Greetings,
there is a quie annoying bug in arma 3 right now that also were reported by M7SNK at forum http://forums.bistudio.com/showthread.php?187634-BUG-artillery-scope-does-not-show-charge-type&p=2857487#post2857487
If you are using artillery through scope without artillery computer you can not see the type of charge you are using, therefor rendering using artillery without artillery comp impossible.
FIREMODE DOES NOT SHOW UP ON ARTILLERY SCOPE and the only way to see it is by checking on artillery computer {F25400}