I have an "in" with a local art foundry.  They can cast brass and bronze objects of hundreds of pounds.  They charge by the pound.  I was thinking of making a wood pattern for a shipboard cannon, maybe 4', on my lathe.  I could add decorative works as appications on the wood pattern.  trunnions would be cast with the barrel.  Then make a green sand mould.  Get it cast.  Drill the bore on my lathe and sleeve with a seamless steel liner.  I have a lathe large enough to do the job.  Was thinking of a soda can, or juice can size bore.  Are golf balls worth messing with, or do they just shed the outer covering?   Any experiences with bronze as a gun barrel material?  Off my rocker or sound like a plan? 
Epoxy the liner or solder?  Make a flat end drill bit to make the flat end of the liner bear on metal?