11 degree crown

[P-Zak]

I did a search but didn't find what I wanted to know, so...What is the benefit (if any) to the 11 degree crown. I know they look awesome but is there more to them?

Jason

[Toolguy]

There is no magic angle to a crown. The one requirement is it has to be concentric to the bore. If a crown is off center it will fling bullets all over. A little bit off will make the groups bigger. A lot off will make patterns like a shotgun. A flat bottom counter bore is the safest because it is 90 degres to the bore so if the outside ring of the counterbore is off a little the bullet will still exit the barrel evenly all the way around.

[P-Zak]

Thanks Warren, I thought so but have seen it enough to wonder.

[Steve RA]

Someone somewhere decided it was a lot better than a 10 or 12 degree crown so it became popular.

[Guy Neill]

If I recall from past reading, tests with 90º crowns (that can be easily damaged) showed that the gases exited at - 11º.

Thus, an 11º crown serves to protect the rifling, and allows the gases to flow in the direction they would naturally go anyway.

I don't recall where I read it as it was a long time ago, but that's how I recall it.

Guy

[P-Zak]

Thanks Guy,

I figured there must be a little bit of input from varying sides on this one. I knew there would be some in the, "cause thats what works" school and those who based it on some research somewhere. More curiosity than anything else...I got to thinking about a potential build and wondered what the actual reason for the crown cut was other than the appearance.

Jason

[toothguy]

If I recall from past reading, tests with 90º crowns (that can be easily damaged) showed that the gases exited at - 11º.

Thus, an 11º crown serves to protect the rifling, and allows the gases to flow in the direction they would naturally go anyway.

I don't recall where I read it as it was a long time ago, but that's how I recall it.

Guy

Guy, I found it interesting looking at pictures of Phillip Hemphill's PPC revolver built by Robert Jones. The crown is recessed and cut at 90 degrees like a rifle crown. I talked to Warren about this and he said the take home on the crown is that it is cut concentric.

[Guy Neill]

For best accuracy, the crown must be square to the bore. That doesn't always mean square to the end of the barrel. So, whether we call it concentric or square, it must match up. If it is not, the gases begin venting unevenly, and it must vent uniformly or it will disturb the bullet exit.

That is why recessed or other means are used instead of a flat 90º - to protect the bore exit from damage in the form of nicks or dings that will result in uneven gas venting.

Guy

[PatJones]

It is not uncommon for at least one of the grooves of a barrel to be slightly deeper than the others. It's usually only a half thousandth or less, but if the crown is cut at an angle that groove will release the gasses after the other grooves. This can kick the base of the bullet sideways as it exits the bore.

The flip side is that it is easier to damage a 90 degree crown. With a little care this isn't a problem though.

-pat

[JimmyZip]

Aren't there recessed target crowns that give you the best of both worlds though? I'm sure someone can post a pic of one. can't see why a barrel builder can't do it for you if they can do it on rifle barrels. Would look cool on a bull barreled pistol.

[PatJones]

The recess helps guard against objects bumping the crown but most crown damage I see comes from improper cleaning.

-pat

[toothguy]

The recess helps guard against objects bumping the crown but most crown damage I see comes from improper cleaning.

-pat

+1, I try to use a boresnake if possible.

Edited November 22, 2012 by toothguy

[toothguy]

For best accuracy, the crown must be square to the bore. That doesn't always mean square to the end of the barrel. So, whether we call it concentric or square, it must match up. If it is not, the gases begin venting unevenly, and it must vent uniformly or it will disturb the bullet exit.

That is why recessed or other means are used instead of a flat 90º - to protect the bore exit from damage in the form of nicks or dings that will result in uneven gas venting.

Guy

Guy, my first competition gun was a 625. Loved the gun but never shot very good groups past 15 yards. I just assumed it was due to the 4" barrel length, my loads or my lack of skill. I mentioned to Warren that the factory crown look unusual because it was thin on one side and thick on the other. Warren looked at it and kind of laughed saying lets fix that. He showed me that the factory had also cut the forcing cone at a non concentric angle as well. After re cutting both, my groups improved dramatically.