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Freefloating a rifle barrel, please input information for Johny Five.

Discussion in 'Large-Bore/Small-Bore Rifle/Shotgun' started by Mosin_Nagant_Fan, Apr 27, 2007.

  1. Mosin_Nagant_Fan

    Mosin_Nagant_Fan Active Member

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    I have an idea of what it is, but how to do it is one thing I wish to know.

    I have a sportsatized Mosin-Nagant stock that I'm willing to try this on, if possible, but I need to know what significant purpose it would provide my rifle.
    Last edited: Apr 27, 2007
  2. 300 H&H

    300 H&H Active Member

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    Mosin; free floatin barrels don' touch the stock any where except maybe the first inch or so. in front of the reciever. The idea is simple. A barrel vibrates in two ways, this first is in the form of a sine wave, like a rope if you were to grab the end and whip it quickly up and down, the second vibational pattern is best viewed from the rear of the barrel. imagine the butt of the barrel fixed and the front of the barrell drawing a circle(small) in the direction opposite the rotation of the bullet that is being spun buy the rifling in the barrel. If anything is touching the barrel, that interferes with it's ability to vibrate freely. Best accuracy is obtained when the bullet leaves the barrel at the same point in each vibration. Heavy barrels vibrate less so tend to be more accurate(also easier to hold steady)as with smaller vibrations they have (stiffer) change the striking point less. But a good spoter barrel can shoot as well if free floated, good ammo, and the barel does the same vibration each time with the bullet leaving in the same point in the vibration. Just like a tuning fork a free floating barrel will "ring" when the butt of the gun is struck and the length of it will determine the pitch of the ring. But the action beding, or the fit of the metal to the wood must be very good as it is carring the load of the floating barrel through it. And some times with light weight barrel, a rifle will shot best if there is a slight preasure applied at the tip of the forend of the stock, to dampen some of the whip of the vibrations. You must experiment to find out what is right for your rifle. Upward tension can be applied by a shim between the stock and the barrel near the tip of the forearm. Wood has to be removed in the barrel channel to "free" the barrel with a round rasp or file. 1/16" clearance is a good place to start. Good luck on your project Kirk
  3. LDBennett

    LDBennett Well-Known Member

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    To understand stock bedding and its implementation we must understand rifle barrels first. All things have a natural frequency at which they will ring, just like a tuning fork, when excited by the correct force. Barrels are no different. Fire the gun and the barrel has a desire to ring and move in an oscillatory fashion. Such ringing can be sustained but also can be quelled by either internal dampening or an external force. A tuning fork can be stopped by touching it. What happens is that the external mass added to the system changes the natural frequency of the combined tuning fork and “finger” and the oscillatory motion is quick dampened. Barrels are no different than tuning forks. When the gun goes off it starts the barrel oscillating. The end of the barrel whips up and down and left and right, perhaps in a circular fashion. How the barrel moves is a function of the input force (big charge vs little charge), barrel length, concentration of the mass on the barrel, and perhaps a few more things. When the stock touches the barrel it changes the natural frequency of oscillation and can act to dampen it for the force that was put into it (explosion of the cartridge powder). That is a good thing until the rifle gets bumped or the humidity changes how and where the stock pushes on the barrel or you move the gun on the bench bags. To get consistent results we must remove the variables. We want the barrel to move exactly the same with every shot.

    Once we isolate the barrel from any outside condition (like touching the stock) we can tailor the barrel mass (Browning BOSS system or LimbSaver rubber donuts on the barrel) or choose a heavier more massive barrel or tailor the input (change load of powder in the cartridge) to time the bullet exit to be at the end of the barrel whipping motion where the barrel is virtually stationary as it changes direction. Barrel bedding or floating eliminates variables and tries to make the barrel motion consistent with every shot.

    While free floating the barrel is ideal, adding a pressure point can change the system mass enough to move the tuned system frequency out of the range of the input force (explosion of cartridge powder), somewhat like touching the tuning fork. But the explosion of the cartridge powder contains so many frequencies that often the pressure point does not work as anticipated. With so many variables in the entire gun system the actual gun barrel motion can get complex. Free floating the barrel without a pressure point simplifies the system with respect to changes that the stock might cause as the weather changes or you move the gun on the bench bags. Once the barrel is free to repeat its oscillatory motion every shot, the loads can be changed to try to find the level of force input that lets the bullet exit when the barrel is a direction change null. If load level changes are not possible (limited selection of factory rimfire cartridges, for example) then barrel mass changes (BOSS System adjustments or LimbSaver donut use and adjustment or adding or subtracting barrel weights or changing the mass of the barrel through length changes or barrel contour selection) are necessary. Changes to the length of the barrel also affect the system.

    To get it all perfect requires lots of testing or you may luck into a gun that happens to have it all right by chance for the particular ammo you are shooting. The easiest way to approach this situation, at least in my mind, is to float the barrel and use other varibles (barrel mass, charge level, etc) to get the bullet to exit when the barrel is at a null in motion.

    Practically you may find the pressure point works but the force it exerts on the barrel can be a function the weather or where you set the gun on the bench bags. The gun may shoot great in July and not as good in December or great this shooting session and not so good the next when you set the gun on the bags differently. Total free floating make the most sense to me.

    LDBennett
  4. TRAP55

    TRAP55 Active Member

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  5. Mosin_Nagant_Fan

    Mosin_Nagant_Fan Active Member

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    Eh, seems more work then it's worth.
  6. TRAP55

    TRAP55 Active Member

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    Looks harder than it really is, but the results are impressive.
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