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Old December 29, 2020, 10:06 AM   #26
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Originally Posted by old roper View Post
Good article, thanks fo linking to it.
I’m thinking that most of that will become immaterial once photon torpedoes from Shiva-like lasers firing 16” “bullets” are allowed in competition.
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Old December 29, 2020, 10:29 AM   #27
Bart B.
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I've shot and watched both long, skinny barrels and long, fat barrels 30 inches in length shoot the same lot of 308 ammo equally accurate at long ranges.

Barrels start vibrating, mostly in the vertical plane, as soon as the bullet leaves the cartridge.

Some barrels have an adjustable weight near the muzzle to change its vibration frequency so bullets leave at angles to compensate for their velocity. Slower ones leave at higher angles than faster ones.
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Old December 29, 2020, 11:24 AM   #28
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HiBC,

You need to go to a highpower rifle match and watch the 300 yard rapid fire stages. They shoot 10 shots in 70 seconds reloading after the first few shots. Typically, 80% of the shots go into the 3" X ring. With bolt action rifles.

Or watch a 1000 yard prone match seeing 5 sighters then 20 record shots fired in 20 minutes and 3/4ths of them in the 10 inch X ring
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Old December 29, 2020, 12:47 PM   #29
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I don't doubt it,Bart. Thanks!.
Correct me if I'm wrong,but I'd guess the barrelmakers practice stress relief.and the hole goes pretty straight through the middle of the barrel (uniform wall sections)

I have a 30/338 with a Lilja #3 contour. Its n a 20 oz Hi-Tek stock.(OK,I added a few oz steel bedding the receiver,a Husky 5000 I trued on a surface grinder. It shoots 200 gr Accu-Bonds at 2900 fps quite well enough for my needs.
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Old December 29, 2020, 01:10 PM   #30
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F-Class open rifle 32" barrel

https://www.6mmbr.com/gunweek088.html
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Old December 29, 2020, 02:50 PM   #31
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Road clam,

Barrels start vibrating when the bullet starts down the barrel.

https://www.varmintal.com/aeste.htm
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Old December 29, 2020, 03:11 PM   #32
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I don't doubt it,Bart. Thanks!.
Correct me if I'm wrong,but I'd guess the barrelmakers practice stress relief.and the hole goes pretty straight through the middle of the barrel (uniform wall sections)
The process is called gun drilling. Barrel blank is spun on centers and the bore reamer is pushed into it. The reamer follows the blank center.
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Old December 29, 2020, 03:52 PM   #33
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Agreed Bart!! I have not run a gun drill,but I've done some relatively deep hole drilling.Like nearly 12 inches of 17-4 PH with a plain old 5/16 aircraft drill . I had abut 3/8 of the drill to chuck on. The lathe was a 15 in Colchester. It had IIRC,5 in of tailstock travel,and my true position tolerance for the entire length was .010. It was a production part. I did a bunch of them.

I have also looked through some respected name brand gun maker barrels that were visibly not straight. I've seen holes centered at the muzzle not centered at the breech.You won't see it on a custom barrel but you might on a Rugchestingtonage

Even when its not visible,there is a reason I put a best fit gauge pin inside the bore and use an indicator to center...and I have a spider on the other end of the spindle so both ends get dialed in.

Last edited by HiBC; December 29, 2020 at 04:01 PM.
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Old December 29, 2020, 05:48 PM   #34
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HiBC,

All of the USN top match grade 7.62 Garand barrels had about 35 pounds of down force on the barrel where the stock ferrule fit in the lower band. The barrels were bent a little yet tested 1/2 to 2/3 MOA at 600 yards with Sierra 190 HPMK's
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Old December 29, 2020, 06:12 PM   #35
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I saw that in a gun I tested for a friend. The barrel had a bend in it but it shot reasonably well and good enough for hunting.
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Old December 29, 2020, 06:45 PM   #36
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I just bought a 116 savage heavy barrel SS just love the gun 7mm mag a friend had it, was not sure about the heavy barrel I think it was a great buy !!!
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Old December 29, 2020, 07:23 PM   #37
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All of the USN top match grade 7.62 Garand barrels had about 35 pounds of down force on the barrel where the stock ferrule fit in the lower band. The barrels were bent a little yet tested 1/2 to 2/3 MOA at 600 yards with Sierra 190 HPMK's
I'm happy to learn. Thanks!

I can see where if you can't free float it,preload it.
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Old December 29, 2020, 09:58 PM   #38
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Always new things

http://bulletin.accurateshooter.com/tag/barrel-block/
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Old December 29, 2020, 11:05 PM   #39
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still waiting for someone to tell me how varmint hunting isn't hunting...
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Old December 30, 2020, 12:05 PM   #40
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Here in Co to shoot elk we need Big Game License and shoot PD we need Small Game License. I have both to hunt.
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Old December 30, 2020, 03:50 PM   #41
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still waiting for someone to tell me how varmint hunting isn't hunting..
Unless you eat it, its not hunting.

I am not saying removing varmints is not usefull, but unless you eat them thar varmints its a category of several categories unto itself.

My relatives shoot gophers as they are a pest (holes in the pasture, broken legs, lower pasture yield maybe as if there is not grass growing it takes off the carrying capacity.
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Old December 30, 2020, 11:03 PM   #42
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Unless you eat it, its not hunting.
Ok, thanks for letting me know your definition. I disagree, respectfully..
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Old December 31, 2020, 08:36 PM   #43
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I've hunted varmints for about 55 years, so don't try to tell me it's not hunting.
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Old January 1, 2021, 01:28 PM   #44
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Originally Posted by Bart B.
Road clam,

Barrels start vibrating when the bullet starts down the barrel.

https://www.varmintal.com/aeste.htm
You are correct, and I do know this , I should have been more precise language in my post. Edited my original post to clarify, good catch.

As stated in the article I understand in "theory" you want the barrel whip sine wave on the "increase" vertically as the bullit exits the barrel for maximum consistency. The bullitt exiting the barrel on the downward sine wave whip is not good. Barrel sine waves and harmonics are another whole accuracy debate that's way above my pay grade !

Bart B. you might find this interesting (unless you already know) . Interestingly I did learn how to test my 1874 Sharps 45-70's barrel for the harmonic "sweet spot". The "sweet spot " is the area where you can rest the barrel on a rigid support and NOT have harmonics affect your consistency.


http://www.texas-mac.com/Minimizing_...weet_Spot.html
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Old January 1, 2021, 04:22 PM   #45
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Road Clam,

According to https://www.varmintal.com/amode.htm there is no sweet zero vibration spot.

And your linked mode harmonic frequencies are not even multiples of the resonate frequency. Besides, your link shows both ends fixed. Only one end of rifle barrels are fixed.

Last edited by Bart B.; January 1, 2021 at 04:52 PM.
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Old January 1, 2021, 05:41 PM   #46
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According to https://www.varmintal.com/amode.htm there is no sweet zero vibration spot.
I read the article--very interesting. I didn't see where he concluded that there was no sweet spot in the vibration. Is that in another article?
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Old January 2, 2021, 02:51 PM   #47
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I read the article--very interesting. I didn't see where he concluded that there was no sweet spot in the vibration. Is that in another article?
Read the other articles and see if any list sweet spots.

Sweet spots happen when the harmonic frequencies are whole multiples of the fundamental resonant frequency. There aren't any.

However there can be a place where the barrel can rest where the vibration amplitude is minimal and may be the best place.

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Old January 2, 2021, 04:25 PM   #48
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And the Houston Gun club said 22 inches was the ideal length.

I doubt anyone really knows as each barrel is a bit different.
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Old January 2, 2021, 06:16 PM   #49
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The oft time mentioned article on the Houston warehouse says the barrel MUST be 21 3/4” long for optimum accuracy. That precise length sets up a vibration pattern that duplicates well from shot to shot.

All barrel's vibration patterns are repeatable from shot to shot. The barrel's dimensions are the same for each shot.
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Old January 2, 2021, 09:22 PM   #50
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Sweet spots happen when the harmonic frequencies are whole multiples of the fundamental resonant frequency. There aren't any.
That would be a perfect sweet spot, but in practice all you need is for the vibration frequencies that have significant amplitude at the muzzle at bullet exit to cooperate and then you get a decent sweet spot.

Realistically this probably doesn't happen at a node (a point where the sum of the instantaneous vibration amplitude at the muzzle is at zero or a minimum), but rather at an anti-node. Where the amplitude of the vibration is maximum, that's where the muzzle movement is at minimum velocity. You don't care so much where the muzzle is (as long as it's more or less in the same place every time), the important thing is that it's not moving very fast when the bullet exits.

The article correctly shows that there are a lot of complex things going on, but the visualizations have the amplitudes set up so that they are easy to see and examine, they don't have amplitudes that are scaled relative to each other. The article refers to this briefly when it comments that "The higher frequency modes have extremely small amplitudes..."

Another point to keep in mind is that the low frequency vibration modes are moving the muzzle very slowly in terms of bullet motion and it would not be especially important to try to tune for a spot where the muzzle velocity (velocity of the muzzle) due to those modes is a minimum because the motion is so slow due to those modes that it won't affect the point of impact significantly even if bullet exit happens at a relatively inopportune time.

So, in his example, Modes 1 & 2 are moving the muzzle relatively slowly relative to the bullet motion, according to his commentary, and the "higher frequency modes" have extremely small amplitudes". He doesn't tell us where the numerical cutoff for "higher frequency" is, but let's say it's only the top two for the sake of argument.

Now we have 4 out of the 8 modes remaining that we need to worry about. Modes 4 and 6 are stretching and twisting modes, which hardly move the muzzle at all in the target plane. That leaves us with Modes 3 and 5. Even assuming that Modes 3 and 5 have similar amplitudes (which is unlikely to be true) the frequency of Mode 5 is about double that of Mode 3--close enough that they could easily be in relatively close sync--close enough that we could reasonably expect a practically significant (though obviously not perfect) sweet spot.

If their amplitudes are quite different, then we could just focus on the one that's larger and ignore the smaller one when we are looking for our sweet spot.

But either way, there's a good chance we'll be able to find a place where the velocity of the muzzle in the target plane is minimum at bullet exit.

In other words, there may be a lot of complex things going on, but it's not just possible, it's actually probable, that only one or two of the vibration frequencies are going to be affecting the muzzle motion/position significantly at the point of bullet exit.
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However there can be a place where the barrel can rest where the vibration amplitude is minimal and may be the best place.
Well, as mentioned above, it's probably not the point where the vibration amplitude is minimal but rather where the velocity of the muzzle motion in the target plane is minimal. But that's correct. Most would call that the sweet spot. I don't believe there's really a formal definition of "sweet spot" that implies it's the absolute ideal from a theoretical standpoint. It's a fairly general term that means a point that gives good results.
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