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What is the purpose or the crowning at the end of a rifle barrel and how can it b done if a barrel is shortened?
Crowning??????
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The most important part of the rifling is the very end because its the last rifling a bullet passes over.The first 20 inches dont count if the muzzle has a problem.A crown protects the end from dents to some degree,and creats a smooth final surface for the bullet.If you simply hack saw the last couple inches off, the muzzle has a uneven surface with nicks that you cant see,but the bullet will find on the way out destroying your accuracy.You can get as fancy as buying a hand crowning tool from brownells for about 70 bucks,or as simple as putting a round headed brass screw covered with valve lapping compound in a power drill. After you have filed the new muzzle flat place the screw in the bore,and turn it on.Move the drill in a circle.Check after a minute.It will cut the metal back in a bevel.your done.
The barrel will be just as accurate, for a while, if you just file it completely flat and smooth, at right angles to the bore axis. All that matters is that gases don't exit on one side before the other, and the muzzle doesn't scrape a bit of metal off one side. Either of these will cause the bullet to wobble in flight.
The reason muzzles aren't flat, is that a trifling knock can burr over one or two of the lands. I use a ball-shaped tungsten carbide burr of about 1in. diameter (it could be down to 1/2in. for a small bore.) But I don't use it in the drill, for it can easily wander to one side, and so can the screw and grinding paste, if you accidentally apply sideways pressure. The Brownells tool has a pilot rod to fit the bore, and keep it aligned.
What I do is to hold the burr in a vice, or a hole in a doorframe etc. I then rotate the barrel against it, equalising the cutting effect around the edge of the bore. About 1/32in. deep gives all the protection you need.
The reason muzzles aren't flat, is that a trifling knock can burr over one or two of the lands. I use a ball-shaped tungsten carbide burr of about 1in. diameter (it could be down to 1/2in. for a small bore.) But I don't use it in the drill, for it can easily wander to one side, and so can the screw and grinding paste, if you accidentally apply sideways pressure. The Brownells tool has a pilot rod to fit the bore, and keep it aligned.
What I do is to hold the burr in a vice, or a hole in a doorframe etc. I then rotate the barrel against it, equalising the cutting effect around the edge of the bore. About 1/32in. deep gives all the protection you need.
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Target crowns are often dead flat, except for a little ridge a bit back from the bore to protect the edge of the bore and crown. Another popular non-rounded crown is a shallow beveled crown sloping into the bore, 11 degrees being popular.
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