engineering question re: gun barrels

[Bulk Beef]

So there's an ongoing debate on the subject of fluting rifle barrels and whether it increases the rigidity of said barrel. I'm no ME, but my feeble mind says that fluting will save weight, allowing one to increase the OD of the barrel without incurring a weight penalty, thereby increasing rigidity. However, if one were to take a barrel of a given diameter (say 1") and simply flute the length, the rigidity would be reduced (compared to the 1" unfluted).

So the question is, does one of you engineering types actually have some math to either back up or refute my unscientific opinion?

 

[sygyzy]

I never heard this debate. I like fluting because of the weight savings while still maintaining the ID.

 

[Analog]

Originally posted by: sward666
So there's an ongoing debate on the subject of fluting rifle barrels and whether it increases the rigidity of said barrel. I'm no ME, but my feeble mind says that fluting will save weight, allowing one to increase the OD of the barrel without incurring a weight penalty, thereby increasing rigidity. However, if one were to take a barrel of a given diameter (say 1") and simply flute the length, the rigidity would be reduced (compared to the 1" unfluted).

So the question is, does one of you engineering types actually have some math to either back up or refute my unscientific opinion?

Fluting is not only used to save weight, but to increase heat dissipation. As a barrel heats up, accuracy is affected on subsequent shots. The problem with machining is that it also introduces stresses in the metal from local heating, so that the fluting itself may cause instablilities in the barrel and ruin accuracy.

 

[sygyzy]

Very good points!

 

[Walleye]

Originally posted by: yellowfiero

Originally posted by: sward666
So there's an ongoing debate on the subject of fluting rifle barrels and whether it increases the rigidity of said barrel. I'm no ME, but my feeble mind says that fluting will save weight, allowing one to increase the OD of the barrel without incurring a weight penalty, thereby increasing rigidity. However, if one were to take a barrel of a given diameter (say 1") and simply flute the length, the rigidity would be reduced (compared to the 1" unfluted).

So the question is, does one of you engineering types actually have some math to either back up or refute my unscientific opinion?

Fluting is not only used to save weight, but to increase heat dissipation. As a barrel heats up, accuracy is affected on subsequent shots. The problem with machining is that it also introduces stresses in the metal from local heating, so that the fluting itself may cause instablilities in the barrel and ruin accuracy.

actually, it's a cold barrel that's unpredictable, but if a barrel gets too hot, then it could do a few things.

if you're firing lead rounds, then it'll break apart the rounds while inside the barrel, and all that'll come out the end are a few fragments of lead. (thus, depositing lead w/in the barrel)

also, the heat could transfer to the chamber and start firing the rounds faster than you intended. this could be bad.

 

[Bulk Beef]

Originally posted by: yellowfiero

Originally posted by: sward666
So there's an ongoing debate on the subject of fluting rifle barrels and whether it increases the rigidity of said barrel. I'm no ME, but my feeble mind says that fluting will save weight, allowing one to increase the OD of the barrel without incurring a weight penalty, thereby increasing rigidity. However, if one were to take a barrel of a given diameter (say 1") and simply flute the length, the rigidity would be reduced (compared to the 1" unfluted).

So the question is, does one of you engineering types actually have some math to either back up or refute my unscientific opinion?

Fluting is not only used to save weight, but to increase heat dissipation. As a barrel heats up, accuracy is affected on subsequent shots. The problem with machining is that it also introduces stresses in the metal from local heating, so that the fluting itself may cause instablilities in the barrel and ruin accuracy.

Yeah, I know all that (one reason why it's not a bad idea to do the rifling after the fluting) but this is specifically about fluting and rigidity. A lot of guys seem to think that taking barrel X and fluting it will make it more rigid. I just don't see how removing material is going to do that.

 

[Analog]

The latest trend in barrels, beside cryogenic treatment either during the manufacturing stages or as an aftermarket process, is fluting. There's really no controversy about fluting; it works. Fluting a barrel definitely lightens it, stiffens it and cools it faster because it exposes so much more surface area. Because a certain wall thickness must be maintained for safety reasons, however, a barrel must be of a heavier contour than normal and the flutes can only be so deep. Depending on the length, width and depth of the flutes, the trade-off in terms of weight come close to being a wash. The net result is a thicker barrel than normal, but one that weighs about the same as a thinner, non-fluted one. How-ever, you still have the advantages that flutes provide. While on the subject of flutes, E.R. Shaw, Inc., was granted a patent recently for helical flutes. Because the flutes spiral around the outside of the barrel, they are longer for any given barrel length, and therefore lighten it to a greater degree and expose more surface area than a straight-fluted barrel. For the time being, Shaw plans to offer their helical-fluted barrels only in a non-tapered configuration, but hope to perfect the process to include tapered sporter barrels as well.

Text

 

[Nyical]

Gimme a free floating heavy barrel, great accuracy.

 

[Bulk Beef]

Originally posted by: yellowfiero
The latest trend in barrels, beside cryogenic treatment either during the manufacturing stages or as an aftermarket process, is fluting. There's really no controversy about fluting; it works. Fluting a barrel definitely lightens it, stiffens it and cools it faster because it exposes so much more surface area. Because a certain wall thickness must be maintained for safety reasons, however, a barrel must be of a heavier contour than normal and the flutes can only be so deep. Depending on the length, width and depth of the flutes, the trade-off in terms of weight come close to being a wash. The net result is a thicker barrel than normal, but one that weighs about the same as a thinner, non-fluted one. How-ever, you still have the advantages that flutes provide. While on the subject of flutes, E.R. Shaw, Inc., was granted a patent recently for helical flutes. Because the flutes spiral around the outside of the barrel, they are longer for any given barrel length, and therefore lighten it to a greater degree and expose more surface area than a straight-fluted barrel. For the time being, Shaw plans to offer their helical-fluted barrels only in a non-tapered configuration, but hope to perfect the process to include tapered sporter barrels as well.

Text

See, that's why there's a debate. You can read that same thing on the website of just about every barrel manufacturer out there, but nobody backs it up with any math. However, a quick and dirty google yielded this.

Reason I asked here is b/c I'm guessing there are more mechanical engineers here than at the gun sites.

 

[ZeroNine8]

Anytime you have a non-smooth surface feature, especially square corners but also somewhat in tight radius corners, you have a stress concentration. Because of this and the weak spots where material has been removed, you have to make the barrel thicker overall so that it doesn't crack under the high pressure of firing a shot. This is why they said that they increased the barrel thickness and fluted it so that you ended up with a fluted barrel of similar weight. The advantage claimed was that it dissipated heat faster than the non-fluted variety.

To answer the original question:

Now if you have two identical solid barrels and flute one of them, the original non-fluted barrel will be stiffer, fluting doesn't 'add' stiffness. The claim that it increases stiffness is because you can have a larger, stiffer barrel that is fluted such that it remains stiffer than the smaller, unfluted barrel, yet the two are comparable in weight. Basically fluted barrels are stiffer per unit weight than non fluted. This is the same reason bridges have trusses instead of being solid, the trusses are almost as stiff/strong as the solid bridge yet weigh considerably less.