What's the consensus on carbon fiber barrels?

[georgeib]

That is just thoroughly false. There are lots of situations where removing material can increase rigidity and or strength by distributing localized strain, reducing vibration, lowering inertia, etc. I'm not in a position to say if traditional flutes do any of that to a barrel or not, but if the aforementioned engineer at Knight's really said that then he's probably right because it is hypothetically possible.

One example I can think of would be tapering a bull barrel. By tapering the barrel it has less mass at the end and that will reduce the stress applied during barrel whip without compromising stiffness. That material at the end of the barrel is essentially doing nothing, as all the strain is isolated more towards the middle. The reason they leave that material on a bull barrel is to resist thermal expansion at the crown.

Okie, would you care to give us a brief CV so we can take you a bit more seriously, please? You make general statements about, "lots of situations," but I think we'd like some enumeration of just a couple of those "situations."

Examples using math would be the most convincing. Thank you.

[lysander]

That is just thoroughly false. There are lots of situations where removing material can increase rigidity and or strength by distributing localized strain, reducing vibration, lowering inertia, etc. I'm not in a position to say if traditional flutes do any of that to a barrel or not, but if the aforementioned engineer at Knight's really said that then he's probably right because it is hypothetically possible.

One example I can think of would be tapering a bull barrel. By tapering the barrel it has less mass at the end and that will reduce the stress applied during barrel whip without compromising stiffness. That material at the end of the barrel is essentially doing nothing, as all the strain is isolated more towards the middle. The reason they leave that material on a bull barrel is to resist thermal expansion at the crown.

You fail mechanics of materials.

Stiffness is normally denoted as k

k = 3EI/L^3

with:

E = modulus of elasticity
L = length
I = second area moment of the cross-section

So, let us look at two barrels, the one a straight one inch in diameter, and the other tapered, starting at one inch and tapering to 0.500 inch at the muzzle. Both are the same caliber, overall length and made from the same material, so L and E will be the same, so the only thing than changes the stiffness is I

I for a round cross section with a round hole in its center (a thick walled tube) is:

(π/4) x [(R2^4) - (R1^4)]

with:

R1 = inside diameter (bore which is constant)
R2 = outside diameter

Since R2 on the straight sided barrel in constant, and R2 on the tapered barrel starts at 1 but decreases to 0.50. Therefore, I for the tapered barrel will always be less than I for the straight barrel, as will the stiffness.

[okie]

You fail mechanics of materials.

Stiffness is normally denoted as k

k = 3EI/L^3

with:

E = modulus of elasticity
L = length
I = second area moment of the cross-section

So, let us look at two barrels, the one a straight one inch in diameter, and the other tapered, starting at one inch and tapering to 0.500 inch at the muzzle. Both are the same caliber, overall length and made from the same material, so L and E will be the same, so the only thing than changes the stiffness is I

I for a round cross section with a round hole in its center (a thick walled tube) is:

(π/4) x [(R2^4) - (R1^4)]

with:

R1 = inside diameter (bore which is constant)
R2 = outside diameter

Since R2 on the straight sided barrel in constant, and R2 on the tapered barrel starts at 1 but decreases to 0.50. Therefore, I for the tapered barrel will always be less than I for the straight barrel, as will the stiffness.

But reducing stiffness in that area in this case is irrelevant. It might be relevant with a big heavy silencer or perhaps a bipod located at the very end of the barrel like on some MGs, but as far as a bare muzzle is concerned reducing the stiffness at the end of the barrel isn't going to result in greater deflection at the muzzle. And with the reduced inertia it should result in less, at least theoretically. Point is, a barrel with a slight taper isn't going to whip more, and might even whip measurably less.

[1168]

But reducing stiffness in that area in this case is irrelevant. It might be relevant with a big heavy silencer or perhaps a bipod located at the very end of the barrel like on some MGs, but as far as a bare muzzle is concerned reducing the stiffness at the end of the barrel isn't going to result in greater deflection at the muzzle. And with the reduced inertia it should result in less, at least theoretically. Point is, a barrel with a slight taper isn't going to whip more, and might even whip measurably less.

Read the room.

[MegademiC]

I've never heard the term heat bending before, but I think what they're talking about is dipping the barrel in liquid nitrogen to normalize it. It's very common if not universal in barrel manufacturing.

Normalizing is heat treatment where the steel is completely recrystalized and slowly brought down in temp to remove any stresses. It results in a full-soft temper.

I think you are referring to cryogenic treatments, which Im unfamiliar with.

[lysander]

But reducing stiffness in that area in this case is irrelevant. It might be relevant with a big heavy silencer or perhaps a bipod located at the very end of the barrel like on some MGs, but as far as a bare muzzle is concerned reducing the stiffness at the end of the barrel isn't going to result in greater deflection at the muzzle. And with the reduced inertia it should result in less, at least theoretically. Point is, a barrel with a slight taper isn't going to whip more, and might even whip measurably less.

First off, you said it was false that removing material always reduces stiffness. I showed that stiffness will always be reduced when material is removed, because the 2nd moment of cross section area is the moment of the area, and with a tube, if the area is smaller, the stiffness will be smaller.

The only way to increase stiffness of a tube is to increase the cross section area.

And, all of the barrel moves when it whips, so more overall stiffness is always better, even if only by a teeny, tiny amount.

[okie]

First off, you said it was false that removing material always reduces stiffness. I showed that stiffness will always be reduced when material is removed, because the 2nd moment of cross section area is the moment of the area, and with a tube, if the area is smaller, the stiffness will be smaller.

The only way to increase stiffness of a tube is to increase the cross section area.

And, all of the barrel moves when it whips, so more overall stiffness is always better, even if only by a teeny, tiny amount.

The strain is concentrated at or near the chamber, can we agree on that? I get that the stiffness is reduced at the point where the material is removed, but the strain is far, far less at the muzzle, and the deleted material will reduce strain at the base where it's most concentrated. Same reason a flag pole is tapered.

Therefore, the tapered barrel will not deflect more than a non tapered one. Not due to barrel whip, or even due to loading in the case of a non free floated barrel. Reducing stiffness at an area where there's less strain does not reduce the overall stiffness of the barrel with regard to how it's stressed. In other words, it effectively increases the stiffness of the barrel.

And yes I get that that's not the definition of stiffness but that's what people mean when they talk about the stiffness or rigidity of a barrel, which you obviously know good and well and are just here to harass me but whatever. Apparently I'm the resident whipping boy now so have at it.

[okie]

Normalizing is heat treatment where the steel is completely recrystalized and slowly brought down in temp to remove any stresses. It results in a full-soft temper.

I think you are referring to cryogenic treatments, which Im unfamiliar with.

Yes sir you're right that's what I meant but I couldn't remember what it was called.

[lysander]

The strain is concentrated at or near the chamber, can we agree on that? I get that the stiffness is reduced at the point where the material is removed, but the strain is far, far less at the muzzle, and the deleted material will reduce strain at the base where it's most concentrated. Same reason a flag pole is tapered.

Therefore, the tapered barrel will not deflect more than a non tapered one. Not due to barrel whip, or even due to loading in the case of a non free floated barrel. Reducing stiffness at an area where there's less strain does not reduce the overall stiffness of the barrel with regard to how it's stressed. In other words, it effectively increases the stiffness of the barrel.

And yes I get that that's not the definition of stiffness but that's what people mean when they talk about the stiffness or rigidity of a barrel, which you obviously know good and well and are just here to harass me but whatever. Apparently I'm the resident whipping boy now so have at it.

First "strain" is directly proportional to the amount of deformation experienced by an object under loading. Therefore, it is not concentrated at or near the chamber, but where the barrel sees the highest bending, say in between nodes?

So, you might want to rethink that last statement.

Short argument, people have been making bull barrels for low rate fire accuracy (e.g., bench rest shooting, where that rate of fire is low enough that barrel heating is not a major issue) for at least two centuries, and they work very well in that regard.

[MegademiC]

The strain is concentrated at or near the chamber, can we agree on that? I get that the stiffness is reduced at the point where the material is removed, but the strain is far, far less at the muzzle, and the deleted material will reduce strain at the base where it's most concentrated. Same reason a flag pole is tapered.

Therefore, the tapered barrel will not deflect more than a non tapered one. Not due to barrel whip, or even due to loading in the case of a non free floated barrel. Reducing stiffness at an area where there's less strain does not reduce the overall stiffness of the barrel with regard to how it's stressed. In other words, it effectively increases the stiffness of the barrel.

And yes I get that that's not the definition of stiffness but that's what people mean when they talk about the stiffness or rigidity of a barrel, which you obviously know good and well and are just here to harass me but whatever. Apparently I'm the resident whipping boy now so have at it.

Less mass, given the same impulse, will move more, faster.

And your original claim was that removing material can make an object more rigid. With a tapered barrel, area of flex that has the most impact is at the base, thats why preference is to have thicker material there... its more rigid/stiff.

Flag poles are tapered for reasons related to wind harmonics and not related to the discussion at hand.