Orange armor piercing (S.m.K.) tracer (L'spur) improved (v). Ignites at 100 meters and goes out at 600 meters. S.m.K meant armor piercing.   L'spur is an abbreviation for Leuchtspur which meant bright tracer to be used primarily in the daytime.   The small black tip on the bullet is an indicator for tracer. The "v" (indicated by the green stripe) was used for ammo that was higher velocity in an attempt to get better performance out of aircraft machine guns that were becoming obsolete.  The hotter loading also reduced the life of the machine gun barrels.  These rounds were not for use in a rifle.   The delayed tracer was used to avoid revealing the location of the gunner and also used in aircraft machine gun belts as a warning that ammo in the belt was running low. NOTE:  The exact information about a given round can only be found on the box label.  Once the round is separated from the original box, only basic information is available from the markings on the round.