Originally Posted by RadioActiV
I believe that crowning the barrel keeps the trajectory of the bullet strait. Also resists from dings and dents to the end of the barrel. Causing the trajectory to mess up. That's what I believe, I may be wrong.
+1 Radio, crowning replaces the "true" square cut to the muzzle with respect to the barrel lands.
The primary purpose is to provide the pressurized gas propelling the bullet a path away from the projectile as it exits the bore.
The secondary purpose is to protect the bore from damage caused by misuse.
That, and it looks kool!
Re-crowning is done to repair misuse or prepare the gun for target shooting.
Crowning can be a simple straight cut to finish the barrel's muzzle.
As the bullet exists the muzzle there needs to be equal land influence transferred to the bullet jacket. If the muzzle has been dinged, however slight, its influence is compromised. The level of imbalance has a proportional affect on the accuracy of the bullet. The more the "ding", the more the influence on accuracy.
It can also include a chamfer to recess the crown back from the muzzle. This recess works like bumpers on cars, some light damage to the bumper will not cause the vehicle to function properly.
Typical factory crown:
If the crowning is for target use, here are two types:
Step Type Target Crown
11 Degree Target Crown