Good for slugs?
 

Hello, I have a single shot 20ga smooth bore with a fixed full choke, I was wondering if it was safe or even usable to shoot any kind of slugs thru?

You can, but don't expect any kind of accuracy.

I have shot slugs thru a 12 ga with a fixed modified pretty succesfuly and also tried a 20 ga with a fixed full not so succesfuly.

I think you will find most gun manufacturers will state that they do NOT recommend anything tighter then a mod choke some will say NOT tighter then an Improved Cylinder

Ok thanks, i can just get a slug barrel for under $80 any way probably work better any how.

if you get a rifled slug barrel make sure you get slugs for a rifled barrel.Like hornady SST slugs.I use them and the awsome.just have to shoot them to see if your shotgun likes them.