Does a barrel have to be cut before recrowning?
Reason I'm asking, I'm not a big fan of the round dome crown and was wondering if what it would take to have a deep hunting crown put on a rifle that is already crowned with the round dome crown...
Just takes a lathe and a good operator and about 30 minutes to perfection.....
There seems to be some accuracy testing support for an 11 degree target crown (dished back 11 degrees, instead of flat). However, if you don't make a crown flat, like Savage does on many of its rifles, you have to be sure the crown is concentric with the bore. A flat crown is always concentric.
If using a lathe you need to be sure it is a 4 jaw and the gunsmith centers the barrel on a tight pilot in the bore. This takes more time than doing a quick 3 jaw which centers on the outside diameter of the barrel. The other option is to use a piloted cutter.
There are two reasons to cut a barrel before re-crowning, one is to shorten the barrel, the other is to remove any damage to the bore at the muzzle. If the bore is in good shape and you just want the smith to change the crown, than it's a matter of removing the barrel from the action, centering the bore in the lathe and cutting the desired shape of crown.
Quite simple to put a deeper crown into the barrel, as to 11 (79) degree crown or a 90 degree crown, that's up to you. I've cut them both way and haven't seen an accuracy benefit of either design. I've read the 90 deg crown is better for flat base bullets and the the 11 deg for boat tails, I dunno if that is true. I do know that a fresh perfectly concentric crown can improve the accuracy of a rifle.
Does anyone know how the belief in the 11 degree crown being the most accurate came to be? I have heard a few different stories and nothing jives. What is the real story?
Just marketing, no real reason huh? Guess I should not be suprised.
I recall that a test was done by cutting different angles on the same barrel, and testing each angle to see what the accuracy was. It turned out that 11 deg. produced the tightest groups. However, I can't find the link in my saved favorites. This one may be of interest though:
Target Crown The thing has kind of become self perpetuating, in that the common target crown cutting tool is 11 degrees.
I won't recrown a barrel,unless I'm prepared to reblue it as well. Cold Blue just doesn't cut it and can be extremely corrosive to your bore, if you weren't careful about the application.
As for the crowning, that article has lots of holes in it.
First, the best crown you'll end up with is the one that was least touched by human hands.
When you cut a 90Deg. recessed crown, you rely more so on the accuracy of the lathe operating within its most accurate methods, than if you add in the action of the compound as well. It can still turn out to be very accurate, so long as it is done on a lathe, but I wouldn't dream of the brownells mandrel rig for recrowning a 22, much less a hunting rifle.
Next, you can take a perfectly cut crown in either a 11deg. or a recessed 90 and ruin it by trying to chamfer like they depicted in that article, the burr on the end of the muzzle. That burr, when the crown job is done correctly, is almost non-existent and will be the first time the rifle is shot. If you go monkeying with it using some kind of countersink or ball deburrer, you're going to mess up an otherwise perfect crown, or at least take a very good chance of it.
I use nothing but a recessed 90, simply because I know that it has the best chance of any crown at being accurate and it protects the crown from damage down the road better than anything else going too. Mine are always cut in a 4 jaw chuck on a lathe, dialed into the bore within .0001" and cut from the inside out.
I never use emery cloth, steel wool or anything else to remove burrs or chamfer edges, simply because it is not precision enough and you run the risk of screwing the whole thing up for nothing.
As far as having to cut the barrel, prior to crowning, it isn't necessary. More often than not, only .020-.050" of the barrel at the most has been damaged and in need of repair. Unless you intend on shortening the barrel considerably, or there is apparent damage inside the bore that exceeds about an inch, I just part it off in the lathe and crown from there.
The whole process is normally about 15 minutes, minus the time in blueing.
This photo shows a soot pattern deposited on a target crown:
http://www.flickr.com/photos/wmode/3354075063/. The uniformity of the pattern is said to be indicative of a concentric crown that is necessary for accuracy.
As for the 11-degree crown angle, here�s one man�s account of old experiments that led to that number:
http://yarchive.net/gun/barrel/barrel_crowning.html. I�d like to see more documentation of those experiments.
The author also mentions that a recessed crown will protect the rifling at the muzzle opening from impact. Whether the recessed crown protects the rifling at the muzzle from a cleaning rod is another matter.
Can't say for sure how long the 11deg. phenom has been around, but that's the very first time I've ever heard of someone saying it started back in the late fifties or early sixties.
That post kind of looks like a random opinion, rather than something with some facts behind it.
I've been out out of the benchrest circle for a spell. Are they using the 11 or are they still using the standard recessed 90 deg. crown?