Brownells sells a hand turned piloted crowning tool, with different interchangeable bore sized pilots. Unfortunately the chrome lining in the NORC barrel is harder than most tools, so your EXPENSIVE cutter won't last long.
If you really want to DIY, you look for a carbide router bit with a 1/4" shank, and a 1/2" shoulder sticking out near the bottom [ for crown molding ]. Some carbon fiber arrow shafts have a 1/4" ID. and a .298" OD. Slip a 3" section of well lubricated arrow shaft over the 1/4" router bit shank, and you have a .298" pilot/guide, which fits almost perfectly into the bore. Then turn the carbide router by hand [ carefully - these are SHARP ] until the 1/2" carbide shoulder cuts a nice neat new square crown deep enough to actually improve things.
Take a new q tip and run it into the bore, over the edges of the new crown ... if the q tips don't leave any bits behind, then the edge is clean and ridge free enough that the bullet will come out nicely.
OR ELSE,
pay the man ...
GOOD LUCK
LAZ`1