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Anglingarchitect
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Posted: 3/2/2010 9:44:24 AM
If you had the same amount of material overall (greater dia) to compensate for the material lost in the flutes then the stiffness would actually be increased! Think flanges of a steel beam being further from the neutral axis! But material removal will result in less stiffness and more bending!
Captains1911
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Posted: 3/2/2010 10:22:13 AM
[Last Edit: 3/2/2010 10:23:40 AM by Captains1911]
Originally Posted By Anglingarchitect:
If you had the same amount of material overall (greater dia) to compensate for the material lost in the flutes then the stiffness would actually be increased! Think flanges of a steel beam being further from the neutral axis! But material removal will result in less stiffness and more bending!


You are absolutely correct, however in the case of fluted barrels you are not increasing the diameter, you are removing material from a section of fixed inside and outside diameters, thus decreasing it's Ixx and therefor it's stiffness (resistance to bending around the X-X axis).
4schitzangiggles
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Posted: 3/2/2010 11:07:27 AM
Taking some materiel away from a barrel does not always result in a less stiff barrel. It depends more on where and how the materiel is taken away. If you take the I beam example the I beam has the same strength as solid box beam of the same dimensions, but with a reduction of @ 50% in weight and materiel. The outside most point of the flutes (the top of the flute) is further away from the neutral plane than a smaller diameter light weight barrel so it will be more rigid in that case. Because it has the same distance from the neutral plane as the heavy barrels profile the stiffness should be the same, for the same reason as the I beam vs. the solid beam but with out the weight penalty.

Seems like something for "The Box of Truth" (you know, the guys that actually know WTF they are talking about when it come to debunking firearms myths unlike those tools from SF with a TV show...)
A government big enough to give you everything you want is big enough to take everything you have.
Thomas Jefferson
Captains1911
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Posted: 3/2/2010 11:37:17 AM
[Last Edit: 3/2/2010 11:46:50 AM by Captains1911]
Originally Posted By 4schitzangiggles:
Taking some materiel away from a barrel does not always result in a less stiff barrel. It depends more on where and how the materiel is taken away. If you take the I beam example the I beam has the same strength as solid box beam of the same dimensions, but with a reduction of @ 50% in weight and materiel. The outside most point of the flutes (the top of the flute) is further away from the neutral plane than a smaller diameter light weight barrel so it will be more rigid in that case. Because it has the same distance from the neutral plane as the heavy barrels profile the stiffness should be the same, for the same reason as the I beam vs. the solid beam but with out the weight penalty.

Seems like something for "The Box of Truth" (you know, the guys that actually know WTF they are talking about when it come to debunking firearms myths unlike those tools from SF with a TV show...)


Sorry, but you are wrong. The moment of inertia of a solid box is much greater than that of a beam of similar flange and depth dimensions. Take an HP12x84 for example, which has a depth of 12.3" and a flange width of 12.3", and an Ixx of 650 in^4. Now calculate the Ixx of a solid 12.3"x12.3" box and you'll find that it's 1907 in^4, almost 3 times that of the HP section. Compare the moment of inertia of a hollow pipe to that of a solid circle, and you will see a similar relationship.



Plinker1022
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Posted: 3/2/2010 12:24:36 PM
[Last Edit: 3/2/2010 12:25:33 PM by Plinker1022]
Circulars cross sections such as a tube....such as a barrel is already the most efficient cross section regarding bending. All of the area is located away from the axis of bending and its bending characteristics are the same regardless of what axis you choose. Please remember I said efficient, not strongest or best.....I don't think fluting is going to hurt bending that much one way or another. Considering the increased heat transfer away from your barrel, I think fluting is a great idea. I've sold guns that got hot too quick and stayed hot for too long. I think this thread started as HBAR vs. M4. Wow. I agree Captain, sometimes you gotta pull the physics out.
Plinker1022
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Posted: 3/2/2010 12:32:31 PM
[Last Edit: 3/2/2010 12:34:01 PM by Plinker1022]
I hate too continue on but the square beam theory...fact...etc...you have but although it may be correct its not efficient at all. You quote three times the bending moment but look at area. The square 12.3 x 12.3 = 151.29 in2.

The HP section you provided, 24.6 in2.

So basically six times the area was used to get three times the bending resistance.
Captains1911
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Posted: 3/2/2010 12:33:25 PM
[Last Edit: 3/2/2010 3:36:34 PM by Captains1911]
Originally Posted By Plinker1022:
Circulars cross sections such as a tube....such as a barrel is already the most efficient cross section regarding bending. All of the area is located away from the axis of bending and its bending characteristics are the same regardless of what axis you choose. Please remember I said efficient, not strongest or best.....I don't think fluting is going to hurt bending that much one way or another. Considering the increased heat transfer away from your barrel, I think fluting is a great idea. I've sold guns that got hot too quick and stayed hot for too long. I think this thread started as HBAR vs. M4. Wow. I agree Captain, sometimes you gotta pull the physics out.


And I agree with you 100%, the benefits of fluting out weigh the minor loss in in bending resistance. I was just correcting the others who were suggesting that there is no loss at all in bending resistance.
Plinker1022
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Posted: 3/2/2010 12:35:38 PM
[Last Edit: 3/2/2010 12:38:29 PM by Plinker1022]
Yep...anytime you take area away from a section's extremities, bending is compromised. Consider an I Beam. Now chop of the top flange. You decreased area by roughly a third but decreased the bending moment by almost half. The area is oriented away from the axis of bending for a reason. Captain, what do you do...I've never seen someone pull out the second moment of area on a gun forum before.
Captains1911
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Posted: 3/2/2010 12:37:35 PM
[Last Edit: 3/2/2010 12:40:16 PM by Captains1911]
Originally Posted By Plinker1022:
I hate too continue on but the square beam theory...fact...etc...you have but although it may be correct its not efficient at all. You quote three times the bending moment but look at area. The square 12.3 x 12.3 = 151.29 in2.

The HP section you provided, 24.6 in2.

So basically six times the area was used to get three times the bending resistance.


We weren't discussing area and amount of material, but stiffness. This all started when I corrected "Chromelined's" comment about fluting not reducing stiffness, that is all.

Quote:
"Fluted barrels are awesome..I dont like the look of fluting but with the scalopped grooves you get just as much barrel stiffness and actually more surface area than it would have had even as an HBAR so it cools like a lightweight barrel.So like an HBAR fluted barrels give the same benefits with less weight and quicker cooling."
Plinker1022
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Posted: 3/2/2010 12:40:00 PM
[Last Edit: 3/2/2010 12:41:44 PM by Plinker1022]
Originally Posted By Captains1911:
Originally Posted By Plinker1022:
I hate too continue on but the square beam theory...fact...etc...you have but although it may be correct its not efficient at all. You quote three times the bending moment but look at area. The square 12.3 x 12.3 = 151.29 in2.

The HP section you provided, 24.6 in2.

So basically six times the area was used to get three times the bending resistance.


We weren't discussing area and amount of material, but stiffness. This all started when I corrected "Chromelined's" comment about fluting not reducing stiffness, that is all.


I know. I understand. I just can't help but think with efficiency in mind. You know this economy has got everything thinking efficiency around here. What field you work in? I've never seen someone pull out the second moment of area on a gun forum before.

Anglingarchitect
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Posted: 3/2/2010 3:11:04 PM
Captains1911 must be an engineer or had training in it! I'm an Architect so we have these discussions with our Structural Engineer all the time about Structures~~~~ Barrels not so much but the physics is still the same.
fuzzy03cls
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Posted: 3/2/2010 3:11:10 PM
I recently bought a 16" carbine HBAR upper. It's going to be my abuse upper. Little cleaning & lots of rapid fire mag dumps.
Upon putting it on my lower I did notice the weight difference. It's not much but you do feel it. Adding an eotech & MBUS balanced it out a little.
Under the had guards is THICK. There's almost no space between it & the gas tube.
Captains1911
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Posted: 3/2/2010 3:33:45 PM
[Last Edit: 3/2/2010 3:34:07 PM by Captains1911]
Originally Posted By Anglingarchitect:
Captains1911 must be an engineer or had training in it! I'm an Architect so we have these discussions with our Structural Engineer all the time about Structures~~~~ Barrels not so much but the physics is still the same.


Fields_Overseer
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Posted: 3/2/2010 4:25:25 PM
Originally Posted By 1saxman:
Many don't like fluted barrels but seem to like the 'dimpled' ones. I like the flutes - there's no question they remove more weight and provide more surface area than dimpling. Dimpling to me is strictly a cosmetic effect. That mutt I made is the only AR I have shot that hit the center at 25 yds with the aperture on the center line of the index. That actually speaks not to my assembly but of the man who built the upper. Plus, like Olympic or not, the one thing they always did well was barrels, and this one is no exception.


dimpling, when done properly(knights) removes more weight, is more rigid, and offers more cooling than fluting. Its better in every aspect which is why they do it. I doubt knights does stuff soley for looks.
Plinker1022
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Posted: 3/2/2010 4:29:45 PM
[Last Edit: 3/2/2010 4:32:34 PM by Plinker1022]
Originally Posted By Captains1911:
Originally Posted By Anglingarchitect:
Captains1911 must be an engineer or had training in it! I'm an Architect so we have these discussions with our Structural Engineer all the time about Structures~~~~ Barrels not so much but the physics is still the same.




Yeah I jumped over from the private side to a public utility about 2 years ago so it's been a long time since I actually practiced...engineering that is....I shot off about 200 yesterday.
glazer1972
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Posted: 3/2/2010 5:05:25 PM
16" Midlength Govt. Profile 1:7" Chrome Lined.

or

20" Govt. Profile 1:7" Chrome Lined.

المسيحي, النصراني

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A.R.M.S. AAC H&K Blackthorne/Vulcan/Hesse/Joeken/arpartskits.com
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