Howdy Cat, 
             I have been introduced to a whole new aspect of metalwork, this boring out of cannon barrels.  Is that one machine I see in your photo?
If so I gotta get me one of those!  A friend, upon seeing the cannon site of ya'll's...  said: 
 "Is that work done with a lathe"?
I was impressed, {I took wood shop}
I assumed that a lathe was for doing table legs.
But it is reasonable that a 'lathe' can bore too, 
Your machine had the 'thing to be bored' turning and the drill bit stationary, with some oily looking crap dripping on it as it  drilled or bored.
     {What is the difference between drilling and boring?
So, is the cheapest  'Grizzly'  lathe capable of holding a chuck big enough to support a 2" drill?  I have a Grizzly 2"x72" knife grinder, and I love their bandsaw too.  How big is the chuck on a 2" drill bit?
            The 'Griz' has a   {3" chuck  with a 3 side jaw 

 }                     and it is about   $525,00   with shipping. 
Would a drill press do?
     What did folks do 2-300 years ago?
       A thousand years ago...  if they wanted to bore out a cannon?
          Slave labor it on out?
             But with what?      
   It would seem that if I can't afford a boring set-up before Sept.    I won't be able to amaze the world with my new mortar,  dern!
A piece of pipe 1/4 - 1/2" thick steel walls,  and a size I could duplicate by ...dog food cans?
Tomato sauce cans?
Grapefruit juice ?
             I'll have to search for cans and pipe till I just find a match-up.
                          Seems easier than grinding those suckers down.
                                      Lots of trash in the world 
                                                     An interesting problem?
                                                                                                                                     J. Knife