what is AB, SC,..,..

[beginner]

what sort of a bombs are AB or SC?

why most of the times my bombs doesnt explode? i set..nothing, or INSTANT..
specialy on f4u corsair, 500kg bombs, the never exploded. i did already some tracks. 1. few times i slice them on sea surface..they beautifully jumped to the ship...a never, never exploded..( 2. also i hitted board of the ship, the bomb goes inside the ship....and no explosion..

and also i dont know.., when i set airbrakes on STUKA and start to go straihgt down, after while bomb flyies away itself...so i cannt aim..., i never drop the bombe..she drop itself allways...

is there somwhere a manual? for new versions of Il2? also for mig 17.., missiles..and so..

thx!!