Pointed Crown for rifle barrel

[LC Tikka]

Looking for your comment on this POINTED CROWN concept.

As we know the gas flow from the crown can influence accuracy, particularly for reverse angle and protruding crowns if not concentric to the bore.
So the less gas acting on the bullet base as it departs the barrel the better, I say.
Would this type of crown have benefits?
PS: The attributes listed below the sketch are not proven, but probable.

 

[DaveTooley]

Looking for your comment on this POINTED CROWN concept.

As we know the gas flow from the crown can influence accuracy, particularly for reverse angle and protruding crowns if not concentric to the bore.
So the less gas acting on the bullet base as it departs the barrel the better, I say.
Would this type of crown have benefits?
PS: The attributes listed below the sketch are not proven, but probable.

View attachment 993943

No it wouldn't. Velocity of the exit gasses are in the range of 6000 to 8000 FPS and briefly pass the bullet. The only thing that might help, and this is doubtful, is a brake that wipes the expanding gas off the bullet very close to the muzzle. Also I don't believe you can shoot the difference. Changes in muzzle pressure can be measured with Doppler radar because it can affect the flight of the bullet but that doesn't mean it's not accurate, just different.

 

[rardoin]

Other factor affecting the bullet at exit may be operable in the 'pointed crown' barrel. Reducing the diameter of the crown at the muzzle may cause increase in the bore diameter at the time of bullet exit as the wall diameter will be considerably thinner but subject to the same pressure as a standard muzzle. Some more theoretical implications to toss into the mental masturbation.

 

[joshb]

Hmmmmm. Hows about porting the barrel? Wait, that's been done.

 

[watercam]

Do a test. Start with the 'conventional' 11º crown (touted as best for boat-tail bullets and pretty standard on match rifles) and shoot multiple groups. Re-cut to your version of a crown on the same barrel and re-shoot the test. Should be minimum of ten five shot groups I would think. Get your target past 200 yards.
Best case scenario you are correct and revolutionize the industry, worst case you end up re-cutting back to a conventional crown with minimum barrel length lost.
Let us know!

 

[Ggmac]

It's been done , US military 1919 browning MG and the ma deuce , I think .
There's nothing that can be done to a crown that hasn't been tried already .
A good read is in precision shooting magazine and Rifle Accuracy Facts by H Vaughn .

 

[BoydAllen]

Some time back, there was an article in Precision Shooting magazine in which the author presented accuracy results from various crown configurations, shot with the same, rifle, barrel, and ammunition. At the end she rather wisely (IMO)commented that the differences in results were likely tuning effects that came from changes in the barrel's length rather than different styles of crowns. This is the sort of thing that would require a good tunnel (not all are) and a well built rail gun, and several barrels to evaluate. I am not holding my breath for that.

 

[Alex Wheeler]

Fluid dynamics. Thats not the way it works. Gasses will not come backwards after leaving the bore because the crown is pointed. The best way to direct gasses away from the bullet with a crown would be the radiused crowns you see on .22 rimfires. Sharp edges will cause the gas to shear and maintain its course. Radius' will allow gasses to follow the surface. At that velocity I dont know if this even applies. A simple test to show this, turn on the faucet and touch the edge of the running water with a finger. See what happens to the stream under you finger.

 

[RemingtonAI]

Fluid dynamics. Thats not the way it works. Gasses will not come backwards after leaving the bore because the crown is pointed. The best way to direct gasses away from the bullet with a crown would be the radiused crowns you see on .22 rimfires. Sharp edges will cause the gas to shear and maintain its course. Radius' will allow gasses to follow the surface. At that velocity I dont know if this even applies. A simple test to show this, turn on the faucet and touch the edge of the running water with a finger. See what happens to the stream under you finger.

AH Ha! I did the finger under the water test and I have concluded there could be an advantage to screwing one of those water sprayer things the kids play with in the yard, onto the muzzle of a rifle. I studied up on fluid dynamics and the theory is good to go. All I need is some sun tan lotion, safety goggles, and one of those adds on Home Shopping. This is going to be HUGE!

 

[savagedasher]

I was told a flat to 11degree was the most accurate . . Larry

 

[Eddie Harren]

I was told a flat to 11degree was the most accurate . . Larry

I was told ,"Your check is in the mail".

 

[Alex Wheeler]

The 2 best shooting rifles I have seen have crowns on opposite sides of the spectrum . both of them hold records, one has a zero degree the other a 45

 

[RonAKA]

I think the most important factor is that the bullet tail exits the barrel at the same time all around the circumference. One of the issues in making that happen with a beveled crown (in either direction) is making sure the crown cut is concentric with the bore. That is where the merit of the flat surface "crown" comes in. Your tool does not have to be concentric with the bore or the OD of the barrel. You just cut straight across. I suspect that is why Savage uses the flat crown method. Set up cost is low, and quality control is easy.

 

[Canadian bushman]

Fluid dynamics. Thats not the way it works. Gasses will not come backwards after leaving the bore because the crown is pointed. The best way to direct gasses away from the bullet with a crown would be the radiused crowns you see on .22 rimfires. Sharp edges will cause the gas to shear and maintain its course. Radius' will allow gasses to follow the surface. At that velocity I dont know if this even applies. A simple test to show this, turn on the faucet and touch the edge of the running water with a finger. See what happens to the stream under you finger.

^^^This is my thinking.

Somewhere between 3 and 10ksi (depending on cartridge and barrel) of hot gas leaving a long small hole. The majority of the gas is going forward. What little bit you can encourage in other directions via crown angle is of little difference. More or less not inducing additional turbulence is what you are after. I.E. a clean, perpendicular, undamaged, crown.

Muzzle breaks and suppressors will clear the "dirty air" from a bullets path more significantly than a change in crown angle ever could, and will show itself as a rise in MV. More so with suppressors because the pressure is staying behind the bullet a little longer.

For what its worth, in the limited playing ive done with crowns, i stop getting distinctive rifled soot on the crown when i cut steeper than 11 degs.

 

[LC Tikka]

Thanks for the responses.
It is understood that having a pointed crown will not magically turn these very high pressure gases on its own. A brake will divert gas but that is after the crown and would disturb the gas behind the bullet even more.

This is my theory on a pointed crown.
The idea of the pointed crown is to achieve a steadier release of the bullet.
In the split second a bullet leaves the barrel, the only obstacle preventing the gas from travelling forward is the bullet base, in this instant the HP expanding gas exiting the barrel cannot go forward to escape to the atmosphere. So a fair percentage of the gas will travel outward to lose the stored energy.

With a pointed crown the path the gas takes is less restrictive than a flat or recessed crown, so the effect of the escaping gases on the bullet would be reduced.

 

[ranch23]

LC, experimentation is how we learn new things.

 

[WSnyder]

Harold Vaughn proposed that reducing muzzle gas pressure reduced group size. One of his experiments was to vent the barrel just before the muzzle. He bored what was similar to a radial brake with holes along the rifling grooves with no counter bore, chamber or baffles. The bullet is supported all the way to the muzzle and gasses are bled off before the bullet exits. His experiment claimed a 35% average group size reduction (from .350" to .230") in his 6mm Remington rail gun. I've never heard if anyone ever tried repeating his results.

 

[SBS]

Would a pointed crown reduce recoil, as the barrel has less surface for the gases to push against?

 

[Dusty Stevens]

No. The gas will escape with the bullet the same as a flat crown. Only difference is it would shoot horribly im sure. Recoil is not a reaction to gasses hitting the crown.

 

[swd]

Would a pointed crown reduce recoil, as the barrel has less surface for the gases to push against?

That is one of theories of this type of crown. But if there were really an advantage we'd all be doing it.
As far as the the most accurate type of crown, flat, 11deg, etc, the most concentric at the tightest part of the barrel wins every time no matter what the other variables are.