The 'trick' is to bring the flutes up to contact on the land(s) and with just a bit of downpressure rotate the cutter (by hand!) to just shave the land(s). As it gets them all down evenly, then only give it that tad of rotation more to chamfer the bottom of the grooves, make yourself stop, and use that acorn nut idea to finish the job. It is easy to try to do this too fast; take your time.
If you could have a muzzle perfectly flat with no crown at all, and no burrs, it would shoot fine. Things being what they are, that chamfer 'ring' around the muzzle must also be straight. square, and even to release the gas pressure evenly from behind the bullet as it exits the muzzle.