Crowning

[Shanks]

First off hello, Long time reader first time poster. Read a good chunk of this forum and find it very appealing as a technical form. I'm a "new" machinist. I also like to play gunsmith but those damn tiny peices always screw me over.

Earlier today while reading though the post on all ti and 17 4 ss i found this link: http://www.ivorbittle.co.uk/Books/Fluid ... bullet.htm

It got me thinking about the radial expansion of gas around the muzzel and behind the bullet exiting. I was always taught by gunsmiths that for a firearm to be accurate a good, clean and often recessed crown was needed. So if darn near all barrels that are crowned have am 11° crown (?) and threads on the od, what if you took that crown and cut it at 60° like baffles are often cut at to aid in suppression? Has anyone gotten to experiment with this idea?

Thanks,
Shanks

[silencer_kid]

"11" is the nickname, 79 degree is the actual cut.

you get some stability advantages by releasing the gases along a angled path vs the hard 90. concentric is very important too, if you crown it should be concentric to the muzzle edge, etc.

does this help when silencer is attached? maybe, depends on if the silencer itself will negate the effects of the muzzle crown. crowning cant hurt, but concentric is nearly impossible when the end is threaded (w/o an end piece attached, a chamfer can help here before crowning, etc). you could crown it with the end cap attached (so that inside of cap is flush with end of barrel) before the end cap goes onto the can, etc. data for all this, likely non-existent.

[Shanks]

Please excuse the crude drawing

http://imgur.com/cY2BwhD

White is the barrel
Red is the cans tube and what i will for now call a deflector
Yellow is the flight path of the bullet
Blue is the baffles

My thought was that if one can control the initial flow the gas you may be able to make an incredible amount of backpressure and turbulence. The space between the muzzle and deflector could be from 1 to 4 inches, im not really sure lf the efficiency of the crown for redirecting the gases much past making them escape in a circular path. Im also not sure what and extreme angle would do to the flight path

[300sniper]

On a threaded barrel I do a 60° included angle break at the bore/rifling and then 169° included angle (11°) toward the OD then finished with no taper to the OD.



On a non-threaded barrel, I do a 60° included angle break at the bore/rifling and then a .090" deep recessed crown with a 90° included angle taper out to the end.



Neither of these methods have anything to do with accuracy. It is just a way to protect the crown from damage.

[T-Rex]

I think it would be best if you took a look at some cutaways with muzzle brakes/flash hiders involved.
You don't need any extravagant crowning, just some threads.
The muzzle device design will cause serious, initial, turbulence and, when coupled with blast chamber configuration, can seriously impact the areas your specifying.

[silencer_kid]

Neither of these methods have anything to do with accuracy. It is just a way to protect the crown from damage.

absolutely false. you might argue the diff in accuracy, but if you like i can point you 1,000 different ways to why crowning is also tied to accuracy.

i prefer to crown the 45 degree all the way out to barrel edge (if it allows it, depends on if its a crown cutter or you have it on a lathe, etc), as long as bore to OD is concentric, etc, otherwise stop in a tad, or machine concentric


here's 1 of 1,000+
http://yarchive.net/gun/barrel/barrel_crowning.html


and your 1st pic of the concentric crown with threading is what i was talking about, but it has to be specifically machined that way. run-of-the-mill threaded barrels are not like that.


the "target" crowns are preferred for accuracy

[300sniper]

Neither of these methods have anything to do with accuracy. It is just a way to protect the crown from damage.

absolutely false. you might argue the diff in accuracy, but if you like i can point you 1,000 different ways to why crowning is also tied to accuracy.

I cut my muzzles shapes to protect the edge of the bore, pure and simple. The threaded muzzle is less dramatic than the non-threaded because chances are, it will have a muzzle device on most of the time to protect it and the limited real estate available. I cut them concentric to the bore within .0002" TIR or better for accuracy. I am not sure how you can say that my statement was false.

I have cut about every type of crown under the moon and I promise you, you would not be able to tell the difference on target between a 90° and 79° on anything short of a dedicated benchrest rifle, if you even could then. You cannot say that a 79° (11°) is going to be the most accurate crown angle for every rifle/every caliber/every load/every day.

[Tony M.]

I am not sure how you can say that my statement was false.

Don't worry about silencer squid. He's a troll who lives in his mothers basement.

[300sniper]

Posting just for fun:

http://www.youtube.com/watch?v=MPv5N3rIhgk

http://www.youtube.com/watch?v=GQCKK_m4Xq8

[Capt. Link.]

Don't worry about silencer squid. He's a troll who lives in his mothers basement.

You mean "Skippy" I like him to come into my shop and ask for a 79* crown he'll get one.

The 11 degree was adopted as a standard where there was none.A recessed crown is just to add protection to the lands & grooves from impact.A perfect crown always helps accuracy and looks better than a standard rounded factory job.

Welcome aboard the waters are turbulent!

[T-Rex]

You mean "Skippy"

Yes, I believe he was referring to Skippy!

[silencer_kid]

Neither of these methods have anything to do with accuracy. It is just a way to protect the crown from damage.
I am not sure how you can say that my statement was false.

A perfect crown always helps accuracy and looks better than a standard rounded factory job.

have at it, my popcorn is made. both of the target crowns, one of which you show, does help accuracy. i do not prefer the recessed crown, but my 22mag ss bull has that from factory, so for now i leave it alone.

the degree is measured up off of bore axial, not a -11 from +90. i guess 11 sounds better than 79, or 11 prints better, not really sure.

so if you are backwards, its 101, if forward its 79.

[Capt. Link.]

Neither of these methods have anything to do with accuracy. It is just a way to protect the crown from damage.
I am not sure how you can say that my statement was false.

A perfect crown always helps accuracy and looks better than a standard rounded factory job.

have at it, my popcorn is made. both of the target crowns, one of which you show, does help accuracy. i do not prefer the recessed crown, but my 22mag ss bull has that from factory, so for now i leave it alone.

the degree is measured up off of bore axial, not a -11 from +90. i guess 11 sounds better than 79, or 11 prints better, not really sure.

so if you are backwards, its 101, if forward its 79.

Gunsmiths settled on 11* a hundred years ago and were supposed to listen to you.

[silencer_kid]

Gunsmiths settled on 11* a hundred years ago

yeah, i laugh at it to, wondering if the moonshine got in the way there.

11 degrees from what exactly, oh, right, 11 degrees from a perpendicular to bore axial. ah, yes, a perfectly klugy measurement spec. almost like saying "731 degrees". since the cut is concentric to bore axial (a conundrum in math btw) the angle is axial referenced, not referenced from another line. ah, too much math here, who am i kidding, nevermind, it 11 degress.

[300sniper]

have at it, my popcorn is made. both of the target crowns, one of which you show, does help accuracy. i do not prefer the recessed crown, but my 22mag ss bull has that from factory, so for now i leave it alone.

the degree is measured up off of bore axial, not a -11 from +90. i guess 11 sounds better than 79, or 11 prints better, not really sure.

so if you are backwards, its 101, if forward its 79.

"Helps accuracy"? What experimentation have you done personally to prove that a "target crown" helps accuracy over a simple crown cut perpendicular to the bore? How were the results measured?

[Capt. Link.]

The reason its 11* is because that's the way a compound is graduated.You are either parallel at zero or at a angle to the centerline of the lathe.The use of standard terms is to help communication not hinder it.

[silencer_kid]

have at it, my popcorn is made. both of the target crowns, one of which you show, does help accuracy. i do not prefer the recessed crown, but my 22mag ss bull has that from factory, so for now i leave it alone.

the degree is measured up off of bore axial, not a -11 from +90. i guess 11 sounds better than 79, or 11 prints better, not really sure.

so if you are backwards, its 101, if forward its 79.

"Helps accuracy"? What experimentation have you done personally to prove that a "target crown" helps accuracy over a simple crown cut perpendicular to the bore? How were the results measured?

my own 1911 45, thats how. about 20yrs ago when i got my 1911 i was on fence for doing the crown, so i did it, results are better.
my savage ss 3006 shoots ballistic tip just fine to 300yds on oem cut
my 22mag ss bull shoots ballistic tip boat tail just fine past 200yds on oem recessed crown
so for these two rifles i did not see a need for better accuracy, not for their use. 1911 needed some improvement.

and your testing showing wasted time on crowning for accuracy?

[300sniper]

have at it, my popcorn is made. both of the target crowns, one of which you show, does help accuracy. i do not prefer the recessed crown, but my 22mag ss bull has that from factory, so for now i leave it alone.

the degree is measured up off of bore axial, not a -11 from +90. i guess 11 sounds better than 79, or 11 prints better, not really sure.

so if you are backwards, its 101, if forward its 79.

"Helps accuracy"? What experimentation have you done personally to prove that a "target crown" helps accuracy over a simple crown cut perpendicular to the bore? How were the results measured?

my own 1911 45, thats how. about 20yrs ago when i got my 1911 i was on fence for doing the crown, so i did it, results are better.
my savage ss 3006 shoots ballistic tip just fine to 20yds on oem cut
my 22mag ss bull shoots ballistic tip boat tail just fine past 200yds on oem recessed crown
so for these two rifles i did not see a need for better accuracy, not for their use. 1911 needed some improvement.

and your testing showing wasted time on crowning for accuracy?

So one pistol had an improvement with a re-crown. Was that due to the angle or due to it being freshened up?


Again, I have cut barrels on precision rifles for people that shoot precision rifles with many different crown shapes/angles. I have not seen one difference in accuracy from any of them.

I never said putting a clean/concentric crown was a waste of time. I am simply saying you will not shoot the difference between an 11° and a flat crown, if they are both done correctly.

[Kanook]

my savage ss 3006 shoots ballistic tip just fine to 20yds on oem cut
my 22mag ss bull shoots ballistic tip boat tail just fine past 200yds on oem recessed crown
so for these two rifles i did not see a need for better accuracy, not for their use. 1911 needed some improvement.

and your testing showing wasted time on crowning for accuracy?

A 3006 at 20yds and a 22mag at 200yds

[whiterussian1974]

A restatement of the OP might be: Why is 11* (from perpendicular) the best angle for preserving accuracy? Why not 30, 45, or 60*?

[Capt. Link.]

So one pistol had an improvement with a re-crown. Was that due to the angle or due to it being freshened up?


Again, I have cut barrels on precision rifles for people that shoot precision rifles with many different crown shapes/angles. I have not seen one difference in accuracy from any of them.

I never said putting a clean/concentric crown was a waste of time. I am simply saying you will not shoot the difference between an 11° and a flat crown, if they are both done correctly.

Bingo

[silencer_kid]

So one pistol had an improvement with a re-crown. Was that due to the angle or due to it being freshened up?

my 1911 oem muzzle was fairly straight and concentric. not sure if 79 or 60 would have made a diff between the two angles, but definitely better than the oem cut.

[Historian]

Video of Ray Brandes crowning his joy-to-own
Bully Barrel for S&W 41:

<< https://www.youtube.com/watch?v=fSzXNlQ97VI >>

And once the HPA passes ...

[Samson1044]

Neither of these methods have anything to do with accuracy. It is just a way to protect the crown from damage.

absolutely false. you might argue the diff in accuracy, but if you like i can point you 1,000 different ways to why crowning is also tied to accuracy.

i prefer to crown the 79 degree all the way out to barrel edge (if it allows it, depends on if its a crown cutter or you have it on a lathe, etc), as long as bore to OD is concentric, etc, otherwise stop in a tad, or machine concentric


here's 1 of 1,000+
http://yarchive.net/gun/barrel/barrel_crowning.html


and your 1st pic of the concentric crown with threading is what i was talking about, but it has to be specifically machined that way. run-of-the-mill threaded barrels are not like that.


the "target" crowns are preferred for accuracy

If someone left a finish like that on the crown of my rifle id be PISSED , I'm good friends with Don Geraci who is an gifted rifle builder and shooter (several world records to his name) all of his personal target guns have a recessed flat crown. I've discussed this with him and his opinion is that as long as the crown is concentric to the bore all the way around it doesn't matter the angle. He has been in the Bench Rest shooting crowd longer than a lot of us have been alive and shot with some of the best in the world so i'm certain that if there was some specific angle he would be using it. That like saying that the 1-11.25 rate of twist holds some magic for the 308 bore , its just silly. I've seen some pics of "300sniper" work and seen him talk about his methods of machining (snipers hide)and I would not hesitate to have him build a rifle for me that I expected to compete with , he has made enough chips to know what he is doing and talking about
I personally prefer a flat recessed crown and 60 degree to just break the lip of the bore. I crown barrels the exact same way weather its to be threaded for a brake or suppressor.

[silencer_kid]

If someone left a finish like that on the crown of my rifle id be PISSED ,

you do know that was a pic just showing the various crown types, right?

i guess Don Geraci is not in the majority group that say angled crown is better than 90.

most will tell us
"11 degree is standard, recessed or not. it is optimal in terms of reduction of instability in flight caused by gas blow by at the moment of the bullet's exit from the muzzle"

and

"11 degree crown is supposed to be the most accurate, at least in a rifle. It was tested and developed by benchrest shooters, who are guys that spend lots of time and money trying to put 5 rounds into 1 hole."

how much more accuracy do you get can be debated until man lands on Venus.