Gunsmithing How important is the Crown?

[JWG]

I had always thought the crown MUST BE PERFECT or accuracy will be shit. Then one day I bought a 1940's .22 LR bolt gun. It was stunningly accurate at 50 yards. Not match-worthy, but notably, the bore was pitted, and the rifling itself looked like the yellow-lines on a road that we see jokes about drunks creating. Looked like some bad "chatter" in the button or tooling. Not surprising given what was happening in America in the 40's and how the priority was for a .22 bolt gun...

Anyway, I did more digging, and found this article: http://www.longrangehunting.com/articles/rifle-crown-1.php

SO...is that article "legit"? Is the crown really that incidental?

 

[kortik]

I had always thought the crown MUST BE PERFECT or accuracy will be shit. Then one day I bought a 1940's .22 LR bolt gun. It was stunningly accurate at 50 yards. Not match-worthy, but notably, the bore was pitted, and the rifling itself looked like the yellow-lines on a road that we see jokes about drunks creating. Looked like some bad "chatter" in the button or tooling. Not surprising given what was happening in America in the 40's and how the priority was for a .22 bolt gun...

Anyway, I did more digging, and found this article: http://www.longrangehunting.com/arti...le-crown-1.php

SO...is that article "legit"? Is the crown really that incidental?

This article did not say anything about the distance to the target. If you shoot at exactly the same distance all the time, and if crown is uneven and not concentric, group size may still be good and it is possible to adjust sights to match POA and POI at some very specific distance.This is because even if bullet is given some extra "push" to the side on its exit from the barrel, which may "complicate" bullet trajectory, using exactly the same distance to the target will likely result in some sort of consistency. However, if distance to the target is changed, bullet, due to it's "complicated", by uneven and non concentric muzzle crown, trajectory, may end up going God knows where, even if vintage is appropriately adjusted to match the distance. This is what the author of this article did not try, and this is why he is so much confused about importance of the "perfect" crown.

Having concentric and uniform muzzle crown for shooting at various distances with predictable sights adjustments is very important.

 

[JWG]

It states that the target is at 100 yards. If the sights can be adjusted to hit at 100, for windage, it is the same as at 1000. Angular deviation is angular. Damage to the projectile should theoretically result in erratic or large groups, as the bullet rotates of course, and the damaged surface would not always present to one orientation.

 

[diverdon]

I don't believe that that a rifle with a bad crown will be accurate.

 

[kortik]

It states that the target is at 100 yards. If the sights can be adjusted to hit at 100, for windage, it is the same as at 1000. Angular deviation is angular. Damage to the projectile should theoretically result in erratic or large groups, as the bullet rotates of course, and the damaged surface would not always present to one orientation.

If bullet is pushed by uneven gas distribution, due to the damaged crown, on bullet exit from the barrel, trajectory will not be simply angular. It will be both spiral and angular. Angular factor can be adjusted by elevation, but spiral factor influence on POI is really difficult to predict at various distances. It is a bit simplistic representation, but with uneven crown, bullet trajectory become a lot more complicated than just a vertical bullet drop at various distances.

Note: I should have used "elevation" instead of "vintage" in my original reply. Sorry about making this typo.

 

[JWG]

If bullet is pushed by uneven gas distribution, due to the damaged crown, on bullet exit from the barrel, trajectory will not be simply angular. It will be both spiral and angular. Angular factor can be adjusted by elevation, but spiral factor influence on POI is really difficult to predict at various distances. It is a bit simplistic representation, but with uneven crown, bullet trajectory become a lot more complicated than just a vertical bullet drop at various distances.

Note: I should have used "elevation" instead of "vintage" in my original reply. Sorry about making this typo.

I honestly am un-sure, but wouldn't fleet-yaw be radically increased leading to unpredictable radial dispersion, and in EXTREME events, reduced GSTAB which results in a tumble? it seems even the buggering this guy did didn't cause that though.

 

[...]

.22s are strange......and they do things you wouldnt expect......its honestly like they have a mind of their own.....you really cant use performance of a .22 as a barometer of centerfire performance.


but i will say, i recrowned a bad muzzle on my .308.......and that caused my group to go from 1.5 MOA to .9 MOA........

 

[Pakratt99]

If you take 20 identical rifles, 10 with perfect crowns and the other 10 with crown issues the perfect lot as a group will always outshoot the issue group. When you isolate it to a 1v1 ratio if you say took the worst shooting perfect crown in comparison to the best crown issue rifle you might find its not a major issue. Correlation doesn't always equal causation but in the BR world, crown care and maintenance is about their top priority for good reason.

 

[JWG]

How did the rifle in the article shoot FAR BETTER with a totally jacked up crown than without? It is a SINGLE VARIABLE situation. Same gun, same ammo...different crown. Why?

 

[Pakratt99]

Link to the article isn't working for me, but I'm assuming its not a single variable situation. If you took two identical models of rifle but one has a bad crown and the other a perfect one you can still have other variables in play. This is the reason you hear some people say they have a "good" or "bad" barrel when its identical to their previous one.

 

[CharlieNC]

Maybe, it all depends.

 

[STI_1911_Guy]

The crown being the last thing that touches the bullet before it leaves or as it leaves SHOULD have some effect on the accuracy undoubtedly, and a jacked up crown shouldn't shoot as well as a clean one if compared identically (impossible) the clean crown will average a better outcome guaranteed. However the absolute perfection needed of a crown may be exaggerated.............kinda like seating depth...........

 

[Shanerbanner10]

Here's another thing to throw into this conversation. Some smiths will not leave a barrel without an 11 degree crown, some cut a flat crown and some prefer a recessed flat or 11 degree crown. Which is correct and why? Does one shoot better than the other?

My opinion as a shooter is that it doesn't not matter. Even if the crown is uneven the bullet should still react the same way as long as the cuts do not have excessive burs and such that would harm the integrity of the bullet itself. I could definitely be wrong but logic says if that problem products consistent results (which I'm thinking an uneven crown would produce consistent results one way or another) then the problem can be adjusted for in the zero process and again when doping the rifle. I could definitely be wrong here...

 

[kortik]

https://en.wikipedia.org/wiki/Internal_ballistics

"The purpose of the barrel is to provide a consistent seal, allowing the bullet to accelerate to a consistent velocity. It must also impart the right spin, and release the bullet consistently, perfectly concentric to the bore. The residual pressure in the bore must be released symmetrically, so that no side of the bullet receives any more or less push than the rest. The muzzle of the barrel is the most critical part, since that is the part that controls the release of the bullet.

......

The muzzle of the barrel is the last thing to touch the bullet before it goes into ballistic flight, and as such has the greatest potential to disrupt the bullet's flight. The muzzle must allow the gas to escape the barrel symmetrically; any asymmetry will cause an uneven pressure on the base of the bullet, which will disrupt its flight. The muzzle end of the barrel is called the "crown", and it is usually either beveled or recessed to protect it from bumps or scratches that might affect accuracy. A sign of a good crown will be a symmetric, star-shaped pattern on the muzzle end of the barrel, formed by soot deposited, as the powder gases escape the barrel. If the star is uneven, then it is a sign of an uneven crown, and an inaccurate barrel."

 

[samson7x]

Has anyone noticed a measurable degradation in accuracy as carbon builds up on the crown associated with suppressor use?

 

[Eagle1899]

Has anyone noticed a measurable degradation in accuracy as carbon builds up on the crown associated with suppressor use?

Nope, I've done back to back before and after with no difference.

 

[FrankieJames7]

i am going to have to say no. bryan litz talks a little about how a bullet flies and it is basically that a gun "throws" a bullet, and if the bullet is spinning fast enough the oncoming air will straighten it if it is slightly tumbling or crooked. in practical long gun shooting, the trick for precision groups is to consistently "throw" the bullet the same way before the air pressure stabilizes the bullet(bryan calls it "putting the bullet to sleep"). if the bullet leaves the barrel the exact same way each time it is going to group good if it is flying crooked or pushed off to the side by uneven gas pressure

 

[skeetlee]

Not that i would ever suggest this! I have a 300 yard range right behind my rifle shop. Concrete benches, wind flags, the hole works. Benchrest quality range. I build rifles in my shop for lots of people with great success. With that said, i have done some pretty silly things, just to see what happens. I took a know well shooting 6ppc barrel one afternoon and ched it up in a 3 jaw chuck and faced off the crown. No dialing in!! None!! The dam thing shot lights out. I thin chucked the same barrel back up, and cut an 11 degree crown. Again, nothing dialed in. 3 jaw chuck. the barrel still shot lights out. I then dialed the barrel in properly and cut a faced off crown. I shot another group. all three groups looked the same and they all measure 3 shots in the 1's at 100 yards. Hmm I thought to myself. I haven't re tested this little experiment, as it takes no time to cut a crown properly. Not to mention the peace of mind. I was however really surprised at what i found. take this for what its worth.. NOt Much!! LOL Lee

 

[Fursniper]

https://en.wikipedia.org/wiki/Internal_ballistics

"The purpose of the barrel is to provide a consistent seal, allowing the bullet to accelerate to a consistent velocity. It must also impart the right spin, and release the bullet consistently, perfectly concentric to the bore. The residual pressure in the bore must be released symmetrically, so that no side of the bullet receives any more or less push than the rest. The muzzle of the barrel is the most critical part, since that is the part that controls the release of the bullet.

......

The muzzle of the barrel is the last thing to touch the bullet before it goes into ballistic flight, and as such has the greatest potential to disrupt the bullet's flight. The muzzle must allow the gas to escape the barrel symmetrically; any asymmetry will cause an uneven pressure on the base of the bullet, which will disrupt its flight. The muzzle end of the barrel is called the "crown", and it is usually either beveled or recessed to protect it from bumps or scratches that might affect accuracy. A sign of a good crown will be a symmetric, star-shaped pattern on the muzzle end of the barrel, formed by soot deposited, as the powder gases escape the barrel. If the star is uneven, then it is a sign of an uneven crown, and an inaccurate barrel."

Finally, someone who got it right.......

 

[FrankieJames7]

Not that i would ever suggest this! I have a 300 yard range right behind my rifle shop. Concrete benches, wind flags, the hole works. Benchrest quality range. I build rifles in my shop for lots of people with great success. With that said, i have done some pretty silly things, just to see what happens. I took a know well shooting 6ppc barrel one afternoon and ched it up in a 3 jaw chuck and faced off the crown. No dialing in!! None!! The dam thing shot lights out. I thin chucked the same barrel back up, and cut an 11 degree crown. Again, nothing dialed in. 3 jaw chuck. the barrel still shot lights out. I then dialed the barrel in properly and cut a faced off crown. I shot another group. all three groups looked the same and they all measure 3 shots in the 1's at 100 yards. Hmm I thought to myself. I haven't re tested this little experiment, as it takes no time to cut a crown properly. Not to mention the peace of mind. I was however really surprised at what i found. take this for what its worth.. NOt Much!! LOL Lee

if you are kind enough, shoot groups at 1 2 and 3 hundred yards with a perfect 11 degree crown, then fuq it up with a nail or knife and repeat. see if the groups have any unpredicted change in trajectory, particularly laterally