The very end of the muzzle of a rimfire or centerfire rifle that is recessed in order to protect the riflings in the barrel. As the bullet exits the muzzle, any damage to the end of the riflings could affect adversely the trajectory of the bullet.
The muzzle edge of the barrel -- called the crown -- will be finished in one of several ways.
It can be cut off clean and perpendicular to the bore. This leaves little protection to the edge where the riflings are exposed and is not used by us.
It can have a recess cut into the middle section of the crown (see illustration). This is common on our centerfire rifles.
The crown surface can taper from the outer edge toward the bore itself to create a recess. An 11 degree angle would be a common crown design on some target guns.
Some even have additional angled surfaces inside a second crown.
The muzzle of our barrels have special crown designs to protect the rifling. Some have what are often called a "target crown." A target crown is specially machined into the muzzle to protect the rifling with the intent of preserving and protecting accuracy. If the very edge of the bore -- especially where the riflings are exposed -- is nicked, scratched or damaged in any way it can affect the dynamics of the bullet as it leaves the muzzle. Among target shooters it is usually explained that they desire target crowns and a clean edge to make sure that gas pressure on the bullet is released equally as the bullet leaves the muzzle. A clean crown also assures that the bullet is not scratched or altered in any way as it leaves the muzzle.
A recessed crown is a critical feature on any barrel. If riflings are damaged in any way, especially at the muzzle, accuracy suffers and it is often difficult for any shooter to determine the cause.
The image below shows a target crown that is recessed and carefully finished to protect the riflings and edge of the crown itself. The example shown is a Browning X-Bolt.
The Tech-Term "Recessed Crown" is referred to in the following products: