crown? whats its secrets?

[mozeppa]

i read a lot about this and that ....what what exactly is a " barrel crown"?

how does it affect bullet strike?

how is it done wrong?...right?

as i see it... once the bullet leaves the barrel ...what does the end of the barrel have to do with the way its cut?

[dilly]

Have you ever thrown a good shot in basketball, but a defender barely nicked it with his finger as it left your hand so it flew way off? That's what having a damaged crown can do. If the bullet can't leave the muzzle without interference, it can't fly straight. I think that's about as scientific as I know how to get with it.

[country gent]

The crown is the transition from the bore to the muzzle. Lands and grooves are configured with a sharp smmoth surface that is square and true to provide a true even release of the bullet from the bore. Any burrs, dings, cleaning rod wear, or even a poorly cut finished crown can distort the bullets base and cause an uneven release of the bullet. A quick look when shooting cast lubed bullets at the lube star on the muzzle shows the tale. an uneven start or lopsided is an indicator of a poor crown. An quick easy way to re cut a crown is to use a brass ball and lapping compound to polish the edge into true form again. On rifles that need to be cleaned from the muzzle this damage can occur from the rod also. If you use the same ball everytime it dosnt take long to touch up a crown. A brass round head screw does a great job also. Some fine lapping compound on the head. work in a figure 8 pattern with light pressure holding the head into the bore work until no dings grooves or rough areas show under magnification.

[pietro]

i read a lot about this and that ....what what exactly is a " barrel crown" ? - country gent is correct.

how does it affect bullet strike ? - Even w/o burrs, if the edge of the rifling @ the muzzle isn't square to the bore, gas will escape past the base of the bullet on one side, deflecting the boolit to one side and contribute to boolit wobble (not condusive to good accuracy).

how is it done wrong ?... In ways too numerable to list here - refer to "Bubba gunsmithing".

right ? - I've long (45 years) used country gent's method, successfully.

as i see it... once the bullet leaves the barrel ...what does the end of the barrel have to do with the way its cut?




I hope we've answered your questions. . :drinks:


.

[gnoahhh]

One of the more scientifically oriented gentlemen in the CBA recently did a series of tests with purposely damaged crowns and published his results in The Fouling Shot. He started with a rifle and load of known accuracy and then started inflicting damage to the crown including having at it with a coarse rasp and ended up by driving a lag bolt in. The results were surprising and laid to rest a lot of myths concerning crowns. In all instances point of impact shifted, sometimes dramatically, but also sometimes accuracy (group size) actually improved- but never suffered. The lesson I took from that is don't sweat the configuration of a crown, and if a defect is present don't panic until accuracy is disproved. Care merely need be taken during a hunting trip or during a match when re-zeroing isn't an option if one damages one's crown midway through.

[B R Shooter]

First, I agree that a crown should be even, consistent all around the barrel/bore. I think the actual crown makes little difference, flat, 11 degree, recessed, it's what is at the bore that makes the difference.

Personally, I do not agree with the brass ball, or any method of lapping, for one reason. The actual use and application of that means the pressure is pushing back into the bore. Any crown should be cut in a lathe and the tool should be pulled out and away from the bore. At least it should be cut perpendicular. If a non-lathe method has to be used, then a piloted center drill or even the reamer can freshen and true the crown. The qualifier here is the use of a pilot bushing that fits the BORE properly, which aligns the cutting tool.

I know many lap crowns and have for decades, but I don't.

[Blackwater]

There are a lot of theories about crowns, and people always do what they believe in, of course. Why not? For my own purposes, I love theory and theories, but I tend to look at results to guide my actions. Beliefs are fine, but experience is pretty much final for me. I can't explain it definitively, but my experience has indicated that the main thing is that the crown - which is the edge where the muzzle releases the bullet from the barrel - be very burr free and clean and smooth. If the bullet leaves the barrel cleanly, smoothly and easily, then it kind'a stands to reason that it'd shoot straight, but that's just theory, of course, and the results of polishing the crown as I outlined in another thread has proven to significantly improve accuracy in a number of rifles I've tried it on, and have seen others try it on. That later is the definitive part for me. I'm not totally content with not knowing or fully understanding WHY it works, but I'm very happy that it DOES.

[randyrat]

I cut a barrel off with a Hack saw once and only once...I was so embarrassed at the results, too embarrassed to bring it to a real gunsmith. So I spend 2 weeks off and on working to square it up and create a good crown so it would shoot as good as it did before, many times walking away frustrated grinding my teeth..
I finally got it and learned a good lesson. Never again.
Very little will throw your shot off with a bad crown.

[Huffmanite]

I've re-done crowns on a number of older rifles with decent success using a Lee Case Trimmer. Guys at Surplus Rifle forum.com made a sticky about it in their gunsmithing forum.

http://www.surplusrifleforum.com/viewtopic.php?f=79&t=63966

[Ballistics in Scotland]

It just means that the muzzle has to part company with the bullet at exactly the same moment on all sides. A perfectly flat muzzle, making sharp 90 degree edges with all the grooves and lands, would work perfectly. The reason we don't rely on that is that a slight accidental knock would produce burrs on one or two of the lands, and not on the others. So we have to recess the muzzle slightly to guard against this.

I once rebarrelled a rifle with a Shilen barrel, and testfired it with the 60 degree beveled muzzle which Shilen used for turning it down to contour on a lathe. The lathe centre had produced tiny burrs on every land, and yet the rifle delivered excellent accuracy, because the muzzle was burred identically all round.

A really bad crown may set the bullet wobbling, and produce serious and unpredictable inaccuracy. Lesser defects move the point of impact, but may still give good groups. When a double rifle delivered pair-of-spectacles groups from the two barrels, surprisingly slight beveling of the muzzles was an easier way of putting it right than shiftng the soldered packing pieces and relaying the ribs.

I don't like the often recommended screw and grinding paste methods. Brass wears as well as steel, and you can easily end up with a groove cut into the brass, and a lop-sided, tapered bore right at the muzzle. If you must do it, you should use a hand-cranked drill, and keep moving the handle in a circle around where an extension of the bore would be. A lathe and crowning tool with a caliber-specific pilot is a counsel of perfection, which may not suit an amateur who will do this job only once. My own preference is to put a ball-shaped tungsten carbide burr in the vice, and rotate the barrel against it. The only way I can imagine this getting lop-sided would be if the barrel came with an action which was much heavier on one side than the other.

[Petrol & Powder]

It just means that the muzzle has to part company with the bullet at exactly the same moment on all sides. A perfectly flat muzzle, making sharp 90 degree edges with all the grooves and lands, would work perfectly. The reason we don't rely on that is that a slight accidental knock would produce burrs on one or two of the lands, and not on the others. So we have to recess the muzzle slightly to guard against this.

I once rebarrelled a rifle with a Shilen barrel, and testfired it with the 60 degree beveled muzzle which Shilen used for turning it down to contour on a lathe. The lathe centre had produced tiny burrs on every land, and yet the rifle delivered excellent accuracy, because the muzzle was burred identically all round.

A really bad crown may set the bullet wobbling, and produce serious and unpredictable inaccuracy. Lesser defects move the point of impact, but may still give good groups. When a double rifle delivered pair-of-spectacles groups from the two barrels, surprisingly slight beveling of the muzzles was an easier way of putting it right than shiftng the soldered packing pieces and relaying the ribs.

I don't like the often recommended screw and grinding paste methods. Brass wears as well as steel, and you can easily end up with a groove cut into the brass, and a lop-sided, tapered bore right at the muzzle. If you must do it, you should use a hand-cranked drill, and keep moving the handle in a circle around where an extension of the bore would be. A lathe and crowning tool with a caliber-specific pilot is a counsel of perfection, which may not suit an amateur who will do this job only once. My own preference is to put a ball-shaped tungsten carbide burr in the vice, and rotate the barrel against it. The only way I can imagine this getting lop-sided would be if the barrel came with an action which was much heavier on one side than the other.

/\ THIS IS THE BEST POST ON THIS TOPIC /\

Ballistics in Scotland, you nailed it!

[johnson1942]

my crowns are perfect and look like chrome when i do them. take you gun out at the darkest night if you live very rural. have someone fire it safely as you stand back on the side of it. the fire ball at the muzzle should have no fingers coming off of it. the fire ball should be shaped in such a way one side looks like another, no differences at all in the area around it. if their is your not getting the groups you should with you gun. ive seen nicks in the crown that made the bullet pushed in a direction that wasnt correctable with the sights. a new crown changed that. i use the crowning kit i got from brownells with alot of extra pilots i also bought from them years ago. i have three crowning tools. 90 degree, 45 degree and 79 and 1/2 degree. i usually use the 45 degree. but have used the 79 and 1/2 on some guns. usually takes me about 1/2 hour to crown a muzzle like chrome and perfectly and i use no power tool but my hands and arms. a perfect crown is one of many spokes in the wheel of makeing a rifle shoot to it max.

[StolzerandSons]

When a double rifle delivered pair-of-spectacles groups from the two barrels, surprisingly slight beveling of the muzzles was an easier way of putting it right than shiftng the soldered packing pieces and relaying the ribs.

This is horrible advice on regulating double rifles. I build double rifles for a living and if I ever did that my customers would send the rifle back as they should. This might move the bullets point of impact but I guarantee that at anything other than at a specific distance the bullets will eventually start to keyhole.

If you would like a good example of how bad an idea this is, just google Sabatti double rifles and Cabelas. They made the mistake of trying to regulate/re-regulate the lazy and cheap way by filing the muzzles. It pretty much ruined the Sabatti name in the double rifle market in the U.S.

There is a reason double rifles are expensive, it's because they require a lot of hand labor to build properly.

[M-Tecs]

When I first started building long range match rifles I did everything with 11 degree crown. Latter I started comparing the 11 degree to a recessed target crown. I mostly use the recessed target crown now. This is based on my own testing and tests that I have read but well done they are all basically equal. Dents will move POI but have surprisingly little effect on accuracy. Cleaning rod wear can affect accuracy greatly.

Some intersting reading on effect of crowns

https://www.youtube.com/watch?v=gsg-Yt6t-HM

http://www.accuratereloading.com/crownr.html

http://www.accuratereloading.com/223crn.html

http://www.longrangehunting.com/articles/rifle-crown-1.php

http://benchrest.com/showthread.php?75671-Barrel-Crown

http://bulletin.accurateshooter.com/?s=crown+damage&submit=Search

http://www.accurateshooter.com/technical-articles/barrel-cleaning-debate/ some talk of cleaing and crowns

http://forums.nitroexpress.com/showflat.php?Cat=0&Number=183746&page=0&fpart=all&vc=1

[Char-Gar]

There is no real secret to a barrel crown. When the bullet exists the muzzle the hot gases that pushed it out come out also. These gases need a uniform base to push against or the bullet will be shoved one way or another. Lots of folks argue about what a crown should look like, but anything that is uniform and even all around works just fine.

[dtknowles]

One of the more scientifically oriented gentlemen in the CBA recently did a series of tests with purposely damaged crowns and published his results in The Fouling Shot. He started with a rifle and load of known accuracy and then started inflicting damage to the crown including having at it with a coarse rasp and ended up by driving a lag bolt in. The results were surprising and laid to rest a lot of myths concerning crowns. In all instances point of impact shifted, sometimes dramatically, but also sometimes accuracy (group size) actually improved- but never suffered. The lesson I took from that is don't sweat the configuration of a crown, and if a defect is present don't panic until accuracy is disproved. Care merely need be taken during a hunting trip or during a match when re-zeroing isn't an option if one damages one's crown midway through.

What was the level of accuracy, we talking about sub MOA with a purposely damaged crown?

Tim

[Ballistics in Scotland]

This is horrible advice on regulating double rifles. I build double rifles for a living and if I ever did that my customers would send the rifle back as they should. This might move the bullets point of impact but I guarantee that at anything other than at a specific distance the bullets will eventually start to keyhole.

If you would like a good example of how bad an idea this is, just google Sabatti double rifles and Cabelas. They made the mistake of trying to regulate/re-regulate the lazy and cheap way by filing the muzzles. It pretty much ruined the Sabatti name in the double rifle market in the U.S.

There is a reason double rifles are expensive, it's because they require a lot of hand labor to build properly.

It wasn't advice. It is a makeshift which a gunsmith or dealer shouldn't do, and serves Cabelas right, though probably not Sabatti. Just like an irregular crown in a single rifle, anything more than a slight bevel is likely to cause wobbling, and I can't see why there would be a specific distance at which it wouldn't. But a slight bevel may work.

[wv109323]

In a rifle the operating pressure is usually between 30,000 to 70,000 psi. The instant the bullet leaves the barrel that pressure has to go somewhere. If that pressure is relieved unevenly around the base of the bullet(as in a bad crown) it will upset the bullet. Think of a bullet with an angled base to the bore. When that bullet exits the muzzle it will be upset due to gas escaping to one side of the angled base.
This also applies to cast boolits. If the base of the bollit is not flat and consistent then you get the same effect as a bad crown. The base of a cast boolit is the most critical part.

[M-Tecs]

The pressure at the muzzle is much less than max chamber pressures. The M1 Garand specs for gas port pressure are 6,000±2,000 p.s.i. http://m1-garand-rifle.com/garand-troubleshooting.php


Slower powders will have higher muzzle pressures. Crooked bases will open up groups. Crooked crowns effect point of impact but tend not to change group size. I have tested jacketed bullets before and after fixing crowns. I have not tested plain base lead so they may be effected more by crooked crowns.

[DougGuy]

In a rifle the operating pressure is usually between 30,000 to 70,000 psi. The instant the bullet leaves the barrel that pressure has to go somewhere. If that pressure is relieved unevenly around the base of the bullet(as in a bad crown) it will upset the bullet. Think of a bullet with an angled base to the bore. When that bullet exits the muzzle it will be upset due to gas escaping to one side of the angled base.
This also applies to cast boolits. If the base of the bollit is not flat and consistent then you get the same effect as a bad crown. The base of a cast boolit is the most critical part.

+1

If the base of the boolit is not square/perpendicular to the bore, gas will escape on one side prematurely and begin to push against the boolit which for another nanosecond or so is still engaged with the bore because that side of the boolit is longer, and it will allow the boolit to be pushed away from a straight line of flight and it will then take an angled flight path. Same with a crown that isn't concentric and square with the bore. It lets gas vent on one side while the other side is still sealed by the boolit.

I choose to cut pistol crowns on a 20° angle for one so an 11° crown can be cleaned up without shortening the barrel, and also because when you look at that fireball leaving the muzzle, it looks like 20° ~ 22° is parallel with the sides of the fireball. If the gas pressure departed the barrel in a 90° angle I would want to cut crowns at 90° but burning gases don't exit at 90° (180° included angle) they are closer to 70° measured center of the bore to the outer edges of the fireball, which would be 140° included angle if you add both sides. Subtract this from 180° and divide the remaining 40° by 2 because you have two sides of the angle, and it leaves 20° this is how I arrived at the angle which I use to crown barrels.

[Rifle 57]

Here is one of my crown jobs148660

[Ballistics in Scotland]

That would be just as good a crown as any, even if the bottom of the recess is at right angles to the bore. There are no real secrets of the crown. It just has to be, like the schoolboy definition of a circle, something that is round, all round.

One exception is that a crown shouldn't be too gradual a V shape. The gas is springy, and if you compress and release the weak little spring from your ballpoint pen, it goes into orbit. Also bathwater of a temperature you can just bear to immerse yourself in, because it builds up a boundary layer cooled by your 98.4 degree body, can be very painful as it flows straight from the faucet. If the gas can escape at the edges while the bullet base is blocking most of its escape route, it accelerates to great speed, and erodes the muzzle a little further back.

It is worth mentioning for some that an 11 degree crown means 11 degrees from perpendicular to the bore axis.

[Rifle 57]

That would be just as good a crown as any, even if the bottom of the recess is at right angles to the bore. There are no real secrets of the crown. It just has to be, like the schoolboy definition of a circle, something that is round, all round.

One exception is that a crown shouldn't be too gradual a V shape. The gas is springy, and if you compress and release the weak little spring from your ballpoint pen, it goes into orbit. Also bathwater of a temperature you can just bear to immerse yourself in, because it builds up a boundary layer cooled by your 98.4 degree body, can be very painful as it flows straight from the faucet. If the gas can escape at the edges while the bullet base is blocking most of its escape route, it accelerates to great speed, and erodes the muzzle a little further back.

It is worth mentioning for some that an 11 degree crown means 11 degrees from perpendicular to the bore axis.

Ballistics you are 100% correct I have tried every crown- angle - recess - flat - that you can think of using a barrel blocked rail gun and it makes no difference as long as the exit is a perfect 90 degrees to the bore.

Loren

[Tackleberry41]

I see some saying a bad crown may affect point of impact but not group size. One of my mosins, it shot pretty good, jacketed or cast as I bought it, just lucky I guess. I cut it back a little messing with the lathe, could still crown it in the lathe, still shot good. Cut the barrel back to a point where it would not go thru the headstock to be able to crown it. I tried a tool I had, it looked decent enough. But it went from good groups to all over the place, 8" groups at 50yds. Was going to give up on the rifle, thinking maybe it got cut back to a wide spot in the barrel. Its a questionably made wartime production rifle, alot of wobble when in the lathe. Midway finally had the PTG crowning tool in stock, vs what Brownells wants. Those groups are back to nickel sized at 50yds. It did not take much to mess things up.