Air Gun Home :: View topic - Accuracy Differences Between 11 And 45 Degree Crown

Mark5043 · Silver Status Member

I see the 11 degree is referred to as a target crown.Does that mean it's generally more accurate than a 45?...If so why?I would think that if the crown is done properly,and is completely smooth,that there wouldn't be much of a difference?Is there any real difference in one or the other as it pertains to air guns?

rsterne · Moderator

I've never seen a crown done at 45 degrees.... although when you do it with a brass screw you are creating a bevel on the edge as you polish it....

The idea behind the 11 degree crown is that as soon as the base of the bullet clears the hole the gasses vent evenly and quickly to the sides so as not to disturb the bullet.... I have no idea why 11 degrees, I can only assume it was from experimentation....

If the crown was 90 degrees to the boreline it would be very susceptible to damage.... At 45 degrees, I assume the gasses disturb the bullet a great deal.... At 22.5 degrees, less.... at 11 degrees even less.... It may be no more complicated than being 1/4 of 45 degrees....

Bob

Mark5043 · Silver Status Member

Thanks for the reply Bob.The reason I ask is that I was looking at some crowning tools online...I'm thinking of trying my hand at some barrel work,such a doing a custom length,or something like that in the future,and frankly don't know enough about the subject yet to make an educated choice....looks like I need to do some more research.

Mark5043 · Silver Status Member

Here is something I was looking at....

http://www.brownells.com/.aspx/pid=628/Product/79-deg-MUZZLE-
CROWNING-CUTTER

rsterne · Moderator

I could be wrong, but I think the 45 degree is just to remove any burrs left by the 11 degree crowning tool....

Bob

Mark5043 · Silver Status Member

Okay I see now... looks like the 45 degrees I was talking about has to do with this Chamfering tool...

http://www.brownells.com/.aspx/pid=18298/Product/45-deg-MUZZLE-CYLINDER-CHAMFERING-CUTTER-BRASS-PILOT

Sorry about the confusion......... Embarassed

SMP · Silver Status Member

The 11 deg crown is really only found on piloted setups using hand driven cutters.
The slight angle does two things
a) protects the bore slightly
b) stabilizes the cutter during the operation

The very best crown is 0 deg for accuracy. Pope tested this ad infinitum.

A crown that offers accuracy and and a bit of protection is the "0 deg stepped crown".

radar · Silver Status Member

Lilke Bob, said, I think it was by experimentation, as the 11 degrees is sort of a nominal figure, and it may be off a degree or two from 11º.

And Sean is right (as usual Laughing

) about the 90º being ideal, but the recessed 90º is probably much more difficult to perform properly without a machine shop, and I would think best left to a professional gunsmith.
And here is a link showing both types, and the operation of hand-forming the 11º with the Brownell's tool:

http://riflestocks.tripod.com/targetcrown.html

rsterne · Moderator

I'll take your word on the 90 degree being the most accurate, it actually makes sense.... and recessing it to protect the edge of the bore also makes sense.... I set my lathe compound rest at 11 degrees, use a sharp HSS bit and turn from the bore outwards.... which works great as long as the bore is centered in the barrel.... Then I can claim to have an "11 degree target crown" which sounds wunnerful, don't it?.... Mr. Green

Bob

radar · Silver Status Member

SMP · Silver Status Member

It does sound awesome Mr. Green

Pope advocated polishing the metal to a bright finish before the final lapping. After a series of shots you can see the gas pattern in the polished metal. If the gas pattern shows even star shaped points the crown is good.

mtsheron · Member

I think the 11 degree crown is the inner cut and the industry std. so to speak, set aside from a 90 degree recessed crown. The 45 degree OD is the chamfer <??? outer angle around the barrel cut that is done if I have my reading; videos; and such understood correctly.

rsterne · Moderator

Most factory crowns I have seen are rounded, like half a donut.... and meet the bore at 20-30 degrees.... It protects the rifling well and looks nice I guess....

Bob

oddtodd · Silver Status Member

My dad has a 22 cal target rifle that has a stepped crown like that. I'll have to look next time I'm over there to see if it has a 90 degree or 11 degree crown.