1. Field of the Invention
The invention relates to rifle actions in general and bolt actions in particular.
2. Prior Art
In a bolt action rifle, the barrel is typically threaded into the receiver. The barrel includes the chamber, which is that portion of the barrel that holds the round immediately prior to firing. The rough dimensions of the chamber are formed prior to the barrel being threaded into the receiver. However, the final dimensions of the chamber are formed by hand in order to ensure that the headspace is proper.
Headspace is the distance from the face of the bolt to whatever surface in the chamber stops the round from advancing into the barrel. In a rimless cartridge, such as the .308, the headspace is the distance from the bolt face to the shoulder in the chamber. Stated more broadly, in a rimless cartridge, the headspace is a function of the distance from the face of the bolt to the chamber and of the chamber dimensions. Headspace in a rimless cartridge is illustrated in FIG. 1 as dimension X.
The acceptable tolerance for headspace in rifles is relatively narrow. In a .308, the acceptable headspace range is 1.6300 to 1.6340 inches. Thus, only 4 thousandths of an inch separate too little headspace from too much.
Very bad things can happen if the headspace is not within specification for the rifle. When the round is fired, the chamber is supposed to hold the casing in place so that the expanding (i.e., exploding) gases can be used to drive the bullet down the barrel. However, if there is too much headspace, those same gases can drive the casing back toward the bolt. This can result in failure of the casing, damage to the bolt, and in some cases, even catastrophic failure of the rifle. Excessive headspace can also result in the round advancing into the chamber so that the firing pin in the bolt cannot adequately impact the primer, with the result that the round fails to go off. Similarly, excessive headspace can allow the spent shell casing to slide forward into the chamber so that it cannot be extracted, which can preclude the rifle from being reloaded—an annoyance in the best of circumstances and a potentially deadly occurrence to the shooter in certain conditions, such as self-defense applications and dangerous game hunting.
Insufficient headspace can be a serious problem as well. If the bolt is closed on a round in a rifle with insufficient headspace, the bolt may be exerting tension on the casing in the chamber. This can lead to casing failure, resulting in the emission of the hot expanding powder gases into the chamber. This can result in catastrophic failure of the rifle and/or emission of hot gases directly into the face of the shooter. It can also result in a portion of a failed casing not extracting from the chamber.
Because of the close tolerances required of headspace and the significant risks associated with the operation of a rifle whose headspace is out of specification, the chambering of a rifle is typically finished by hand. First, the rifle will be rough chambered. Then, the gunsmith installing the barrel must manually ream the chamber, very slowly. He turns the reamer, measures the headspace, and then turns the reamer some more, until the headspace measurement is correct. This is a very time consuming process, and it is a substantial factor in the cost of rifle manufacturing as well as after market barrel replacement.
In view of the foregoing, a bolt action rifle meeting the following objectives is desired.