Barrel Crown, Chamfer and Accuracy

Matt_J · May 28, 2020, 01:13 PM

I have an Andro Co. Alpha16. It comes with a Ballistic Advantage Modern Series 16" Midlength Gas barrel (phew). The barrel crown has no chamfer, just a straight 90° cut.

My understanding is that a chamfer (11°, 45°, etc.) is to protect the crown from getting damaged, so that when gasses leave the barrel they will hit the crown uniformly on all sides. If the crown has damage on it, especially close to the bore, the gas will react differently in the damaged area and promote instability of the bullet.

So if this is true, the 90° cut on my barrel will remain accurate as long as it does not get damaged, which is ensured by the VG6 Gamma Comp that came on the rifle. Ballistic Advantage's Performance Series has an 11° "Target Crown" but offers the same MOA guarantee that the Modern Series does.

Is there something I'm missing about a chamfered crown as it relates to accuracy that it should be called a Target Crown or is it a marketing term? Also, is there a correlation between the angle the gas hits the crown and how it effects bullet travel, or does the uniform dispersion of gas around the crown only matter?

bfoosh006 · June 1, 2020, 07:11 PM

Correct... remember don't clean from the muzzle to the breach.

Matt_J · June 2, 2020, 06:02 AM

Thank you!

Bart B. · June 2, 2020, 07:35 AM

An eleven degree crown (face?) can improve accuracy about 1/20th to 1/10th MOA.

All the 7.62 NATO Garand barrels I wore out showed no accuracy degradation as the bore diameter at the muzzle opened up over .001 inch from bare steel cleaning rod wear. No copper wash the last half inch of the barrel. All tested about MOA at 600 yards after 3000 rounds. Rebarreled at about 3500 rounds. All had the standard 45 degree crown.

May 28, 2020, 01:13 PM	#1
Matt_J Member Join Date: May 21, 2020 Posts: 17	Barrel Crown, Chamfer and Accuracy I have an Andro Co. Alpha16. It comes with a Ballistic Advantage Modern Series 16" Midlength Gas barrel (phew). The barrel crown has no chamfer, just a straight 90° cut. My understanding is that a chamfer (11°, 45°, etc.) is to protect the crown from getting damaged, so that when gasses leave the barrel they will hit the crown uniformly on all sides. If the crown has damage on it, especially close to the bore, the gas will react differently in the damaged area and promote instability of the bullet. So if this is true, the 90° cut on my barrel will remain accurate as long as it does not get damaged, which is ensured by the VG6 Gamma Comp that came on the rifle. Ballistic Advantage's Performance Series has an 11° "Target Crown" but offers the same MOA guarantee that the Modern Series does. Is there something I'm missing about a chamfered crown as it relates to accuracy that it should be called a Target Crown or is it a marketing term? Also, is there a correlation between the angle the gas hits the crown and how it effects bullet travel, or does the uniform dispersion of gas around the crown only matter? Last edited by Matt_J; May 28, 2020 at 01:27 PM.

June 2, 2020, 07:35 AM	#4
Bart B. Senior Member Join Date: February 15, 2009 Posts: 8,927	An eleven degree crown (face?) can improve accuracy about 1/20th to 1/10th MOA. All the 7.62 NATO Garand barrels I wore out showed no accuracy degradation as the bore diameter at the muzzle opened up over .001 inch from bare steel cleaning rod wear. No copper wash the last half inch of the barrel. All tested about MOA at 600 yards after 3000 rounds. Rebarreled at about 3500 rounds. All had the standard 45 degree crown. Last edited by Bart B.; June 2, 2020 at 07:44 AM.

June 1, 2020, 07:11 PM	#2
bfoosh006 Senior Member Join Date: February 17, 2009 Posts: 1,089	Correct... remember don't clean from the muzzle to the breach.

June 2, 2020, 06:02 AM	#3
Matt_J Member Join Date: May 21, 2020 Posts: 17	Thank you!