11 Degree Muzzle Crown.

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11 Degree Muzzle Crown.

Post by Bigtrout on Mon Feb 08, 2016 3:59 pm

Today I learned about the new (to me) craze in crowning.  Has anyone done the full 11 degree crown on their BE guns?  My S&W 986 has one and prompted me to look into the reason.  Some explanations give the example of directing the blast gas in a direction to stabilize the bullet.   I'm sure you folks are way ahead of me on this curve but I'm wondering if it's worth the 1/2 hour of a smith's fee to cut that crown on my 1911.  Any merit there?  Thanks.
Dave

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Re: 11 Degree Muzzle Crown.

Post by Jack H on Mon Feb 08, 2016 5:06 pm

11 degrees has been what I believe as the standard for a long time.  But curiously there are many muzzles relieved with a small 45 degree cut.  Even some top guns. 


I do believe most of us should nit pick on our fundamentals more than our equipment.  I also believe I should follow my own advice.

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Re: 11 Degree Muzzle Crown.

Post by Wobbley on Mon Feb 08, 2016 8:48 pm

11 deg came from rifle shooters.  Why 11 is a mystery.  But it works so people use it.  I'm  not sure that the relatively thin wall of of a 1911 barrel it can have any effect on channeling exiting gas but it does make for a good crown.

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Re: 11 Degree Muzzle Crown.

Post by r_zerr on Mon Feb 08, 2016 9:01 pm

The 11 degree came from tests that the AMU ran "way back when," with rifles (pre-1980 at least as this was when one of my first rifles was re-barreled), and the belief (probably not worthy of theory status) is that it has something to with the gas exiting.  The bigger issue to be addressed in crowning any barrel is how true to the axis of the bore is more of a consideration than the angle.

Further discussion could become one of which oil to use, or that of gun cleaning practices. Smile   If it works for you, it is the best!


-ron

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Re: 11 Degree Muzzle Crown.

Post by Jerry Keefer on Tue Feb 09, 2016 11:34 am

Muzzle blast... is the problem..and has been studied by numerous researchers. It's very interesting, and not as simple as imagining a water flow.
The area of the muzzle or transitional region is where internal pressures/ballistics become external. The gases rapidly expand and easily exceed the speed of the projectile, passing it,  while forming and creating complex patterns of vortex rings, various jet flows, mach disks, expansion fans, and shock waves.. each having its own effect on the bullet.   
Because extreme handgun accuracy has been my passion, I tried to find out as  much as I could on crowning.. Read many studies.. My conclusion, and that of the bench rifle community, is the crown must be zeroed on both of its axis to be as effective as possible.. The in depth studies done in science labs, conclude that the gas flow does not duplicate itself from shot to shot which changes the force. So each projectile is subjected to a different degree of influence from the pressures.
The crown angle seems to be less important than the zero of both axis.  Crowning of short pistol barrels requires a spider, and rifle barrels require a lathe spindle with a rear spindle spider.  Faster powders have less impact at the transitional zone than slower powders, because the pressures are dropping off quicker from the combustion of the faster burn.. Small base bullets, boat tails, etc. are also effected less, because of less area exposed to the pressures.. So, the answer is..???? Do the best you can when machining the crowns and this is one small reason different powders produce different results at the target..

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Re: 11 Degree Muzzle Crown.

Post by Bigtrout on Tue Feb 09, 2016 12:04 pm

Outstanding explanation, Jerry.  My gunsmith (mostly long guns) friend has a very precise kit for this cut he obtained from Brownells for a non-trivial sum.  I want to take my time on this one for it will void my warranty.   He's done many hunting and target rifles and most all gained a significant reduction in group size.  So it sounds good in principle but your statement on fast burning powder (e.g. 9mm) is a good argument for me to proceed with caution.  Thank you.

Dave

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Re: 11 Degree Muzzle Crown.

Post by Jerry Keefer on Tue Feb 09, 2016 12:21 pm

There is even debate as to the area of zero.. Is it the lands, or the grooves..of course taken from a zero bore axis..Hand driven, piloted reamers work from the land or bore size.. I am a groove guy.. both methods work far better than nothing. I bring my bores to zero, and then reach in with a long tenths indicator probe and re zero off the grooves.. Many bench rest machinists do that..Some don't.. It's like politics and religion debates..Smile
One thing it definitely reveals when done on a factory barrel.. Is how far out the factory crowns are.. It's amazing..

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Re: 11 Degree Muzzle Crown.

Post by Ed Hall on Tue Feb 09, 2016 2:01 pm

Can I ask this question in an understandable to all of us manner? Let's try!

Has there been study done in regards to whether a flat (cone) crown differs from a radiused crown?

Flat crown meaning a straight surface from muzzle to bore; radiused meaning concave, like using a large ball bearing to shape the crown, or convex, the opposite of the ball bearing?

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Re: 11 Degree Muzzle Crown.

Post by Jerry Keefer on Tue Feb 09, 2016 4:08 pm

Ed Hall wrote:Can I ask this question in an understandable to all of us manner? Let's try!

Has there been study done in regards to whether a flat (cone) crown differs from a radiused crown?

Flat crown meaning a straight surface from muzzle to bore; radiused meaning concave, like using a large ball bearing to shape the crown, or convex, the opposite of the ball bearing?
Hello Ed,
Some of the material I cited above is from a book/study done by a rifle enthusiast who happened to be a Supervisor of Aeroballistics and flight mechanics of nuclear ordnance.. Ground floor engineer for smart bombs and rockets.. He not only had the education, but the labs and scientific apparatus to do sensitive testing.. 
The shape of the crown has less effect than its mechanical zero..the  gases take the path of least resistance in all directions in micro seconds..I am surprised the bullet escapes with so little disruption..I does not appear, that trying to deflect or control the path of the gases is possible by crown shape, mainly because they are erratic and asymetrical.
We have little control over the ballistic event. But, we can control mechanical dimensions to within 5 digits with care..Some claim more, but most can't.
Now, when Precision Shooting was still in print, a rifle shooter claimed and showed groups that improved with a very deep crown.. But that was not based on a true testing procedure.. I have not read anything proving that claim since..
Very few smitihs bother with  a two axis crown or chamber. So for most folks, it has little concern..

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Re: 11 Degree Muzzle Crown.

Post by fc60 on Tue Feb 09, 2016 6:37 pm

Greetings,

After a trip to the range testing a new barrel in the "barrel tester", it is interesting to look at the soot, or lube star, at the muzzle after a test session.

Use a magnifying glass, if needed, and examine the pattern of the lube star. Barrels that have shot well for me, 10-X at 50 yards, display a very uniform distribution of soot. You can even count the number of lands and grooves easily as the star pattern highlights them.

I tend to follow Mr. Keefer's approach to the crown. Out comes the tenths indicator and a lot of tapping and adjusting to get things running true. I finish the crown with a solid carbide boring bar, for rigidity, and a sharp new insert with positive cutting geometry. I get the best results feeding from inside the bore to the outside.

I have used the magic 11 degree in the past and now I have migrated to the 45 degree crown angle. I feel it offers a bit more protection to have it recessed a bit more. Group wise, I cannot tell any difference between the two.

Factory crowns bring back a fond memory. We had a barrel that would not stay on the repair center at 50 yards when mounted in the barrel tester. My friend took it home and recut the crown discovering it was not quite true. Retesting with R-P TargetMaster (it was a 45 ACP barrel) the resulting ten shot group fit inside the X-ring at 50 yards.

Cheers, and thanks for the memory,

Dave

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Re: 11 Degree Muzzle Crown.

Post by C.Perkins on Tue Feb 09, 2016 7:36 pm

I have always examined the powder burn residue on the muzzle of my precision rifles.
The most accurate ones have a very uniform pattern.
A while back I built an AR15 using a 24" Lija 4 groove barrel.
It is the most accurate rig I have ever owned to date.



I know, I know, it is a rifle but I like it Smile

Clarence

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Re: 11 Degree Muzzle Crown.

Post by Ed Hall on Tue Feb 09, 2016 10:57 pm

HI Jerry,

My original 208s from the factory used to have a (six point) pattern similar to the one Clarence is showing, although not near as clean.  (Nice picture, Clarence!)  But the pattern got sloppy and so did the groups.  Larry instructed me to mount the gun in a heavy vice, via the barrel, and see what it printed.  I went a tad further and mounted the vice to a quarter-inch thick piece of plate aluminum on top of piece of 2x6 plank and drove the rear wheel of my Montero up onto the aluminum as it sat on the cement floor of the range.  I then mounted the 208, via the barrel, as directed by Larry, in the vice and tested several lots of .22, with the best (Eley Tenex, probably) only giving me about three inches at 50 yards.  It was suggested that I try recrowning, since the pattern was degraded and it underwent a recrown by USAMU and then a retouch by Larry.  The crown had become quite deep by the end of all this and there never was another pattern of any kind and I never did get anything like a tight group from it.  That was when I sent the barrel off to Alex to be relined, per your suggestion and you saw the one hole 50 ft group it produced upon return.  I still haven't set it up at 50 yards, but I'm quite confident it will print groups, since after the work I was able to get some 50 yard cleans again - something I'd been missing for awhile, prior to the reline.

Thanks much for all your help.  Looking forward to seeing you in the coming season.

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Re: 11 Degree Muzzle Crown.

Post by Colt711 on Sun Feb 14, 2016 10:27 pm

More yrs ago than I care to remember iI bought a used Colt Commander which had been accurrized and customised. A neat pistol. Getting it home I noticed the barrel, a 6" Colt in the Commander, looked as if it had been cut off by a nervous blind man usung a dull reciprocating saw. And the BoMar rear was adjusted far to the right. Bought @ Perry I had time to return it so went to the range first. Surprisingly, it shot very well.

I soon found w/ factory velocities it needed the sight setting mentioned. With my BE loads the sight was set normally. I thought it to be the crown. We trued the barrel on a friends lathe, crowned it. The result? Nothing!

Any ideas?

Ron habegger

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Re: 11 Degree Muzzle Crown.

Post by jglenn21 on Mon Feb 15, 2016 11:43 am

I believe it was Charlie Sisk a well know rifle smith, who tried to see what effect a beat up crown would have.. he purposely dinged and beat on the crown of a barrel and shot it comparing to the barrel with a good crown... basically nothing happened... doubt this proves much one way or the other, as I certainly have seen improvements on rifles by renewing the crowns myself.. I re-crown every Rem 700 barrel I don't replace without hesitation...really not good from the factory..


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Re: 11 Degree Muzzle Crown.

Post by Jerry Keefer on Mon Feb 15, 2016 12:06 pm

A certain swat team once had an H&K 94 rifle with the long barrel.. An enterprising armorer shortened the barrel with a hack saw and cleaned it up with a file.. this was in an effort to make the rifle more suitable for entries/CQC.
The gun would not hold a B27 target at 25 yards..
Gun was brought to me. The barrel was removed and an indicated crown was cut..
Instant tack driver... As I mentioned above,  the most hostile environment the projectile is exposed to, is the transitional zone from internal to external ballistics.. I assure you that the super record long range groups being shot today, are partly a result of precision machining in all areas..no least of which is the crown. The inter net is rife with claims that a brass, round head screw, coated with valve grinding compound, and driven by a hand held portable drill produces the ultimate crown.. To each his own..

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Re: 11 Degree Muzzle Crown.

Post by Ed Hall on Mon Feb 15, 2016 12:31 pm

Jerry Keefer wrote:...
The inter net is rife with claims that a brass, round head screw, coated with valve grinding compound, and driven by a hand held portable drill produces the ultimate crown.. To each his own..
So an embedding type compound is better, then!  Good to know! lol!

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Re: 11 Degree Muzzle Crown.

Post by Bigtrout on Mon Feb 15, 2016 1:48 pm

Ed Hall wrote:
Jerry Keefer wrote:...
The inter net is rife with claims that a brass, round head screw, coated with valve grinding compound, and driven by a hand held portable drill produces the ultimate crown.. To each his own..
So an embedding type compound is better, then!  Good to know! lol!
Yeah.  I read the hand held drill suggestion somewhere online.  It sounded it would result in a pretty non-concentric crown with an oblique axis and dubious proportions.  Some of the rifle folks are bringing their 11 degree crown to a high polish and claiming better groups.  I'm leaning toward not having the 11 degree crown done on my RO9 and waiting until someone else reports 1911 pistol results after doing so.  Anyone out there?

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Re: 11 Degree Muzzle Crown.

Post by Jerry Keefer on Mon Feb 15, 2016 2:50 pm

I have had many winning PPC revolvers and 1911s with 90 degree, flat face crowns... The key seems to be clearing the muzzle face perfectly/equally around the bullet base circumference.

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Re: 11 Degree Muzzle Crown.

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