Streamline barrel alternatives

I was actually wondering if three were a direct replacement like the 600mm ST barrel from wildcat MK1 or Impact, if it were a drop in replacement. Interesting if I could make a STX with slug liner swap but sounds kind of expensive I guess. I'd probably have to get a Huma reg too. Wonder if anyone has removed the reg to make a high powered hunting rig but I tend to do this will all my .22's... I like how compact, light and quick this gun is to handle and don't know what direction I want to go with it, first is knowing what the options and cost are though.