=10. The Sighting of Rifles.=--(i) In the sighting of rifles a _mean graduation for each range has been adopted_, and a high general standard of accuracy for all practical purposes is thus obtained. Each rifle is carefully tested before issue, but it must be understood that _no two rifles behave in an exactly similar manner_, and that even if compensation could be made for every error in the sighting of the rifle before issue, the wear of parts and the loosening or tightening of screws, etc., would bring about faults from time to time which would affect the shooting of each rifle differently. =11. Need of Knowledge of Each Weapon.=--_It is therefore necessary that every man should study the shooting of his own rifle_, and make himself acquainted with any incorrectness of the graduations marked on the backsight, in order that he may be in a position to give his rifle the correct elevation for the estimated or ascertained range of the target. _At longer ranges the backsight elevation may be regarded as the best possible guide to errors under all conditions, or any error may be ascertained by using a long-range sighting target._[7] =12. Jump.=--Owing to the shock of discharge, a vibratory or wavy motion is set up in the barrel, which slightly affects the line of departure of the bullet as it leaves the muzzle, and which is known as “jump.” The causes and extent of jump are dealt with in the textbook of _Small Arms_. The effect of jump is allowed for in the sighting of the rifle, _and will not be taken into account by the soldier in aiming_. =13. Drift.=--Drift is the term used to express the _lateral deviation_ of the bullet after it has left the barrel. This is due to the direction of the rifling, which causes the bullet to rotate from right over to the left in its flight, so that the point works over slightly to the left, owing to gyroscopic action. The consequent increased air-pressure on the right side of the bullet forces it to the left as it flies. _The deflection due to drift at distances within 1,000 yards is negligible, and need not be taken into account by the soldier in individual firing._ Beyond 1,000 yards up to the limit of effective rifle fire at about 1,400 yards, drift will carry the bullet about 7 feet to the left. This deflection, if necessary, will be taken into account by fire-unit commanders in directing concentrated fire at narrow-fronted targets at longer ranges. =14. Effect of Fixing the Bayonet.=--(i) When the bayonet is fixed to the muzzle of the rifle, its weight checks the jump, and in consequence slightly affects the position of the muzzle at the moment of the departure of the shot, and the primary direction given to the bullet. (ii) =Short Magazine Lee-Enfield Rifle.=--With Mark VI ammunition, the accuracy of the short magazine Lee-Enfield rifle is not appreciably affected by fixing the bayonet. With Mark VII ammunition, the soldier will aim down slightly in firing with fixed bayonet at ranges up to 600 yards.