straight Particle shoot suddenly flies weird - bug?

Dear community,

I set up an emitter for an aim and shoot game. The emitter is child of a rigged character arm which is moving. Unluckily I cannot get my particle to fly a straight line , at some point it gets some weird influence and flies a turn... maybe a global/local space issue?

Any ideas how to fix it? 
Can I somehow use "pin to mesh" to keep the emitter out of it´s child hirarchy and still bind it to the rigged arm? (I found it hard to work with that component since there is no realtime visual feedback.

-----EDITED:

I found that the particle follows the emitter movement even after it got spawned... since my arm is moving, the flightpath follows the shakiy movement of the rigged (parent)arm.

Now that I know, does anyone know a solution for that issue?

 cheers people,
eL