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SSShooter
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Inscribed Octagon Dimensions
Sep 29th, 2016 at 6:56am
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Have my new barrel and have done the math on making the 1.200" round section (5" at the breech end) full octagon to make it similar to the original Hepburn Creedmoor rifles. Any of you math wizards want to post the width of the octagon section dimension to double-check my work before I put this on the mill and start removing metal. I'll be 'internet challenged for the next several days, but will post my math next week to compare (don't want to influence anyone's work ahead of time).
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Glenn
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old7groove
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Re: Inscribed Octagon Dimensions
Reply #1 - Sep 29th, 2016 at 7:19am
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To determine octagon dimension across flats - divide 1.200 by 1.08 = 1.111.
7~
  
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nuclearcricket
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Re: Inscribed Octagon Dimensions
Reply #2 - Sep 29th, 2016 at 7:38am
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My cad program came up with 1.109.
Sam
  
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SSShooter
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Re: Inscribed Octagon Dimensions
Reply #3 - Sep 29th, 2016 at 7:41am
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Thanks. Rule-of-thumb close, but not good enough for precision machine work. I'm using some trig to be exact (mill with indexing head is good to 0.005").
  

Glenn
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Deadeye Bly
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Re: Inscribed Octagon Dimensions
Reply #4 - Sep 29th, 2016 at 8:23am
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My MORSE Machinist Practical Guide booklet says diameter X .9239. Your barrel measures 1.250" at the breech end so you can mill an octagon 1.154" across the flats or anything smaller.

Check with Klinger to see what size his barrel is.
  
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marlinguy
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Re: Inscribed Octagon Dimensions
Reply #5 - Sep 29th, 2016 at 11:31am
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Glenn, would it help if I measured my original Hepburn Creedmoor barrel and posted the dimensions? I'm not a machinist, so can't begin to calculate the measurements you need.
  

Vall
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frnkeore
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Re: Inscribed Octagon Dimensions
Reply #6 - Sep 29th, 2016 at 12:25pm
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I either divide the diameter by 1.082 or multiply by .924 to get the across the flat size. To get the width of one flat, multiply diameter by .3826

Frank
  

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Chuckster
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Re: Inscribed Octagon Dimensions
Reply #7 - Sep 29th, 2016 at 12:36pm
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Frank and DB are correct.
Multiply the round diameter times the Cosine of 22.5 (.9239) to get the maximum distance across the flats for an octagon.
Chuck
  
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uscra112
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Re: Inscribed Octagon Dimensions
Reply #8 - Sep 29th, 2016 at 4:20pm
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nuclearcricket wrote on Sep 29th, 2016 at 7:38am:
My cad program came up with 1.109.
Sam


I cheated too.  My CAD says 1.10866 flat to flat.
  

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SSShooter
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Re: Inscribed Octagon Dimensions
Reply #9 - Sep 29th, 2016 at 8:54pm
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marlinguy wrote on Sep 29th, 2016 at 11:31am:
Glenn, would it help if I measured my original Hepburn Creedmoor barrel and posted the dimensions? I'm not a machinist, so can't begin to calculate the measurements you need.

Vall - that would be great. I've got dimensions from Tom Klinger's barrel which I'll post when I get home next week, but would be interesting to compare them. Could you let me know just in front of the receiver and at the end of the octagon and also the length of the octagon portion? Tom's rifle is a 34" long 44-100. Is yours the same? Thanks.

And, yes...... That cosine of 22.5 x the diameter is correct. Thanks to all.
« Last Edit: Oct 3rd, 2016 at 8:18am by SSShooter »  

Glenn
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marlinguy
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Re: Inscribed Octagon Dimensions
Reply #10 - Sep 30th, 2016 at 10:27am
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Glenn,
My Hepburn is not in what is considered a "Creedmoor caliber". Mine is a Match B with Creedmoor barrel marked "32 40 B&M" which is the standard .32-40 Ballard & Marlin cartridge.
My barrel is exactly 34", nothing slightly over. The octagon portion is exactly 12", and forearm cap ends even with the octagon portion. The octagon is .998" at the receiver, and .925" at the end of thhe octagon. Round is .984" at the start, and .737" at the crown. Front sight dovetail is @15/16" on center from the crown.
  

Vall
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SSShooter
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Re: Inscribed Octagon Dimensions
Reply #11 - Oct 3rd, 2016 at 5:41pm
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Vall - here are the measurements from Tom's original 44-100 Hepburn Creedmoor rifle, which I'm going to copy as best I can.

At the receiver the barrel measures 1.185 across the flats. At the front end of the octagonal section the flats measure 1.167. Then starts round at 1.162 and tapers to .870 at the muzzle. The octagonal section is 2.3 long.

As you can see, the octagonal section is only 2.3" in length. The 1.154" I can use will be close to the 1.185" of the original. The 0.018" of taper may be tricky. Will see next month when I get started on it.
« Last Edit: Oct 3rd, 2016 at 7:14pm by SSShooter »  

Glenn
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marlinguy
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Re: Inscribed Octagon Dimensions
Reply #12 - Oct 3rd, 2016 at 6:57pm
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I'm guessing the big differences in barrel diameters between the .44-100 and my .32-40 are due to bore sizes, and weight restrictions. The smaller bore requires more metal be removed or it wouldn't fall within the 10 lb. limit.
Just out of curiosity I measured my Ballard #7 Longrange in .44-100 to see how it compared to Tom's Hepburn. The Ballard is 1.160" at receiver and octagon is 11.375" long. End of octagon is 1.090" Round is .920" at the muzzle. Also 34" long Creedmoor length.

In looking at Tom Rowe's Hepburn book I see quite a variety of Creedmoor barrel shapes! A few with the short octagon section of Tom's gun. Some with half octagon barrels. And a few with Rigby flats also. And the military Creedmoor barrels in full round with all the military bands.
  

Vall
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Re: Inscribed Octagon Dimensions
Reply #13 - Mar 25th, 2017 at 12:27pm
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SSShooter wrote on Sep 29th, 2016 at 7:41am:
Thanks. Rule-of-thumb close, but not good enough for precision machine work. I'm using some trig to be exact (mill with indexing head is good to 0.005").


Going to loose some diameter to draw filing.

Terry
  

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