I heard that an "accurate load" is but a consistent load that exit the muzzle of a specific gun at the top or bottom of the barrel whip, so I wanted to find out more about barrel vibration...

But there seem to be only one serious article about barrel vibration on the internet...Is there some place where I can find out more?

How many methods/gadgets out there are for "tuning" vibrations? Any way to "reduce" vibrations besides gaining weight to the barrel?

Thanks in advance.

Pyrotech, either you are going to get few responses or a couple dozen to your question, (about barrel vibrations and it's effect on accuracy). The Boss system attempts to do what you are getting at. I've been told that the German rifle builders studied this topic considerably when they were putting steps in military barrels over 100 years ago. Using slide rules and such they were pretty adept at it and they set the standard for accuracy in military rifles. Personally, I believe barrel vibration is a major factor in why some loads are accurate in a rifle and others aren't. For example, identical bullets and load compontents except for powder. Both loads achieve nearly identical velocity. One shoots under and inch, the other shoots over 2 inches. Why? Yes, the powders have a different burn rate/pressure curve, but 24 inches later the projectile is going the same speed. I conclude that the burn rate/pressure curve causes different vibrations on the barrel, hence result in different accuracy.

When the powder begins to burn, it creates a shock wave that travels through the rifle at the speed of sound. In steel, the speed of sound is about 10X what it is in air, so the shock wave reaches the muzzle before the bullet does.

For a simple case, think about what happens if the muzzle is vibrating in an elliptical (oval) pattern. At the ends of the ellipse, the muzzle is moving the slowest. On the sides of the ellipse, it is moving the fastest.

If bullets exit the muzzle when it is near one of the ends of the ellipse, small variations in the time it takes the bullet to travel down the barrel will produce small variations in point of impact. If it exits while the muzzle is on the side of the ellipse, small variations in the time it takes the bullet to travel down the barrel will produce large variations in the point of impact.

So, as previously stated, the objective is to time the bullet's travel so that it exits when the barrel is not moving much.

One fellow that shoots at the same range I do took a 3/8" piece of steel, and bored two holes in it: one the OD of his barrel, and the other large enough to accomodate a 3/4" bolt. He cut a slit through to the hole the size of his barrel, and drilled and tapped for small cross screw to close the slit, so the steel could be clamped to his barrel. The other hole, he tapped for a 3/4" bolt. He installed a bolt, and put a nut on to lock it in place. This whole assembly is then used to tune the resonant frequency of the barrel, just like the BOSS... just give the bolt a quarter turn at a time, then tighten the nut to keep it in place. He said he was getting very good results.

The other alternative is to fiddle slightly with the powder charge and bullet seating depth to get the transit time exactly right.

There are a lot of issues here, but one theory is that each rifle has a natural frequency. When the shell goes off it "rings" the rifle like a tuning fork. This view explains why some loaders put a lot of faith in the importance of "barrel time" or how long it takes the bullet to exit. If they find a sweet spot, another load with the same barrel time should leave the barrel at the same sweet spot, even though bullet weight and powder may be different.

The frequency of vibration can be tuned by changing the length or weight of the barrel, by changing the length of barrel bedded, and by adding an upward pressure point near the forend. I don't trust this latter method in a wooden stock due to humidity changes.

Don

[This message has been edited by Don G (edited 12-28-2001).]

The computer program "Quik-Load" will indicate "barrel-time" for each load you enter and the key is that when you find a load you like you try other loads in the program to get similar barrel times.

The proper term is barrel harmonics. The thinner the barrel the greater the effect. Barrel fluting and heaver contours can greatly limit barrel whip. It can be altered through load development, bedding, hanging weights of the end of the barrel a.k.a. BOSS system, or by relieving barrel stress. Barrels have stress built into them during the cutting process. One of the ways to eliminate this stress is though cryo treatment.

The cryogenic process relieves inherent stress within the steal resulting in uniform harmonics. While a lot of this is voodoo, cryo treatment can fix some accuracy problems. By simply manipulating powder charges and pressures, one can tune harmonics to the bullet. There are a lot of other accuracy gremlins that have greater impact than harmonics, however, it is something to consider.

I think those gremlins have an active colony in my gun vault! Just about the time I think I've got it figured out the Gremlins make an appearance to remind me how little I know.

Here's a question: I read once a gun writer of pretty good reputation (Don Zutz?) that he saw a gunsmith do a thing with powerful magnets on a shotgun barrel and change the pattern density. The gun was patterned before and immediately after while this procedure was witnessed and performed. The 'smith claimed it had something to do with molecular alignment.

Any comments on that? Was it snake oil?

The obvious answer is that< no, it was not snake oil. It was magnetic field therapy! Snake oil has little effect on molecular structure though it can alter the pressure curve due to it's lubricity. I look forward to an honest comparison between snake oil and moly as a barrel conditioner. Regards, Bill.

Matt,

Everyone knows that Gremlins exist! How else can you explain the loss of accuracy when a firearm resides in a safe between firings?

Pyrotek,

Look at Precision Shooting for an older article on what has now become know as the "Houston Warehouse". It is an extensive article on some of what you are asking about.

Bill

The sonic velocity in steel is far greater sonic velocity in air. If memory serves it is somewhere in the range of 3-4k Meters/Sec.

This implies (to me) that when the striker falls, the vibrations have traversed the barrel several times before ignition occurs.

IMO, This may explain why changing a striker spring can change the load tuning.

Memory didn't serve me. I was low in my guess.

http://www.radiatronics.com/guides/guide_vel_low.htm

[This message has been edited by Scott H (edited 12-29-2001).]

Zutz wrote mostly about shotguns and it was probably a trap gun he was talking about because everyone knows trapshooters are crazy and will do almost anything to break more targets and cost be damned.

Zero Drift __

The reason that cryogenic treatment works is that when the barrel is put through a "normal" treatment of quench and temper, there are regions within the steel that do not all transform uniformly from austenite to martensite to tempered martensite. This is a matter of the varying temperature gradients within the steel during thermal processing. Each crystalline product involves a change in dimension which induces varying stresses within the bulk of the steel. Cryo treatment transforms any residual austenite to martensite which, upon subsequent tempering, makes the crystalline structure all the same. It is not stress-free, but any residual stress is now uniform. It will now respond to external loads with equal uniformity.

One problem that has been experienced with cryo treatment of rifle barrels is that the hype of the facilities doing the work claim that fully finished barrels can be treated with excellent results. Not so. The process, in transforming local "hard" or "soft" spots will result in the aforementioned changes in dimensions which can throw a finished barrel out-of-straight, hence influencing accuracy. The best time to cryo treat a barrel is prior to finish machining and straightening.

My apologies for the long monologue.

Good shooting.

Robert

[This message has been edited by bobshawn (edited 12-29-2001).]

Thanks for the reply.

I once heard the U.S. military did an experiment : They removed the handguard of a couple M-16s and fixed the barrel in a block of cement (i.e. pour it on the gun and let the concrete set) so the barrel cannot vibrate. The gun is then fired into paper targets.

Anyone ever heard about the results?

Pyro,

There used to be a device called the AccuMagic Accurizer IIRC that you inletted into the fore end of the stock. You could turn a screw and adjust the fore and aft position of a bedding vee block that pressed against the barrel to find the best position for a particular load. The guy who invented it had quite a bit of data showing how well it could shrink groups.

jim dodd

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