Gunsmithing Crowning a barrel
- Thread starter MachoMan
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Either will work as long as you're getting a clean cut and not leaving a bur in the muzzle. The sharp corner may give better accuracy, but is also at somewhat higher risk to damage than the more obtuse angle of a chamfer.
I like the piloted 60 deg cutters and cut deep enough to get the groove too.
I make the (11*) cut and then hold a piece of scotchbrite on it for a second to polish it and break any microscopic burrs.
Works great. If you are concerened about crown damage, you need to be more careful how you treat your rifle.
Works great. If you are concerened about crown damage, you need to be more careful how you treat your rifle.
11 degree facing operation from center out. Check for burrs with a Q-Tip.
Any chamfer will cause gasses to escape unevenly. The lands will disengage first, with a jet of gas from each one. Then the grooves will disengage with a high pressure release all the way around the bullet. This will upset just about any bullet to some degree, because most bullets are not perfect. A boat tail will suffer from this more than a flat base bullet.
Crown a barrel with 11* and shoot several groups. Now cut a chamfer and shoot a few groups. With the same ammo, the groups with the chamfer will be bigger. Not always by a lot, but it's there.
just my 2 cents...
Crown a barrel with 11* and shoot several groups. Now cut a chamfer and shoot a few groups. With the same ammo, the groups with the chamfer will be bigger. Not always by a lot, but it's there.
just my 2 cents...
I don't think it would make a difference (chamfer vs non-chamfer) given that the lands are grooves are equally spaced radially. It's when gas is released on one side before the other that the pressure imbalance would affect the attitude of the bullet.
Dial your muzzle in by the bore and single point cut the crown with an 11 degree face and a 60 degree chamfer at the lands. I leave sharp 90 degree crowns on BR rifles but not field rifles.
In a perfect world the chamfer would be fine. It's the imperfect bullets that cause the uneven gas release.
If the chamfer causes an issue, isn’t an 11 deg crown producing the very same issue but to a lesser degree? By your logic all crowns should be 90 deg, no?
A much lesser degree, yes. But it's many times easier to keep an 11* crown centered and straight than a 45-60* chamfer. As the angle increases, the error multiplies exponentially. a flat crown would be ideal for accuracy, but offers no protection. The 11* crown offers some protection while being flat enough to minimize error.
it'shard enough to make "perfect" bullets where the boat tail is perfectly concentric and even or where the flat base is perfect.
Any error in the bullet can add to the error at the crown and cause problems.
You could always recess the flat crown to protect it. I’ve never been able to demonstrate one angle works better than another. Unlike most BR rifles, we’re shooting through a multitude of different muzzle devices generally. So many opportunities for gas to surpass the bullet and affect it. As long as the crown is bore concentric, i’m happy.
As @Praeger said. I usually do rebated "hunting" crown, with 11deg internal. Use cotton tip (q-tip) after to draw it in and out and see if any whispy bits get stuck on a burr. If it doesn't snag or catch, you are good to go. By request I have put a 45deg chamfer ONLY on the rifling, so they are cut, but the actual bore is not cut.
I generally use an 11 degree or a flat crown. About the only reason I can see for a chamfer is to make sure the barrel is being spun concentric to the bore.
In my opinion, behind a muzzle device the secondary crown no longer serves any purpose. You might as well go with whatever single angle crown you like best, and hope for the best as the bullet passes through the brake/can. If it's exposed then it can offer a degree of protection.
As far as best shape or angle, there are a lot of ways to crown that all work well. Look at the deep V and convex spherical crowns the Russians used to use on some of their small bore target rifles. Like it was said above, as long as it's concentric it's probably going to work.
As far as best shape or angle, there are a lot of ways to crown that all work well. Look at the deep V and convex spherical crowns the Russians used to use on some of their small bore target rifles. Like it was said above, as long as it's concentric it's probably going to work.
Are you suggesting there is another way than cutting a thread concentric to the bore ? Dialling to the bore is the only way to ensure everything aligns properly.
If the bullets are imperfect, then
Why would any change in an angle be more prone to error exponentially? Error radially, or axially? Why is a flat crown ideal for accuracy? The purpose of cutting an angled crown is to provide some recess to protect the bore/groove to muzzle face junction. That's it. 11 degrees isn't a magical number, just a commonly used (and probably often eyeballed) setting. I think there is far too much attributed to the crown than is warranted.
I wouldnt chamfer. If there is a burr at the end of the rifling the first bullet you fire will remove the bur. I specifically asked this same question to a well respected gunsmith; this was the answer given.
My apologies if I misunderstood your question.
My apologies if I misunderstood your question.
You may be right.
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The only kind of rifles I own are hunting rifles and I don't like 11° crowns. I like 30° crowns with a very narrow 60° chamfer at the bore and a rim about .060" wide on the OD of the barrel. The depth of the 30° angle and rim width will vary depending on the muzzle diameter but I like to end up with about a .100" deep recess from the muzzle face to the lands.
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I experimented like this a few years ago, as many have. I read an article about how crowns "don't mean as much as you think" etc.
For "average shooters", it's not overly important. As long as it passes the cotton test, it will work. 11deg, 30deg, rebated, just a basic chamfer, etc. They work. This is why most of these tech articles can "prove it's not important".
When you start doing this commercially, as a 'smith and for customers, you VERY quickly have people who can out shoot you, by a good margin.
It matters to them. They can tell the difference between primer brands, how the brass was prepared, types of triggers that are all set to 1lb pull weight, etc.
Most people are not consistent enough to shoot 0.20" 5 shot groups on demand, on multiple rifles (that are capable).
Treat your customers with respect, and imagine that they CAN shoot those groups, and the crown starts to matter.
As @Supersubes and @MachoMan have shown, it's not hard to produce a great quality crown, so why would you settle for less ?
For "average shooters", it's not overly important. As long as it passes the cotton test, it will work. 11deg, 30deg, rebated, just a basic chamfer, etc. They work. This is why most of these tech articles can "prove it's not important".
When you start doing this commercially, as a 'smith and for customers, you VERY quickly have people who can out shoot you, by a good margin.
It matters to them. They can tell the difference between primer brands, how the brass was prepared, types of triggers that are all set to 1lb pull weight, etc.
Most people are not consistent enough to shoot 0.20" 5 shot groups on demand, on multiple rifles (that are capable).
Treat your customers with respect, and imagine that they CAN shoot those groups, and the crown starts to matter.
As @Supersubes and @MachoMan have shown, it's not hard to produce a great quality crown, so why would you settle for less ?
I don't think anyone is suggesting the crown isn't important. It's about putting it into perspective. Like so many aspects of machining a barrel, understand the choice you make, understand how to perform the operation, and if you are performing work for someone else, be prepared to answer their questions correctly.
If they are a 0.20" 5 shot group shooter, you give them what they ask for. For everyone else, you give them your best advise (to include, "Leave the crown alone - it's fine.") and let them chose.
I think we're all in agreement. Recently there have been so many "Just Got a Borescope - I Think My Barrel is Junk" threads and didn't want to leave any reader of this thread with the impression that one crown is better than another, or just because they can't get a barrel to get below .75 MOA that they need a new crown.
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I feel that there is actually more importance in the crown being cut consistent than the chamber being zero run out. The barrel ( having a good barrel ) and the actual bedding are the most important items to accuracy of the rifle The high dollar action is also just a bling item. Sure all the components straight and square add up to a very nice dependable rifle. And when my customer gets my rifle if has everything as close as possible. But a lot of it is over kill. I see some chambers that would make you cry and still shoot very well. I was told long ago by a hall of fame bench rest shooter and builder all this don’t mean nothing but you better always do it right and clean this is so they all can’t talk about you when the take your gun apart. A little off subject But a good crown in any shape is important and only the true shooters will ever tell the difference
Just a thought ?
Just a thought ?
We agree on a few things, but I'll disagree, respectfully, on this.
Importance of presentation or "what you can see", then yes. In terms of importance for accuracy, no.
I have physically tested a zero run out chamber I personally cut VS a "close enough is good enough" chamber I cut. I'll let you guess which worked better. One side effect I found was reloading. It artificially warped brass, to the point you could measure run out (out of the chamber on shot brass) on a concentricity gauge. A correctly dialled chamber, the brass came out the way it went in, perfect. (Die quality and brand also made a difference I found).
I've seen how other 'smiths around here do work (or what they have shown). If they are paying this much attention to a crown, I'd expect their chambers, threads, surface squareness to also be on point.
Wow, we drifted off topic a bit. Sorry for that.
Yes. I hope i didn’t come across as it is ok to have a run out chamber and yes i strive for zero as we all should hence why i have a $3000.00 chuck on my lathe. I see other smiths work very often and the attention to detail seems to be gone in some. I haven’t never tried to run a bad chamber to study it’s effects but I’ve seen chambers up to .005 from other smiths that shot lights out on the bench In my mind it always come down the where the bullet starts and the barrel.
No, not at all. Here's a good way to look at it. Formula 1 race cars. You have 5 (I think ?) Manufacturers on the line, all with different philosophical approaches, and vastly different engineering approaches. The cars lap within a few tenths of each other on a 1min+ lap time. That's incredible.
If you want to comment "oh yeah, but Mercedes is clearly better because they are winning, etc..." If you put Vettel or Hamilton in other cars, they would be at the pointy end, they are hired guns.
Not everyone can exploit all the power and ability of the car. If you put me in Hamilton's F1 car,I'd be so slow I wouldn't quality.
The same happens for rifles. You have different 'smiths approaching an end result in different ways. Only the top end shooter can exploit what the Smith produces. This is why some shooters go to different 'smiths to find one that "vibes" with them. Same with F1 drivers who change teams and do better / worse..
It's not that one Smith is awesome, one is crap. It's finding a balance of what works for you. 90deg vs 60deg action, 2 stage vs single stage trigger. OEM manufs can't please everyone, and neither can a 'smith.
If you want to comment "oh yeah, but Mercedes is clearly better because they are winning, etc..." If you put Vettel or Hamilton in other cars, they would be at the pointy end, they are hired guns.
Not everyone can exploit all the power and ability of the car. If you put me in Hamilton's F1 car,I'd be so slow I wouldn't quality.
The same happens for rifles. You have different 'smiths approaching an end result in different ways. Only the top end shooter can exploit what the Smith produces. This is why some shooters go to different 'smiths to find one that "vibes" with them. Same with F1 drivers who change teams and do better / worse..
It's not that one Smith is awesome, one is crap. It's finding a balance of what works for you. 90deg vs 60deg action, 2 stage vs single stage trigger. OEM manufs can't please everyone, and neither can a 'smith.
that is exactly how I do it too. after trying multiple angles, 11 seems to be the best for me.
at the early stage of my 'tinkering' I used a brass crown jig with a fine lapping compound on it to eliminate micro burrs...
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