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Flat crown square to bore ?

I use 11 degree crowns for flat base bullets. Makes owner happy.
I use flat crowns for boat tail bullets. Makes target happy.
 
Early on in F Class builds I found a starburst pattern on 11 degree crowns. This told be that there is a turbulence with the gases off boat tailed bullets that hit the crown. Not wanting that gas to have a chance of upsetting the flight - I use only flat crowns.
Just my wild ass guess. But it works!
 
Kings X said:
Early on in F Class builds I found a starburst pattern on 11 degree crowns. This told be that there is a turbulence with the gases off boat tailed bullets that hit the crown. Not wanting that gas to have a chance of upsetting the flight - I use only flat crowns.
Just my wild ass guess. But it works!
Click to expand...
Exit velocity of the gas is 7-8000 FPS. The good news is the BC of the gas sucks and it doesn't go very far. Just a few inches in it's densest form. 3-4 inches in the videos I saw. The gas completely envelops the bullet as it deflects off the BASE and passes it. Not the bearing surface, the base. The gas will affect the bullet flight in some muzzle brakes. From past experience a brake with an expansion chamber over 1.125" long will allow the gas to pass the bullet then get deflected inward in front of the bullet.
 
look at post #1 and #24

Does the Rifle Move?

Don't read too much into the actual groups at this point but check out the very clear sine wave pattern on the target. This is a 100 yard test target. I'm not posting it to show that the groups are perfect or not, but that the sine wave is very apparent. Very good shooting at any rate.
forum.accurateshooter.com
 
DaveTooley said:
Exit velocity of the gas is 7-8000 FPS. The good news is the BC of the gas sucks and it doesn't go very far. Just a few inches in it's densest form. 3-4 inches in the videos I saw. The gas completely envelops the bullet as it deflects off the BASE and passes it. Not the bearing surface, the base. The gas will affect the bullet flight in some muzzle brakes. From past experience a brake with an expansion chamber over 1.125" long will allow the gas to pass the bullet then get deflected inward in front of the bullet.
Click to expand...
Dave,

Am I understanding the last sentence correctly, such that for a brake not to introduce inaccuracy, the expansion chamber should be quite short (way less than the 1.125”)?

Thanks for sharing such info. I’d not come across any discussions about this topic before.

I’m relatively new to chambering barrels and have only installed this one brake. This brake was from a member here around 2011, who was making & selling them. If I remember correctly, was he Ross? This rifle shoots fantastically; apparently the brake is doing no harm. The dowel I’m holding in the pic shows about where the crown is located.
6F672287-4692-49E4-94B9-6ECBF41A2B44.jpeg
 
BuffaloBill said:
Dave,

Am I understanding the last sentence correctly, such that for a brake not to introduce inaccuracy, the expansion chamber should be quite short (way less than the 1.125”)?

Thanks for sharing such info. I’d not come across any discussions about this topic before.

I’m relatively new to chambering barrels and have only installed this one brake. This brake was from a member here around 2011, who was making & selling them. If I remember correctly, was he Ross? This rifle shoots fantastically; apparently the brake is doing no harm. The dowel I’m holding in the pic shows about where the crown is located.
View attachment 1327036
Click to expand...
A brake with the bore just over bullet diameter doesn't have any problems. I found that a brake with an expansion chamber, meaning it usually was tap drill diameter, exceeding 1.125" could have problems with gas passing the bullet, hitting the end of the brake and then upsetting the bullet. I'm not saying it happens all the time but I've seen more than once. There is no reason to make a brake longer. The first row of holes does probably 80% of the work.
Just looking at yours I wouldn't be concerned putting one on a rifle.
 
I have a 300 yard range directly behind my machine shop. I have taken know 6ppc barrels and played with crown shapes and dialing in methods a bunch. I have a method I know use but my overall findings might surprise ya!
 
back in 2001 one better benchrest shooters I new. he was also a mechanical engineer took really good shooting 6mm ppc recrowned it three different times flat , flat with chamfer , and with a handheld 60 degree chamfer tool. and did a accuracy test. there were no changes to the agg. size . he did this because
the other experts said you couldn't use a hand tool and maintain accuracy . I've built a lot guns i'll
put any kind crown that the shooter wants . but for me I use a flat with a small chamfer. have fun life is short!
 
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