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TheRealJobe

Nova Barrel defect?

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Forgive me I am new to the world of firearms and this may be a basic question.... I recently purchased a Nova, upon cleaning it I looked through the barrel from the stock end, and roughly 4 inches in from where I was looking I see a ring about a 1/2 inch thick. Unlike the rest of the barrel the ring is not reflective and upon skewing my viewing angle it almost appears as though the ring is made by something being placed in the barrel and spun around the inside scratching it. However, its such a clean and even ring I would have to imaging it occurred during manufacturing. I've tried to place a pencil in the barrel to see if I could feel any scratching, but I cant. Is this a defect, or should the ring be there? What purpose does it serve?

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As Banjo said, it is the forcing cone.

 

What is a forcing cone, you ask?

 

The forcing cone is where the inside diameter of the barrel transitions from the chamber diameter, which for a 12 gauge barrel is about 0.800 inches, to the bore diameter, which for a 12 gauge barrel is about 0.729 inches (nominally, unless your gun is back-bored in which case it'll be slightly bigger.)

 

This cone starts approximately at the end of the chamber (so for a gun with a 3" chamber, the cone would start at about 3 inches from the breech end of the barrel.)

 

This is also why you should never use longer shells than what your gun is made for. If, for example, you put a 3 inch shell in a chamber made for 2-3/4 inch shells only, it will still fit, but as you fire the gun and the shell's crimp opens, the forcing cone doesn't allow it to get all the way open, which can cause high pressures in the chamber, which the gun is not made for.

 

Why does your barrel have this change in diameter from the chamber to the barrel?

 

The chamber has to be a large enough diameter to accept the shell, which is substantially larger in diameter than the wad/shot cup, which is what comes out of the shell and heads on down the barrel and out the muzzle when the gun is fired.

 

The forcing cone is somewhat of a carry-over from the days of paper or cardboard wads, when a very tight seal was needed to minimize blow-by of the gases from the burning powder. Modern wads do a much better job of sealing the barrel than the old cardboard wads did.

 

If your barrel were the chamber diameter (0.800 inches) for its full length, it would still work, and probably just fine, since modern wads are soft plastic and are "cupped" at the end, and will spread out or "obturate" to seal even a very large diameter barrel.

 

But most manufacturers still make barrels with the old nominal 0.729 diameter, which is why most barrels will have a forcing cone.

 

Good question.

Edited by timb99

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As Banjo said, it is the forcing cone.

 

What is a forcing cone, you ask?

 

The forcing cone is where the inside diameter of the barrel transitions from the chamber diameter, which for a 12 gauge barrel is about 0.800 inches, to the bore diameter, which for a 12 gauge barrel is about 0.729 inches (nominally, unless your gun is back-bored in which case it'll be slightly bigger.)

 

This cone starts approximately at the end of the chamber (so for a gun with a 3" chamber, the cone would start at about 3 inches from the breech end of the barrel.)

 

This is also why you should never use longer shells than what your gun is made for. If, for example, you put a 3 inch shell in a chamber made for 2-3/4 inch shells only, it will still fit, but as you fire the gun and the shell's crimp opens, the forcing cone doesn't allow it to get all the way open, which can cause high pressures in the chamber, which the gun is not made for.

 

Why does your barrel have this change in diameter from the chamber to the barrel?

 

The chamber has to be a large enough diameter to accept the shell, which is substantially larger in diameter than the wad/shot cup, which is what comes out of the shell and heads on down the barrel and out the muzzle when the gun is fired.

 

The forcing cone is somewhat of a carry-over from the days of paper or cardboard wads, when a very tight seal was needed to minimize blow-by of the gases from the burning powder. Modern wads do a much better job of sealing the barrel than the old cardboard wads did.

 

If your barrel were the chamber diameter (0.800 inches) for its full length, it would still work, and probably just fine, since modern wads are soft plastic and are "cupped" at the end, and will spread out or "obturate" to seal even a very large diameter barrel.

 

But most manufacturers still make barrels with the old nominal 0.729 diameter, which is why most barrels will have a forcing cone.

 

Good question.

Great reply. I asked this previously and did not get good answers. I thought no one really know what it was. But now I know.

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