of conventional bolt-action rifles typically lie between 2.6 to 9.0 milliseconds. Further reductions in lock time, to near zero levels, can be achieved with electrical primers. Bullet dwell time The bullet dwell time is the time between ignition of the cartridge and when the bullet leaves the barrel. Like lock time, dwell time is a window for error, and can be minimized with a faster bullet or a shorter barrel. In some cases, a shorter barrel is desired to reduce dwell time, but without losing the sight radius of a longer barrel. In this case, a sight extension tube, or bloop tube, can be used. This is a tube that fits on the muzzle end of the barrel, providing support for the front sight, but that is bored to much larger than bore diameter. This provides the sight plane of a long barrel with less weight and dwell time. To put lock time and bullet dwell time in perspective; the lock time of most conventional bolt action rifles varies between 2.6 and 9.0 milliseconds, while after cartridge ignition most rifle bullets travel through a high powered rifle barrel bore in 1.0 to 1.5 milliseconds. Mechanical bolt-action rifle trigger systems with a sub 2.0 millisecond lock time are applied in most purpose designed high end competition rifles. Clearances and Tolerances The terms "clearance" and "tolerance" are very often confused and misused. Clearance is the distance between the surfaces of mating parts. Tolerance is the allowable variation of a dimension from its nominal (desired) value. For example, a bolt with an outside diameter (OD) of 0.697 inches which is operating in a receiver with a bolt raceway inside diameter (ID) of 0.702 has a clearance of 0.005 inches. If the bolt OD has a nominal OD of 0.698 and a tolerance of +/- 0.001, then the bolt OD can randomly vary from 0.697 to 0.699 along its length, which will allow the bolt clearance in the 0.702 diameter raceway to vary from 0.005 to 0.003. Further, if the raceway also has a tolerance of +/- 0.001 from the nominal of 0.702, then its ID can vary from 0.701 to 0.703 along its length. That combination of tolerances can allow the bolt clearance to vary from 0.002 to 0.006. The point at which the 0.002 clearance occurred would likely cause binding and malfunction in most operational environments. To ensure consistent, repeatable lockup, clearances