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md5200
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highwall barrel harmonics
Jul 29th, 2010 at 11:06pm
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i have an old highwall that i've had rebarreled to a 240 cobra. we used a very high quality barrel and the fit and workmanship is top drawer. however this rifle seems to be very picky and i keep thinking its all in the forearm, but i'm not sure the barrel is 30 in long and a little over 1 in at the muzzel. i'm wondering if a bolt on sled would help or a tuner of some sort. i'd like to hear any ideas. oh the rifle seems to want to string vertically. thanks md5200
  
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westerner
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Re: highwall barrel harmonics
Reply #1 - Jul 30th, 2010 at 12:11am
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Butt stock inletting nice and tight? 


            Joe.   Smiley
  

If a waffle falls over on a breakfast table and no one is there to hear it, did the waffle make a sound?
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md5200
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Re: highwall barrel harmonics
Reply #2 - Jul 30th, 2010 at 12:12am
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since my post i've found several posts on tapping the barrel. what is the sound one is looking for? does it matter if the barrel is naked or not? also the use of talcom powder, how would it work on a round barrel? also i have a 1 in 8 twist so i think the nodes are shorter and that is why i'm having trouble finding the sweet spot. i think i will try a solid rest at different spacing and see what happens. i hope someone has some ideas. also it seems to me that forearm fit might not be as critical if a person can find the sweet spot and use that for a resting point on the barrel. thanks guys md5200
  
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John Boy
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Re: highwall barrel harmonics
Reply #3 - Jul 30th, 2010 at 1:17am
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MD, the sound you are trying to determine for the null point is a dull thud compared to the 'ringing' sound that is not the null point ... with the forearm removed

I'm the poster on the boards of the talcum powder method.  Learned it from an old gunsmith.  Works on octagonal barrels but not on round ones because the powder won't stay on the barrel when ones pulls the trigger.  Grin

Read this post on Shiloh Rifle on what to do with round barrels:

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As a reason why you have vertical stringing, a good possibility that the harmonic amplitude arc is on the up swing when the bullet is leaving the bore.  Find your null point and then shoot some groups with the barrel rested on the null and see if your stringing decreases.  Be sure to let the rifle do a normal recoil too without trying to do a lead sled shot

I believe you are using a nitro based powder for this Cobra.  Harmonics are effected by the powder type too:
# Powder burn rate too slow for the bullet.
# Bullet weight too light for the powder's burn rate.
Something else to consider ... great fun isn't trying to shoot one holers!  Wink
« Last Edit: Jul 30th, 2010 at 1:25am by John Boy »  

Regards
John
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MartiniBelgian
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Re: highwall barrel harmonics
Reply #4 - Jul 30th, 2010 at 2:57am
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MD,

Just try the ladder method for load development - that way, I got a modest .22 Hornet to be a pretty good sub-MOA tackdriver.  And - don't forget consistency in shooting technique matters quite a bit with these small calibres!
  
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Re: highwall barrel harmonics
Reply #5 - Jul 30th, 2010 at 4:44am
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MD,
  The bolt-on sled will act like a tuner. Move it to find the sweet spot on the barrel. Make sure the forearm isn't touching the front of the receiver. Change one thing at a time and keep trying. I've got a .219 Wasp and an  Ackley Improved Zipper (barreled by Ackley) on Highwall actions that are more like redheads than rifles but when you find what they like, it's a joy to behold.
                                                       Steve
  
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md5200
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Re: highwall barrel harmonics
Reply #6 - Jul 30th, 2010 at 11:11pm
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first i'd thank everyone for their input. all very helpful. for a place to start we used the stethascope method and determine the starting place to be about 6 in back from the muzzel. i made a copy of the wood bob sled. i have some bullets(can't say mfg) that i have never been able to get past the pattern stage, since they were all i had not much choice but to use them. i had a new can of powder that probably was'nt the most suitable, but again its what i had. i shot 3 shot groups and the first was 3 to 4 in and kind of round. imoved the sled back about 1/2 of an in and it came down in size. by the 12th and 15th shot the groups were slightly over a quarter in size. man am i impressed, this is almost like magic. i'm wondering if i set the butt on a bag just as if i were shooting and set the end of the barrel on a set of scales and got a weight and then made a slipon weight that size would it work? the reason i ask is the sled would be hard to use over the hood. again thanks guys and if you happen to think of something to try let me know. thanks md steve you are right on the money about the redheads
  
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