How to match arm position & rotation when Switching from FK to IK for the arm?

Hi Judisak,  I don't have any tricks to matching when switching.  I didn't build snapping into the rigs.  But here's some advice for doing it by eye.

-Make sure you key both the IK and FK on the switch.

-switch over 1 frame (key both IK and FK on both frames as mentioned above)

-try to avoid switching at all and stick with either IK or FK on that body part for the entire shot (probably not possible in this circumstance)

-try to switch during a move so it is easy to flip the frames and match the motion - OR 

-try to switch when it is perfect still, so when you flip the frames you can see when it isn't matching and tweak it easily.

(The last 2 tips depend on the situation.  1 way is usually easier in different shots)

Hope that helps.