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MarkG
03-29-11, 17:34
What is the significance of 11 degrees? Why not 10 or 12?
spdldr
03-29-11, 19:26
It appears that it is just a tradition. Possibly some barrel maker with an excellent reputation for accurate barrels used it.

The only objectives of a crown are to precisely square off the muzzle edge of the rifling in a burr free manner, and recess this cut to protect the edge of the rifling if the muzzle contacts something it should not.
Alpha Sierra
03-29-11, 20:03
I would think the angle makes absolutely no difference. It's just a way to recess the end of the rifling from the end of the barrel's outside diameter.

Some barrel makers make the "crown" more like a counterbore, which seems much more robust than a cone to me.
Kevin_J
03-29-11, 23:12
Some benchrest folks think that the 11 degree crown ports gas around the bullet in a way that better stabilizes the bullet. My own personal observation has been that a uniform crown is more important than the angle. Harold Vaughn took some photos of gas escaping from different crown types and didn't find a discernible difference.

I'll try to find some references and post them here.
mattmcg
03-29-11, 23:13
Confirmed. The degree of angle cut does not make a hint of difference for accuracy. The recessed target crown is simply to protect the crown from damage.

That said, when you recess the crown, you are reducing the effective barrel length of the weapon. It's only a minor fraction of course which is why it doesn't necessarily matter but a shorter barrel length will reduce velocity of the bullet, however slight.
AJS
03-31-11, 08:52
It may well make a difference with some projectile base angles in BR rifles but not in any normal rifle.
We want something that offers protection and is cut well.

The factions of an inch used to do a crown will not cause a detectable loss of velocity.
Throat length would make far more of a change.
Kevin_J
03-31-11, 10:12
It may well make a difference with some projectile base angles in BR rifles but not in any normal rifle.
We want something that offers protection and is cut well.

The factions of an inch used to do a crown will not cause a detectable loss of velocity.
Throat length would make far more of a change.

Agreed. I like a protected crown regardless of the the angle. Freebore jump can influence accuracy just about as much as a damaged crown due to bullet shaving when it enters the throat.