You're better off creating the spell you wish the weapon to cast and using opcode 146 Cast Spell instead of involving EFFs. You can look at Harbinger (sw2h07) or the Club of Detonation (blun27) for examples.
Just did it. Worked like a dream.

Thanks man!
Got a couple of more questions though...
1.) I recently re-edited the palette of a SPBASEWT (think that's the name) with
DLTCEP and saved it under a name of my choice.
I tried using that effect, but the animation ends up behind the character. Not in front. Now I can understand that the setting
should be to 0 (Play on place cast), but it doesn't work. If I change the Play 3D setting to 1 (play over target), there is no difference.
Do you know what that might be?
2.) I am building a weapon which uses 3 special moves, where 2 of them are limited but rechargable. The problem is, when I get that weapon through the console,
there is only 1 charge in one of the two limited special moves. If I use the move that has 1 charge - or if I use the infinite special move - the third limited
special move, will suddenly have tens of thousands charges. I haven't been able to fix this... xD