Barrel Choice

Talk with other Shiloh Sharps shooters.

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BFD
Posts: 2789
Joined: Mon Jan 21, 2008 7:36 pm

Re: Barrel Choice

Post by BFD »

Aviator wrote: Wed May 13, 2020 10:23 am
BFD wrote: Wed May 13, 2020 9:07 am Charlie. Its geometry that counts here. Not algebra.

I think Aviator may have forgotten some geometry and trigonometry.
Maybe.... Maybe not.... :wink:
Waiting to see your calculation for the length of the perimeters of 1) 1 inch diameter circle, 2) the cross section of an octagon 1 inch across the flats, and 3) the cross section of an octagon 1 inch across the points...
Review your geometry. SIN not TAN. You have the length of the hypotenuse of your 16 right triangles where you should be using the opposite leg. Also, if you just think through it physically, or draw it in cross section, you can see it quite easily.
gunlaker
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Joined: Tue Jun 23, 2009 6:16 pm

Re: Barrel Choice

Post by gunlaker »

In 3 dimensions a sphere uses the least surface area per unit enclosed mass. In two dimensions, like the cross section of a barrel, a circle has the smallest circumference to enclose a given area. Not just smaller than an octagonal cross section, but smaller than any possible configuration.

So, for a given mass, the circular cross section has the least surface area and will radiate heat the slowest.

Chris.
BFD
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Joined: Mon Jan 21, 2008 7:36 pm

Re: Barrel Choice

Post by BFD »

But Chris, neither volume or cross sectional area are constrained in any way.

I'm taking a break planting veggies with my wife. So I'm not keeping up.
Aviator
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Re: Barrel Choice

Post by Aviator »

BFD wrote: Wed May 13, 2020 11:16 am
Aviator wrote: Wed May 13, 2020 10:23 am
BFD wrote: Wed May 13, 2020 9:07 am Charlie. Its geometry that counts here. Not algebra.

I think Aviator may have forgotten some geometry and trigonometry.
Maybe.... Maybe not.... :wink:
Waiting to see your calculation for the length of the perimeters of 1) 1 inch diameter circle, 2) the cross section of an octagon 1 inch across the flats, and 3) the cross section of an octagon 1 inch across the points...
Review your geometry. SIN not TAN. You have the length of the hypotenuse of your 16 right triangles where you should be using the opposite leg. Also, if you just think through it physically, or draw it in cross section, you can see it quite easily.
OK, let's back the truck up.

For the case where you are calculating the perimeter of an octagon cross section where you know the dimension across the flats:
You know the included angle (22.5 degrees).
You know the adjacent side.
You want to know the opposite side.
Tangent is absolutely appropriate. The tangent of the included angle is the opposite side divided by the adjacent side.

For the case where you are calculating the perimeter of an octagon cross section where you know the dimension across the flats:
You know the included angle (22.5 degrees).
You know the hypotenuse.
You want to know the opposite side.
Sine is appropriate. The sine of the included angle is the opposite side divided by the hypotenuse.

I stand by my calculations.

Next time we meet in person I'll draw you a sketch. :wink:
Dennis Armistead
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Location: Payson Arizona
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Re: Barrel Choice

Post by Dennis Armistead »

The area of a circle is πr2 , where r is the radius of the circle. But r = P/(2π), where P is the perimeter of the circle. So the area of the circle is P2 /(4π).
The area of a square is s2 , where s is the side length. But s = P/4, so the area of a square is P2 /16. Since 1/(4π) > (1/16), the circle has more area than the square.
The area of an octagon is where s is the side length, but s = P/8. So the area of an octagon is

Since this is less than 1/(4π), the circle has more area than the octagon.

Hope this clears it up.
Dennis
Experience trumps intelligence every time.
Kurt
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Re: Barrel Choice

Post by Kurt »

charlie young wrote: Wed May 13, 2020 8:14 am Kurt, don't worry buddy, I'll back you up with any prognosis you want to throw into the mix...after all I did pass College Algebra in 1971!!!!!!!!!!
Thank you. Hey I don't know the difference either :lol:
But I said that this is going to be interesting. :lol:
The reason a dog has so many friends is because he wags his tail instead of his tongue.

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gunlaker
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Re: Barrel Choice

Post by gunlaker »

BFD wrote: Wed May 13, 2020 11:30 am But Chris, neither volume or cross sectional area are constrained in any way.

I'm taking a break planting veggies with my wife. So I'm not keeping up.
That is true :-). It's also why this same discussion comes back all the time :-).

Personally I pick full octagon barrels on my Sharps rifles. I just like the way they look, and they certainly extremely well. I do like a part octagon on my schuetzen rifles as they feel a little less muzzle heavy that way.

Chris.
Steve Sudbeck
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Joined: Fri Feb 09, 2007 8:18 am

Re: Barrel Choice

Post by Steve Sudbeck »

Wow people, what an education for a barrel choice question - this is certainly a “full service” forum. As far as the math, a round barrel of like outside diameter is going to have more surface area than an octagon barrel; simply put, to make an octagon barrel out of a round barrel of like diameter, you must remove an arced surface to create each flat surface thus removing incremental surface area for each flat created (you can visualize it if you think about it). I thank you all for the help.
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bpcr shooter
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Re: Barrel Choice

Post by bpcr shooter »

it all depends on if you "inscribe" or "circumscribe" the octagon. with one, your circle will be bigger, with the other the octagon will be. I would have to say that even if the circle was bigger that a octagon would cool better, as the points will radiate heat faster than the circle will, just like modern cooling fins. not sure but it makes sense in my head anyway
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SFogler
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Joined: Tue May 19, 2015 9:19 am

Re: Barrel Choice

Post by SFogler »

Sheesh - I'm glad I played like a hedge fund investor and got a 32" half octagon!
Jimhp02
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Joined: Sat Mar 14, 2020 5:09 pm
Location: South Carolina

Re: Barrel Choice

Post by Jimhp02 »

Have a 30” Shiloh Sharps with octagon barrel coming. I just like the look of an octagonal barrel. Thank goodness all your math is over my head! 😂
Great stuff guys!

JimP
Jimhp02
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Location: South Carolina

Re: Barrel Choice

Post by Jimhp02 »

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