Modern sniper rifles, from the 1960s onwards, have been increasingly purpose-built. The critical goal is reliable placement of the first shot within one MOA (minute of angle). Most include special features for this purpose, including tight building tolerances and precise components. Measures are also taken to ensure the rifle is affected as little as possible by heating, vibration and other effects which may reduce accuracy. Besides that, purpose-built sniper rifle systems often offer factory made accessories like telescopic sight mounting sets, MIL-STD-1913 rails (Picatinny rails), auxiliary iron sights for emergency use, cleaning kits, muzzle brakes/flash-hiders and sound suppressors (silencers), monopods (buttspikes), bipods, handstops, mirage bands, soft and heavy-duty transit cases and various maintenance tools. An example of a non-factory-made accessory could be shooting sticks that can be employed as rifle field rest.