I've been reading a ton of mixed answer to the question...

I will be shooting 3 gun and I am curious if I was to use a rifled slug which choke tube is the tighest that you can use in order to correctly lauch this thing?

Also, I cast/reload these type of slugs

I understand its not a rifled slug and it will not fly correctly but will this also hold true for this type of slug as for rifled slugs(I'm just curious... I will not use this in a smooth barrel)

Mike.

A full choke is safe for rifled slugs.  I wouldn't use extra full or a turkey choke but full is perfectly fine.  If you're using factory shells they usually say right on the box "safe for use with all chokes" or something like that.  I usually get the best accuracy with Modified though.