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Barrel Length 300 win Mag

 
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  #22  
Old 05-29-2012, 12:26 PM
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Re: Barrel Length 300 win Mag

Quote:
Originally Posted by Bart B View Post
Using Lilja's 27 inch No. 7 contour dimensions from Lilja's web site, here's what my software calculated for those two 30 caliber barrel lengths before chambering:

No. 7 contour shortened to 26 inches vibrates at 58.40 Hz.

No. 7 contour shortened to 21 inches vibrates at 90.67 Hz.

To me, that's only a bit over 55% stiffer, not 275% stiffer.

Chambering makes them a bit more flexible 'cause metal's been removed at their back end.
that part you'll have to take up with Lilja himself. But as I said before, I did a similar test with a different kind of metal and saw similar results (albeit not 2.75 times stiffer [ if I remember right I saw something in the area of twice the deflection]). Remember that Dan was measuring actual movement of the barrel, and had nothing to do with harmonics

Now I don't remember what the bore size he had in the barrel (if he even stated it), or even if it had a chamber in it. My test did not use a threaded shoulder to retain the barrel. I used a heavyduty vee block that was anchored down on the table top of a SIP jigbore. The Mallory Metal was actually placed in a mesh bag and then hung on the steel with wire. I then used a surface gauge with a dial indicator to confirm flex. The vee block had two clamps hold the steel in place that were about five inches apart. I know for a fact that the table top was flat, as I scraped it to less than .0002" in six feet.
gary
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  #23  
Old 05-29-2012, 02:34 PM
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Re: Barrel Length 300 win Mag

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Originally Posted by Trickymissfit View Post
as I said before, I did a similar test with a different kind of metal and saw similar results (albeit not 2.75 times stiffer [ if I remember right I saw something in the area of twice the deflection]). Remember that Dan was measuring actual movement of the barrel, and had nothing to do with harmonics.
Dan Lilja may have been measuring barrel droop; how much the barrel's muzzle goes down from gravity as its held in a receiver.

My software calculates the barrel's resonant frequency it whips at as held by the receiver. Just like a fishing pole whips or vibrates as it's held and wiggled by ones hand. That's what happens to a barrel when its shot. Harmonics are even multiples of the resonant frequency and they wiggle the barrel at much lesser amounts than the fundamental one that causes the most angular movement of the bore axis at the muzzle. The amplitude of the stiffer barrel's wiggling will be much less than the more flimsy barrel's, too.
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  #24  
Old 05-30-2012, 05:37 AM
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Re: Barrel Length 300 win Mag

Regarding your comments:
Quote:
Dan Lilja did a paper on the subject a few years back. His method of figuring the deflection was somewhat crude, but still reliable.

Remember that Dan was measuring actual movement of the barrel, and had nothing to do with harmonics'

Later in I did my own test with a piece of 1" diameter 17PH-4 steel that I had the bore gun drilled to .250" for another project. I used a simple ten pound weight, and checked it every two inches. I saw similar results in that the closer I got to the anchoring point the stiffer the barrel was.
How much a horizontally placed barrel bends/droops at some point along its length with a weight hanging on it is definitely related to how stiff it is and that is directly related to the frequency it naturally vibrates at. And its natural frequency determines what the harmonics will be.

How much it bends in a static position from a weight hanging on it will be different than when a round's fired in it. It bends only down from straight out with a weight on it. It bends in all directions when a round's fired in it, but most of the bending's up and down. How much it bends depends on how powerful the ammo is and how heavy the weight is. But one thing's constant for every round fired for a given angle the barrel's aimed at; how much it droops (bends down) from its own weight so it doesn't matter how much that is.
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  #25  
Old 05-30-2012, 10:52 AM
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Re: Barrel Length 300 win Mag

Quote:
Originally Posted by Bart B View Post
Dan Lilja may have been measuring barrel droop; how much the barrel's muzzle goes down from gravity as its held in a receiver.

My software calculates the barrel's resonant frequency it whips at as held by the receiver. Just like a fishing pole whips or vibrates as it's held and wiggled by ones hand. That's what happens to a barrel when its shot. Harmonics are even multiples of the resonant frequency and they wiggle the barrel at much lesser amounts than the fundamental one that causes the most angular movement of the bore axis at the muzzle. The amplitude of the stiffer barrel's wiggling will be much less than the more flimsy barrel's, too.
Bart, I think we were compairing different things that come back together at another point in time. The rigidity issue also effects the barrel harmonics as you certainly point out (correctly by the way). Years back I did some rather crude experimenting with barrel pressure points and counteracting barrel harmonics. The results were an improvement, but also not as much as I'd hoped for. I now know that I was on the right track, but just in the wrong location.

I've also learned that the diameter and weight of the barrel can also be reduced via the shape of things. This came out of trying to figure out if barrel fluting actually would add to barrel stiffness. I found that it can, but the added stiffness is so minute that it's not worth figuring into the equation (plus it creates other problems that more than counter act against them). I've no came to the conclusion that the old chrome moly barrel can be made to shoot more accurately with the proper heat treat and machine work of course. One experiment I did was with several blanks of steel that were of the same alloy number (I know it also has it's own errors with that method). I compaired 1" diameter ground 4150 steel with 1" hex, 1" octagon , and 1" ten sided bar stock that was machined. The hexagonial, octagonial, and decagonial stuff was stiffer. As in noticably stiffer. I then took the 1" round stuff and nitrided the O.D. to about .035" depth to have a 64Rc. That piece of steel was stiffer than the others
gary
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  #26  
Old 05-30-2012, 11:02 AM
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Re: Barrel Length 300 win Mag

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Originally Posted by Trickymissfit View Post
I've also learned that the diameter and weight of the barrel can also be reduced via the shape of things. This came out of trying to figure out if barrel fluting actually would add to barrel stiffness. I found that it can, but the added stiffness is so minute that it's not worth figuring into the equation (plus it creates other problems that more than counter act against them).
It's physically impossible to flute an existing barrel and make it stiffer; even by the tiniest amount. Fluting it removes metal that helped make it as stiff as it originally was. After fluting, there's less metal to resist compression and expansion from bending it.

However, a fluted barrel with the same length and weight as a solid one will be stiffer than the solid one. But its diameter is bigger.
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  #27  
Old 05-30-2012, 02:23 PM
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Re: Barrel Length 300 win Mag

Quote:
Originally Posted by Bart B View Post
It's physically impossible to flute an existing barrel and make it stiffer; even by the tiniest amount. Fluting it removes metal that helped make it as stiff as it originally was. After fluting, there's less metal to resist compression and expansion from bending it.

However, a fluted barrel with the same length and weight as a solid one will be stiffer than the solid one. But its diameter is bigger.
you are right, but it can be done as well. If your machining the flutes in a piece of steel by itself your right. But you can then do a couple things to add a compressive stress into the metal surface that will make it every so slightly stiffer (and I do mean slightly!). But in the end all you've done is open the bore up in the process. Ideally a spline could be rolled into the barrel surface I guess, and then finish out the bore, but I've never seen a spline roller capable of doing two foot or longer surfaces. So in the end it's a moote point. The problem with milling splines is the the circular motion of the cutter will create more problems than anybody cares to have. In something like a planer it would be better I suppose.
gary
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