I believe Crowning the barrel is intended to protect the exit edge of the tube from possible damage thru accidental impact with other objects. Various angles or shapes are employed to place the barrel exit edges behind protruding metal making it very difficult to ding the exit edge.

For the past 20 years, my policy as been to recrown everything that either i or my customers own---rifles, revolvers, & auto pistols. THE CROWN MUST BE CUT EXACTLY 90 DEGREES TO THE CENTERLINE OF THE BORE. A PRECISION CROWN WILL ALLOW THE GAS PRESSURE AROUND THE BASE OF THE EXITING BULLET TO BE AN EVEN 360 DEGREES AROUND. ANY DEFECTS AT THE CROWN WILL CAUSE UNEVEN PRESSURES EXERTED ON THE BASE OF THE BULLET AS THE BULLET EXITS THE BORE, THUS THE BULLET WILL BE PITCHING & YAWING AS IT ATTEMPTS TO STABILIZE ITSELF.

I use the 45 degree crowning tool sold by brownells for all the work. The crown is re-cut, lapped with several abrasive compounds, & then hand polished with 3 grits of 3m metal finishing pads. I then polish the new crown with a dremel tool, felt bob tip, & flitz or maas metal polish.

Typical charge for this work is $40.00----it really make a heck of a difference in the accuracy potential of your firearm. PS: PLEASE DISREGARD THE CAPS. I HAVE HAD SEVERAL MINI-STROKES WHICH HAVE AFFECTED THE QUALITY OF MY VISION. I AM RETIRED AND CAN NO LONGER HOLD DOWN A CONVENTIONAL JOB AS I DID FOR THE PAST 32 YEARS.

Hey, Guru...
I'm sorry to read that you've has a few strokes. That can't've been fun! I hope that you have a successful, complete recovery.

Instead of typing ALL CAPS, how 'bout switching to a larger-size type instead? For instance, so far this post has been in size 3.

This is in size 4.
And this is size 5.

(Back to size 3 again.) The sizes-choice box is up at the top of the compose-a-message box, a bit to the left, next to "fonts."

Give it a try.