Quoted:
I have done some beautiful touch ups with the old brass Screw and grinding compound.

Round head slotted screw, sized between the muzzle and the bore, some Clover or the like valve grinding compound. ( ebay or local auto parts store.)

Light nick or just roughness, use a milder abrasive 320 or so, if its a bigger nick, you might consider a more aggressive compound, 180 or 220.

Put a patched jag in from the other end, ready to push out the muzzle, just a half inch or so down the bore.

Glop the compound on the screw, and gently, at slow speed with a dremal or drill , grind, while moving the tool to constantly change the angle, rotating it around.

If you are already boogered, and considering renting or buying an expensive recrowning tool, or paying a gunsmith, you've got nothing to loose trying this.

I have used it on my Ruger Number One in 270, my 10/22, and a $99 M4 barrel that looked like the chrome was hanging out of the bore.

All three rifles shoot beautifully, the screw made a really nice, concentric bevel cut.