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The free floating barrel
The key to accuracy in shooting is consistency. This simple truth would
seem not to bear mentioning, but keeping it in mind will vastly simplify
attempts at accurizing. When a firearm is discharged a number of factors
conspire to add variations and inconsistencies to the mix. Recoil, which
would seem to have the largest effect, in reality has the least. The motion
of the bolt has some effect. In a bolt action rifle, this can be minimized
by making the bolt as tight fitting and as smoothly operating as possible.
The ideal would be to have no clearance, no tolerance at all between the
bolt and the receiver. This is, clearly, not possible. In a specially tuned
match gun, the bolt may be made oversized and then hand fitted to the receiver,
and to the barrel, by a gunsmith. This type of operation will reduce the
clearances as much as possible without binding the bolt, so that when the
bolt is locked in preparation for firing, it will lock in the exact same
place every time.
In a semi automatic things get much more difficult because the bolt, and a number of other parts are usually in motion while the bullet is still moving down the bore. At first it would seem as if the goal in accurizing the gun would be to minimize this motion as much as possible, and there is a certain amount of merit in that approach. More important than minimizing this motion is making sure that the movement of the parts is the same every time. So it is consistency of motion rather than reduction of motion which will have the greatest effect on accuracy. Having belabored this point I will now get into how a free floating barrel works. The barrel has the greatest effect on the accuracy of a gun of any component.
When a bullet is forced at high speed up a gun barrel, the barrel flexes and whips about. Rifling the barrel to spin the bullet complicates the barrel whip. At one time it was thought that the best way to accurize a rifle was to put as stiff and heavy a barrel as possible on it, and to try to limit barrel whip by any means. The results were spotty. Glass bedding was popular for a while. This procedure used a fiberglass resin to bind the barrel to the forend stock, and often to special metal stiffeners which were embedded in the forend stock. The problem with this procedure was that it often did not work, and could even make the rifle less accurate. Mating the barrel to the stock meant mating the barrel to any imperfections or changes in density within the stock. It also meant that if the stock should begin to warp, or if it or the glass bedding material should swell, shrink or crack, that the accuracy of the rifle would be destroyed. It also meant that every time the shooter grasped the forend of the rifle, the barrel whip would be affected.
Present thinking is that the best way to an accurate gun is to take the stiffest heaviest barrel and isolate it as completely as possible. An absolutely free floating barrel touches nothing except the front of the receiver were the chamber meets the bolt. The barrel is allowed to whip and flex as much as it likes with no interference. In theory, with no outside influence, the barrel should flex the same way every time. In practice this works pretty well and is much more reliable than any attempt to limit barrel whip.