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Old March 6, 2015, 05:47 PM   #1
Shooter2675
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Importance of Barrel Thickness

I am wondering how much the thickness of a stainless steel barrel would effect accuracy. If I were to buy a .300 win mag with a 24 inch barrel that is a sporter contour (Savage barrel, so that means end diameter of 0.565 inches), how much more inaccurate/accurate would it be versus the same barrel in a bull contour or a Varmintngt contour. Also, how would the thickness effect barrel heat-up?

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Old March 6, 2015, 06:53 PM   #2
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how much the thickness of a stainless steel barrel would effect accuracy
It has nothing to do with the potential "accuracy" IF you let the barrel cool between shots
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Old March 6, 2015, 07:57 PM   #3
Shooter2675
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How long should I let it cool after each shot?

John
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Old March 6, 2015, 08:10 PM   #4
Bart B.
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If it is a good barrel properly fit to the receiver, it can shoot several times a minute for a few dozen shots into 1/4 MOA at 100 yards. A barrel that walks shots away from point of aim is fit to a receiver whose face isn't squared up with the barrel thread axis.

Barrel thickness has virtually zero effect on the accuracy its chamber and bore can produce. Each barrel vibrates at its unique frequency and harmonics thereof; exactly the same for each shot. It's the most repeatable thing in the whole system comprising ammo, rifle and shooter. Everything else has variables.

Thinner barrels heat up and cool down faster than thick ones.

Last edited by Bart B.; March 6, 2015 at 08:21 PM.
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Old March 6, 2015, 08:19 PM   #5
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Thank you so much for your help, Snyper and Bart B. Does anyone know what kind of accuracy could be expected from a Savage 116 Stainless .300 win mag trophy hunter xp?

Thanks,

John
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Old March 6, 2015, 08:36 PM   #6
Bart B.
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Clamped in a free recoiling machine rest and fed Black Hills match ammo, it may well shoot inside 1/2" at 100 yards for a few shots. Held against ones shoulder resting atop something on a bench top, anywhere from 3/4" to 2" at 100 yards with the same ammo, depending on who is shooting it.
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Old March 6, 2015, 08:38 PM   #7
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The main purpose of the heavier barrel is to add weight, and to change the balance. The rifle isn't really any more accurate, but most shooters can shoot them more accurately.

Most sporter weight rifles will come in at around 8-9 lbs once scoped and ready to hunt with. A longer, heavier barrel will push that to 10-12 lbs, sometimes more. It is usually easier to hold the heavier rifle steady as the trigger is pulled, but for most people the difference in accuracy isn't worth the added weight.

There are some real ultra-lights out there that weigh under 6 lbs. They have the potential to be just as accurate as a 12 lb rifle, but are unforgiving of less than perfect shooting form.

Barts post is accurate as usual, BUT, you'll find that most factory barrels will heat up after a few shots and start to open up group size. To get a perfect barrel, fitted perfectly to a receiver is usually something done in a custom shop. Common factory rifles and barrels will usually put 3 shots into some pretty small groups before needing to cool. Which I don't see as a handicap at all on a hunting rifle. I've never needed that many shots.
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Old March 6, 2015, 10:32 PM   #8
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I all of us have seen featherweight barrels that shot tiny groups and would do so all day, and heavy "Bull" barrels that sprayed bullets all over the countryside. There is no way anyone can tell you what size groups you will get with any given rifle/ammo combination.

And then there are factors other than the barrel and the rifle, like the nut that holds the rifle.

Jim
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Old March 7, 2015, 08:45 AM   #9
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The "donor action" for my 7-08 LR rifle came from an older Savage lightweight mountain rifle (FM Sierra) ...20", light contour barrel that coincidentally was in 7-08- and shot cloverleafs at 100 yards with 150 SMK's.

It really sucked pulling that barrel (it would as most, start stringing when it got hot and wasn't suited for benchrest)- but I'm sure the guy that bought it for his hunting rifle was pleased.
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Old March 7, 2015, 09:07 AM   #10
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Quote:
Does anyone know what kind of accuracy could be expected from a Savage 116 Stainless .300 win mag trophy hunter xp?
No one can predict how accurate a particular barrel will be

The only way to know is shoot it with the load you want to use

Most modern rifles will shoot sub-MOA once you find a load it likes.

There are too many variables to try and guess
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Old March 8, 2015, 08:07 AM   #11
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Most modern bolt action rifles will shoot sub MOA at 100 yards with one or two specific loads. You don't have to try different handload recipes. Buy a box of Federal or Black Hills or even Hornady match ammo and shoot it. The accuracy's there whether or not you can uncover it. You can also duplicate those loads with new components and they'll do as well; properly assembled.

We need to remember that 99.9% of all accuracy claims are really how accurate someone shoot a given rifle and load. Any given rifle and load combination will have a wide range of accuracy levels across several people shooting them. The rifle and its ammo has to be shot free recoil to asses their performance without human intervention.

I've had no issues predicting how accurate a barrel would shoot. Never worked up a load for most of them I wore out. Just used the same recipe in each one for the same cartridge. They all shot as predicted.

Last edited by Bart B.; March 8, 2015 at 08:41 AM.
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Old March 8, 2015, 10:16 AM   #12
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Thin barrels may be accurate. Depending on the barrel, as it heats up through sustained firing, it can start to whip and the point of impact will shift. Hence the advantage of the heavier barrel. They tend to be less affected by the heat. Solution? If you're shooting a slender barrel, give it time to cool off. I did this with an earlier Mini-14 and it was able to hit stationary clay pigeons at 100 yards. I spoke with a hunter who told me his gun consistently shifted its point of impact as the barrel heated. I told him it was the nature of his barrel and that sporter barrels tended to do that.
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Old March 8, 2015, 01:10 PM   #13
Bart B.
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Rifle barrels whip the same amount and frequency every time they're fired for a given load regardless of their temperature. The amount will change with powder charges; more with more, less with less. One doesn't heat them up enough to change their frequency and amount for a given load. By that time, the barrel would be too soft to contain the pressure and it would let bad things happen.

Any barrel regardless of shape or weight will change point of impact as it heats up if it's not fit to squared up receiver faces. A high spot on the receiver face puts a stress line in the barrel at that point.

Competitive service rifle shooters putting 24 rounds down range in 50 seconds shooting the National Infantry Trophy Match see no point of impact change from the first to the last shot starting with a cold, thin service rifle barrel. Nor do bolt gun competitors see point of impact change shooting 10 shots in 60 or 70 seconds shooting two strings of that two minutes apart; again, starting out with a cold barrel.

Putting 25 to 30 shots once every 20 to 30 seconds in 30 caliber magnums have shown no change of impact at 1000 yards as barrels heat up from ambient temperature.

Lake City Arsenal's 30 caliber match ammo showed no point of impact change starting with a cold barrel through 270 rounds later fired once every 20 seconds or so at the 600 yard test targets.

Nor do benchresters see their shot impact walk shooting once every 10 to 15 seconds putting a 10-shot string into a 1000 yard target when wind conditions are stable; a popular thing to do; those barrels really get hot.

Last edited by Bart B.; March 8, 2015 at 01:22 PM.
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Old March 8, 2015, 02:39 PM   #14
Dixie Gunsmithing
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Barrel whip, or resonance, is from shooting the exact type of ammo, (charge, bullet weight, etc), that will cause a barrel to set up a vibration. Changing ammo, barrel shortening, or adding weight to the barrel, at a certain spot, can cancel it. Heat, though, can make a barrel draw, or bend slightly, and it generally does it in the same direction, each time, due to some internal stress. Though, they need to get pretty hot to do it. Heat can also cause problems, if a forend is not relieved or the barrel floated, where the barrel swells, due to heat, and makes contact with the wood.
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Old March 8, 2015, 03:08 PM   #15
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I'll second Bart's point about the squared action. If the barrel is tighter on one side of the shoulder (or barrel nut, for the Savage), then the differential expansion will tend to turn the muzzle slightly to the side. However, you must also have barrel floating in the stock's barrel channel so that contact with the stock can't throw this advantage away. A stock that uses strong up (O'Connor 2-point) or down (M1 Garand match or M14 match) stock pressure on part of the barrel is constrained more and swings up and down less (the downside of barrel floating).

In principle, heavy barrels have three advantages in addition to helping the shooter stabilize his position. One is that they heat more slowly, so that if there is a serious heat walking issue, it doesn't come on as soon, and goes away more gradually.

The second factor is they are more rigid. The rigidity of either a solid cylinder or one with a fixed bore diameter increases as the square of the square (fourth power) of the increase in outside diameter. So it doesn't take much additional thickness to significantly reduce the amount of recoil induced bending deflection near the muzzle. This results in smaller ringing amplitude as well.

The third factor is that heavy barrel profiles are more straight and have less difference between their diameters over the chamber throat and at the muzzle. This matters for some manufacturing processes. If your barrel blank was stress-relieved before contouring, as Douglas does, for example, or if it was hand lapped after rifling, or if it was hammer forged, this doesn't matter. But if it started out as a typical button rifled or broach cut full diameter blank and was not stress relieved before contouring, residual stresses from boring and rifling will cause the bore to expand a little where the profile is cut thinnest (at the muzzle). I've slugged a good number of military and low cost commercial Garand barrels, and every one of them could be felt tightening up as the slug moved from the muzzle to the thicker portion of the contour below the lower band shoulder. Having a barrel that is narrower at the breech end than at the muzzle is not conducive to best precision and can be disastrous with cast bullets.

All that said, are you going to have a great shooter just because the barrel is heavy? Of course not. It's just one factor that can make precision easier to achieve if all else is equal. If you have a gun that needs the lugs lapped, the stock bedded, or the barrel floated or re-crowned, the precision of the gun can be off. Not to mention that a bad sight or a need to improve the shooter's skills can always spoil the effort.
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Old March 8, 2015, 05:04 PM   #16
Bart B.
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Dixie, no mechanical engineering formula has an input for shock level (what's caused by different loads) to calculate the resonant frequency for a metal tube; rifle barrel, if you wish. They start vibrating when the firing pin falls and strikes the primer before it detonates and burns the powder. Only the magnitude, or amount of barrel whip and vibration changes with different loads. A metal tube's resonant frequency is determined by its metal properties and shape, not how hard it's smacked into vibrating. Otherwise, piano strings would make different notes for different amounts of hammer impact on them; they don't.

Check out Varmint Al's website's link to barrel vibration: www.varmintal.com. and look at these pages:

Esten's Rifle & Tuner
Light Rifle & Tuner
Barrel Harmonic Movie
Barrel Tuner Analysis
6PPC Barrel Dynamics

Adding a weight to a barrel at some point changes the resonant frequency. And that changes where in the muzzle whip cycle (whose frequency that determines bullet exit angle is at the 3rd or 4th harmonic of the resonant one) the bullet exits. That's how some barrels are tuned by a sliding weight at the muzzle to make a specific load shoot to point of aim downrange by letting the faster bullets leave sooner on the muzzle axis up swing and need less compensation for bullet drop than slower ones leaving later.

Once the barreled acction's clamped into a stock, the frequency the barrel whips at changes a bit as one end's fixed. The amplitude's also varied by how far the bore axis is above the butt plate contact point on the shooter; the higher it is, the more whip amount in the vertical axis there is, but the vibrating frequency is still the same.

Barrel whip and vibration cannot be cancelled, only changed in its parameters.

Last edited by Bart B.; March 8, 2015 at 05:20 PM.
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Old March 8, 2015, 06:26 PM   #17
Dixie Gunsmithing
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Bart, no it has nothing to do with how hard the barrel takes the lick of the charge, but the speed and the type of bullet traveling through it. It works similar to an automobile traveling at a certain speed, which runs off the road onto those wake-up bumps. If hit at the correct speed, the springs become resonant, and will continue to vibrate even though the auto is steered back onto the road. If the auto is traveling at a speed slower or faster than that, it will not set up the resonance. Another example is a wheel out of balance. After the wheel gains enough RPM, or a certain speed, the wheel will start to vibrate, then quit as the speed gets higher. It has to do with that notch speed. In essence, the speed is tuning the mechanical item at its resonant frequency. In a rifle, or any gun really, the bullets speed through the bore will trigger the resonance, if it goes through it at the proper FPM for that particular barrel.

I worked on a customers Remington 700 once, which was a .22-250. With regular off the shelf ammo, that he provided, and the barrel would sing like a tuning fork, for what seemed like thirty seconds, after firing it. Changing the type of ammo fixed the problem. All it did, was change the speed of the bullet, by using ammo that was faster in FPM. Lower speed would have worked too.
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Old March 8, 2015, 09:17 PM   #18
Bart B.
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Dixie, I disagree with your explanation of when and how barrels vibrate. It's physically impossible. They vibrate at their own natural frequency (as modfied by the receiver attached) if the stock's smacked hard on it fore end tip. For a given rifle, the bullets time in the barrel determines where in its whip cycle it exits at. The barrel whips at exactly the same frequncy for each shot; it's properties do not change with every shot.
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Old March 9, 2015, 07:47 AM   #19
Dixie Gunsmithing
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Bart, you are misunderstanding me. How long the bullet stays in the barrel, is the same thing as its speed in FPM. That is the point at which will cause it to resonate at its natural frequency. By shortening a barrel, or adding a weight, moves that frequency, but so will a bullets speed.
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Old March 9, 2015, 08:12 AM   #20
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Depending on the load, time in the barrel could be constant but muzzle velocity will not be. It's also possible for muzzle velocity to be constant and barrel time different across different loads. It all depends on the area under the load's pressure curve.

While different dimensions of a given barrel will change its resonant frequency, the velocity a bullet leaves will not. That's because a given barrel has the same physical/mechanical properties for all shots fired regardless of their peak pressure, barrel time or muzzle velocity. If the barrel really did vibrate differently for different muzzle velocities, that would play havoc with down range accuracy.

Here's an on line site that calculates rifle vibrations so you can see where a bullet leaves on its muzzle axis angle at end of barrel time:

http://www.geoffrey-kolbe.com/articl...vibrations.htm

Show me a formula for calculating barrel resonant frequency that has an input for muzzle velocity and I'll agree with you. Please explain the mechanics of how muzzle velocity changes the frequency a barrel vibrates at. Do you think the frequency goes higher with faster bullets?

I asked a mechanical engineer (whose business is vibration analysis) some years ago to write a program to calculate a barrel's resonant frequency. The only inputs were bore diameter, steel type, both ends free or breech end fixed (in a receiver clamped in a stock) profile diameters and lengths along the barrel. No input for bullet velocity was used because that's not part of the formula. It's available at Tom Irvine's site:

http://www.vibrationdata.com/StructuralFE.htm

It's rifle_frequency.exe

If you're absolutely positive that muzzle velocity will change a barrel's resonant frequency, challenge him to fix his software to include an input for muzzle velocity. Then contact Varmint Al at www.varmintal.com and have that engineer fix his finite element software that calculates all sorts of barrel vibrating stuff to include muzzle velocity calculating a barrel's resonant frequency as well as the whole rifle's vibration patterns.

Last edited by Bart B.; March 9, 2015 at 10:46 AM.
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