered
cone. When you load a tight ball and patch combination into the muzzle, you are actually drawing the metal (ball) into
a slightly elongated projectile, which is encased in the cloth patch. This must be done without damaging the patch.
Sharp crowns will cut a tight combination's patch, which promotes burn-through and poor accuracy.
This is a crown polished as I noted, using the emery and/or wet/dry abrasive 320 paper.
You can click on the next two pictures to get an enlarged view.
That said, DaveC has made a tool that actually cuts the crown with smoothly rounded edges, however he does not sell
this marvelous creation.
This is the crown cut by Dave's tool.
This is the crown (rather deep one at that) of a non-polished muzzle, simply cut on a lathe with a 45 degree cutter.
There is a sharp corner at the top of each land, and at the bottom of each groove. Those are the 2 areas that need smoothing.
