Gunsmithing Want to learn about crowns...
- Thread starter misparkz
- Start date
Re: Want to learn about crowns...
It's the one last chance for the gun to have any effect on the bullet. I think you can agree it should be all it can be.
It's the one last chance for the gun to have any effect on the bullet. I think you can agree it should be all it can be.
Re: Want to learn about crowns...
ok points taken but spell it out a little more for me... I've got a lot to learn.
WHAT effect does it have on the bullet? How do the different degrees or profiles of the crown effect or affect the bullet differently? What makes one crown better than another?
ok points taken but spell it out a little more for me... I've got a lot to learn.
WHAT effect does it have on the bullet? How do the different degrees or profiles of the crown effect or affect the bullet differently? What makes one crown better than another?
Re: Want to learn about crowns...
In a modern high performance centerfire cartridge, chamber pressures peak out as much as 60,000 CUP (Copper Units of Pressure)
How this translates into regular PSI I have no idea, but suffice to say it's a chitload that'll melt your face off if you don't build the gun right.
Ok, so several tons of "steam" behind the bullet. The projectile is accelerated from a dead stop to 2+ times the speed of sound in less than a meter of travel. In addition it's accelerated from a dead stop to upwards of 300,000 RPM in the same distance.
Lots going on there with powerful forces at play.
When we transition from supported motion to free flight it takes place at the muzzle. We want a clean transition with no influence on the bullet as it begins to fly. A proper crown (and there can be some variation on exactly how it ends up looking) will provide a clean/radial dispersion of the gas charge while at the same time offering zero influence on the bullet.
If the crown is cut "cockeyed" for instance, (meaning if you were to do something really foolish and cut it at 20* angle with a hacksaw) the gas on the trailing edge would meet the atmosphere before the opposite side. This would influence the exit and potentially ruin/degrade the accuracy.
A concentric edge free of machine/tool marks promotes better accuracy. The exact relief angle can be fiddled with to a certain point with basically no change.
Years ago (1950's) the US Army conducted a study on this subject. It was found that 11*'s offers the best accuracy. It's since become a cardinal rule of sorts. That being said there's a great many guns with 90* crowns that will get scarey small on paper. 90* crowns are far less work to machine because they don't require any real setup. Just stick it in the lathe and go. 90* is square regardless of how much the bore is jump roping around.
The second you change that angle by even a degree however, the barrel should be fully qualified (indicated) prior to machining.
Hope this helps.
Here's how ours come out. This is right off the lathe with no polishing or fluff/buffin. All of ours are done with a single point tool-meaning a single cutter with a very sharp edge is used and the angle (11*) is machined with the tool doing the movement. Piloted cutters have multiple flutes and form the end into the final shape/angle. These can be used with success, but it's generally not the preferred method when building a rifle focused on shooting really well. As the photos show, a target style crown is fully exposed wheres a hunter/field crown is recessed into the barrel muzzle a little bit. This is for guns that see use in a vehicle. It keeps the muzzle out of the floorboards away from crud. The radial pattern in the last photo represents a clean exit. Everything is symmetrical which is really all your after. It's not voodoo or the product of divine power. Just good application of fundamental machine work.
C.
In a modern high performance centerfire cartridge, chamber pressures peak out as much as 60,000 CUP (Copper Units of Pressure)
How this translates into regular PSI I have no idea, but suffice to say it's a chitload that'll melt your face off if you don't build the gun right.
Ok, so several tons of "steam" behind the bullet. The projectile is accelerated from a dead stop to 2+ times the speed of sound in less than a meter of travel. In addition it's accelerated from a dead stop to upwards of 300,000 RPM in the same distance.
Lots going on there with powerful forces at play.
When we transition from supported motion to free flight it takes place at the muzzle. We want a clean transition with no influence on the bullet as it begins to fly. A proper crown (and there can be some variation on exactly how it ends up looking) will provide a clean/radial dispersion of the gas charge while at the same time offering zero influence on the bullet.
If the crown is cut "cockeyed" for instance, (meaning if you were to do something really foolish and cut it at 20* angle with a hacksaw) the gas on the trailing edge would meet the atmosphere before the opposite side. This would influence the exit and potentially ruin/degrade the accuracy.
A concentric edge free of machine/tool marks promotes better accuracy. The exact relief angle can be fiddled with to a certain point with basically no change.
Years ago (1950's) the US Army conducted a study on this subject. It was found that 11*'s offers the best accuracy. It's since become a cardinal rule of sorts. That being said there's a great many guns with 90* crowns that will get scarey small on paper. 90* crowns are far less work to machine because they don't require any real setup. Just stick it in the lathe and go. 90* is square regardless of how much the bore is jump roping around.
The second you change that angle by even a degree however, the barrel should be fully qualified (indicated) prior to machining.
Hope this helps.
Here's how ours come out. This is right off the lathe with no polishing or fluff/buffin. All of ours are done with a single point tool-meaning a single cutter with a very sharp edge is used and the angle (11*) is machined with the tool doing the movement. Piloted cutters have multiple flutes and form the end into the final shape/angle. These can be used with success, but it's generally not the preferred method when building a rifle focused on shooting really well. As the photos show, a target style crown is fully exposed wheres a hunter/field crown is recessed into the barrel muzzle a little bit. This is for guns that see use in a vehicle. It keeps the muzzle out of the floorboards away from crud. The radial pattern in the last photo represents a clean exit. Everything is symmetrical which is really all your after. It's not voodoo or the product of divine power. Just good application of fundamental machine work.
C.
Re: Want to learn about crowns...
Basically, if that portion of the crown that last touches the bullet upon exiting is concentric and perpendicular to the bore all is good. It doesn't matter if the crown is an 11 degree, USMC 45 degree pull back style, 90 degree, 15 degree, target, floor board or recessed or what ever you call it, it's all eye candy past the last touch point.
Basically, if that portion of the crown that last touches the bullet upon exiting is concentric and perpendicular to the bore all is good. It doesn't matter if the crown is an 11 degree, USMC 45 degree pull back style, 90 degree, 15 degree, target, floor board or recessed or what ever you call it, it's all eye candy past the last touch point.
Re: Want to learn about crowns...
Dixon that's what I was looking for... Thank you
Funny how a little help can turn on a little light upstairs and make perfect sense. The need for a proper crown seems obvious now. Although I'll have to do some more reading on variations of the crowns.
Dixon that's what I was looking for... Thank you
Funny how a little help can turn on a little light upstairs and make perfect sense. The need for a proper crown seems obvious now. Although I'll have to do some more reading on variations of the crowns.
Re: Want to learn about crowns...
I prefer a recessed 11 degree target. If its cut back .200 into the muzzle it makes it harder to damage in the field.
I prefer a recessed 11 degree target. If its cut back .200 into the muzzle it makes it harder to damage in the field.
Re: Want to learn about crowns...
i have a kidd rimfire barrel that has that same type of symetry.
pretty cool
explenation there Chad.
Ch
i have a kidd rimfire barrel that has that same type of symetry.
pretty cool
explenation there Chad.
Ch
Re: Want to learn about crowns...
William nailed it!!!! As did a couple of others.
I've always said the style of crown has no real bearing on accuracy. Weather it's a 11 degree, flat, stepped recessed, a sporter radius style etc...
What's key is to leave a crisp clean edge at the bore. No burrs etc...
I've seen barrels where you couldn't see any damage with the naked eye but you could see it with a bore scope.
I had a police offers gun a while back with our barrel on it. Gun had only 100+ rounds on it. It averaged 1" - 1.25" groups at a hundred yards. One land and one groove had a nick/ding to the edge.
I took the barrel off and recrowned it. Took it back to the range. First group with a cold clean barrel went into a 1/4" and the next 5 shot group went into 3/8" with box ammo.
Sent the gun back to him and was he happy!
I don't know who installed the barrel for him if the crown was done improperly at the time of installation of if he damaged it from cleaning.
Later, Frank
Bartlein Barrels
William nailed it!!!! As did a couple of others.
I've always said the style of crown has no real bearing on accuracy. Weather it's a 11 degree, flat, stepped recessed, a sporter radius style etc...
What's key is to leave a crisp clean edge at the bore. No burrs etc...
I've seen barrels where you couldn't see any damage with the naked eye but you could see it with a bore scope.
I had a police offers gun a while back with our barrel on it. Gun had only 100+ rounds on it. It averaged 1" - 1.25" groups at a hundred yards. One land and one groove had a nick/ding to the edge.
I took the barrel off and recrowned it. Took it back to the range. First group with a cold clean barrel went into a 1/4" and the next 5 shot group went into 3/8" with box ammo.
Sent the gun back to him and was he happy!
I don't know who installed the barrel for him if the crown was done improperly at the time of installation of if he damaged it from cleaning.
Later, Frank
Bartlein Barrels
Re: Want to learn about crowns...
I have a flat crown recessed on my 308 and 6.5 Creedmoor.
Bartlein just recrowned my 6XC when they recontoured it and I believe its the USMC style crown. It shoot lights out, as do the others.
The symmetrical carbon/finish wear pictured above is a must, and a very quick way to see anything obviously wrong.
I have a flat crown recessed on my 308 and 6.5 Creedmoor.
Bartlein just recrowned my 6XC when they recontoured it and I believe its the USMC style crown. It shoot lights out, as do the others.
The symmetrical carbon/finish wear pictured above is a must, and a very quick way to see anything obviously wrong.
Re: Want to learn about crowns...
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: wnroscoe</div><div class="ubbcode-body">Basically, if that portion of the crown that last touches the bullet upon exiting is concentric and perpendicular to the bore all is good. It doesn't matter if the crown is an 11 degree, USMC 45 degree pull back style, 90 degree, 15 degree, target, floor board or recessed or what ever you call it, it's all eye candy past the last touch point. </div></div>
Priceless! Well put
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: wnroscoe</div><div class="ubbcode-body">Basically, if that portion of the crown that last touches the bullet upon exiting is concentric and perpendicular to the bore all is good. It doesn't matter if the crown is an 11 degree, USMC 45 degree pull back style, 90 degree, 15 degree, target, floor board or recessed or what ever you call it, it's all eye candy past the last touch point. </div></div>
Priceless! Well put
Re: Want to learn about crowns...
So with all this talk of crowns, how is it that this barrel still shoots as well, despite it's crown being completely destroyed??
http://www.precisionshooting.com/psm_2011_03_frame.html
Food for thought.....
So with all this talk of crowns, how is it that this barrel still shoots as well, despite it's crown being completely destroyed??
http://www.precisionshooting.com/psm_2011_03_frame.html
Food for thought.....
Re: Want to learn about crowns...
Prolly the same way Tammy Forester's Anschutz 54 International smallbore gun holds national records/silver medals with a barrel that jumps from 22 to 25 caliber right smack dab in the middle.
Makes no sense whatsoever. It was the result of a squib load that she didn't catch till it was too late.
While there's no crystal ball for this stuff, the cardinal rules still apply; If you machine it well and its a quality part, chances are it'll work as advertised. If you go blacksmithing on it, sometimes you get lucky. Most times you don't.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Conclusion: Having a perfect
crown is an absolute requirement for
pinpoint accuracy...unless it isn’t.</div></div>
C.
Prolly the same way Tammy Forester's Anschutz 54 International smallbore gun holds national records/silver medals with a barrel that jumps from 22 to 25 caliber right smack dab in the middle.
Makes no sense whatsoever. It was the result of a squib load that she didn't catch till it was too late.
While there's no crystal ball for this stuff, the cardinal rules still apply; If you machine it well and its a quality part, chances are it'll work as advertised. If you go blacksmithing on it, sometimes you get lucky. Most times you don't.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Conclusion: Having a perfect
crown is an absolute requirement for
pinpoint accuracy...unless it isn’t.</div></div>
C.
Re: Want to learn about crowns...
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: C. Dixon</div><div class="ubbcode-body">If you machine it well and its a quality part, chances are it'll work as advertised. If you go blacksmithing on it, sometimes you get lucky. Most times you don't.</div></div>
Now that's a great way to put it! Usually absolutes only apply in internet discussions by those that repeat what they hear, but have no applicable experience.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: C. Dixon</div><div class="ubbcode-body">If you machine it well and its a quality part, chances are it'll work as advertised. If you go blacksmithing on it, sometimes you get lucky. Most times you don't.</div></div>
Now that's a great way to put it! Usually absolutes only apply in internet discussions by those that repeat what they hear, but have no applicable experience.
Re: Want to learn about crowns...
A few years ago a friend of mine had a barrel re crowned by a local ''tactical rifle expert''. This ''expert'' told my friend that the type of crown that he cut made the bullet more stable at ranges beyond 300 YDS. When my friend told me this i came real close to pissing my pants from LMFAO! My friend still believes what this guy told him.
A few years ago a friend of mine had a barrel re crowned by a local ''tactical rifle expert''. This ''expert'' told my friend that the type of crown that he cut made the bullet more stable at ranges beyond 300 YDS. When my friend told me this i came real close to pissing my pants from LMFAO! My friend still believes what this guy told him.
Re: Want to learn about crowns...
In reguards to burrs on the rifling in previous posts. Do you machine from the bore out when cutting the crown? I have always done mine that way but have seen videos online of people cutting from outside in. Does it make a diffrence?
In reguards to burrs on the rifling in previous posts. Do you machine from the bore out when cutting the crown? I have always done mine that way but have seen videos online of people cutting from outside in. Does it make a diffrence?
Re: Want to learn about crowns...
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: maccrazy2</div><div class="ubbcode-body">In reguards to burrs on the rifling in previous posts. Do you machine from the bore out when cutting the crown? I have always done mine that way but have seen videos online of people cutting from outside in. Does it make a diffrence? </div></div>
Yes, it most certainly does.
Couple reasons and I'll use an unrelated example to illustrate. just about anytime you use a tool that uses some kind of pressure to initiate a cutting action it creates a distortion/burr/load against the part its cutting.
If we buzz an endmill across a flat piece of steel it'll roll a burr at the very end. Why? At some point the remaining material cannot support itself against the pressure exerted by the tool.
In this sense the same action takes place while crowning. The tool (no matter how sharp) will roll an edge. By starting from the inside and working out towards the periphery the initial cut is well supported and will machine a very clean transition at the bore/crown intersection. This is what your really after. Beyond that point its all show, fluff, etc.
C.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: maccrazy2</div><div class="ubbcode-body">In reguards to burrs on the rifling in previous posts. Do you machine from the bore out when cutting the crown? I have always done mine that way but have seen videos online of people cutting from outside in. Does it make a diffrence? </div></div>
Yes, it most certainly does.
Couple reasons and I'll use an unrelated example to illustrate. just about anytime you use a tool that uses some kind of pressure to initiate a cutting action it creates a distortion/burr/load against the part its cutting.
If we buzz an endmill across a flat piece of steel it'll roll a burr at the very end. Why? At some point the remaining material cannot support itself against the pressure exerted by the tool.
In this sense the same action takes place while crowning. The tool (no matter how sharp) will roll an edge. By starting from the inside and working out towards the periphery the initial cut is well supported and will machine a very clean transition at the bore/crown intersection. This is what your really after. Beyond that point its all show, fluff, etc.
C.
Re: Want to learn about crowns...
Thanks Chad.
Thanks Chad.
