spread with 320 mm twist rate barrels in a 5-shot group. The precision requirements demanded of the SVD with 7N1 is similar to the American M24 Sniper Weapon System with M118SB cartridges (1.18 MOA extreme vertical spread) and the M110 Semi-Automatic Sniper System with M118LR ammunition (1.27 MOA extreme vertical spread). 7N1 differed from the standard LPS Gzh (57-N-323S) cartridge in its use of finely extruded propellant and a modified projectile containing a void inside of the jacket at the tip which improved terminal ballistics and a bimetal lead and mild steel core. With standard 57-N-323S cartridges, the precision of the SVD is reduced to 2.21 MOA extreme vertical spread. This ammunition was later replaced by 7N14 in 1999, which replaced the mild steel penetrator with a hardened steel penetrator in response to the development of infantry body armor. Sights The rifle features adjustable iron sights with a sliding tangent rear sight, graduated from in increments. The iron sights can be used with or without the standard issue optical sight in place. This is possible because the scope mount does not block the area between the front and rear sights. The SVD was originally issued with a detachable PSO-1 optical sight (now PSO-1M2) which mounts to a Warsaw Pact rail on the left side of the receiver. The PSO-1 elevation turret features bullet drop compensation (BDC) in or increments for engaging point and area targets at ranges from up to . At longer distances the shooter must use the chevrons that would shift the trajectory by per each chevron. The BDC feature must be tuned at the factory for the particular ballistic trajectory of a particular combination of rifle and cartridge at a predefined air density. With increasing range, inevitable BDC-induced errors will occur when the environmental and meteorological circumstances deviate from the predefined circumstances for which the BDC was calibrated. Marksmen can be trained to understand the main forces acting on the projectile and their effect on their particular gun and ammunition, and the effects of external factors at longer ranges to counter these errors. The PSO-1 sight enables area targets to be engaged at ranges upwards of ; effective ranges in combat situations have been stated at between , depending on the nature of the target (point or area target) quality of ammunition and skill of the shooter. Several military issue alternative telescopic sights with varying levels of