crown recessed muzzle how does it help?

Any shape crown is meant to protect the end of the rifling against hard knocks.

The present shiny cone is a styling feature.
 
Yep, it keeps the edge tucked out the way so it can't get marred or nicked, as that would cause the rounds to get jerked out of balance when they passed over the roughed up spot.
 
Agree with the above posts. There is an actual crown which is the small surface where the end of the lands & grooves are polished to ensure that it is concentric to the bore. Then there is the decorative crown which could be a raised part to protect the actual crown. Some long range guns have an eleven degree crown that to the eye, appears to be a slight dish. Why eleven? From studying photographs of the bullet as it exits the bore, it was determined that the gases travel outward at eleven degrees.
 
I have already recessed the muzzle with a reamer .100 bigger than the bore 1/4 to 1/2 inch with no ill effect. Anyway, I could not see a difference.
 
We may be talking about different things. If the bullet exit point is not perfect, one side of the base of the bullet can exit before the other side. The gas will exit on the one side first, tipping the bullet as it leaves the muzzle and resulting in inaccuracy. The bullet exit point is not the "crown". The crown is a higher point intended to protect the exit point from damage.

Now if the barrel behind the exit point is damaged in some way, possibly one side is worn due to use of a cleaning rod, the gas escape will be uneven. The exit point can look good but the rifle will not be accurate. One way to restore some better accuracy is to counter bore the barrel back far enough to cut away the defective part of the barrel; that creates a new exit point behind the muzzle. Doing that will never restore the rifle to the accuracy it had, in part because the gas escaping around the bullet in that half inch or so will disrupt its flight, but it will be better than having the bullet tip at the exit point.

Jim
 
Many 'smiths call the flat or rounded surface at the muzzle end's outside diameter in the "face" and the few thousandths inch out from the bore across the rifling the crown. The crown was made smooth to remove any burrs that would engrave the bullet on its exit. A few folks did accuracy tests with barrels faced to different angles and found an 11 degree face was best. The crown could be most any angle and had no appreciable effect, but most were made with a brass crowning ball charged with a fine abrasive.

Jim K.:
Now if the barrel behind the exit point is damaged in some way, possibly one side is worn due to use of a cleaning rod, the gas escape will be uneven. The exit point can look good but the rifle will not be accurate.
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All the 7.62 NATO Garand barrels I wore out had no copper wash for the last 2/3 to 3/4 inch of the bore at about 5000 rounds when accuracy got noticably reduced. They all shot under 1 MOA at 600 at the time but started out better. The solid steel cleaning rod used did its thing lapping away the bore and groove surfaces. But the "belled" muzzle was the same for every shot fired between cleanings. All those M1's used by fellow team members had no copper wash the last several fractions of an inch of the bore depending on the number of rounds fired. And there was always more wear on one side opposite the other side of the bore.

One way to restore some better accuracy is to counter bore the barrel back far enough to cut away the defective part of the barrel; that creates a new exit point behind the muzzle. Doing that will never restore the rifle to the accuracy it had, in part because the gas escaping around the bullet in that half inch or so will disrupt its flight, but it will be better than having the bullet tip at the exit point.
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Several 'smiths catering to the US Olympic Team's smallbore shooters have counterbored muzzles back an inch or more to get rid of the irregular dimensions at the barrel's muzzle. Accuracy was improved by that recessed muzzle.

Competitive shooters have been using "bloop tubes" to extend their front sight for decades. Both rimfire and centerfire have those aluminum tubes about 3/4" inside diameter that clock in place for repeatable zeros with the sights. They're from a couple to over a foot long clamped onto the barrel's muzzle. No degradation of accuracy whatsoever.

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It has been my (very limited) experience that conterboring restores some accuracy lost due to the worn barrel, but you seem to be saying that counterboring will make the accuracy as good or better than it was when the barrel was new. If that is true, why would not barrel makers counterbore their new barrels?

I believe a 3/4 inch tube is large enough that gas disturbance is not a problem,

Jim
 
Jim:
. . .you seem to be saying that counterboring will make the accuracy as good or better than it was when the barrel was new.
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I didn't say that nor was it implied. I did say counterbored muzzles did fix barrels with poor rifling quality at the muzzle. If the last inch or so of the barrel is good, counterboring does nothing for accuracy.

Button, cut and broach rifled barrels have dimensional problems at both ends for an inch or so. That's caused by the tool not being well supported by the blank's bore diameter as it makes the grooves. Chambering the back end gets rid of that bad area at the breech and cutting off, or counterboring the muzzle end fixes that part. New, good quality barrels don't need counterbored, but some smiths do that to double protect the muzzle crown.

I believe a 3/4 inch tube is large enough that gas disturbance is not a problem
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Do you think a slotted tube on the muzzle with about 1/16th inch or less clearance to the bullet would cause accuracy problems with an otherwise very accurate barrel?
 
It did not cross my mind when I first read this, but shotguns are an excellent example. I have worked on shotguns that people wanted to use with slugs and the muzzle was not at 90* with the bore. That usually really screws up the accuracy. It is a good example of projectile "Tip off".
 
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