I have a TC Hawken which I lent to an ex-friend. He didn't return it for two years, and he didn't clean it. The rifling was trashed.
I took the barrel to a machinist who I know. I brought a drill bit, I think it was a .531.
He welded the drill bit onto a long steel rod. He clamped the barrel into this giant green steel machine. He fitted the now 32 inch drill bit into that machine, and he drilled out the rifling. A little hose squirted machine oil into the barrel the whole time. Took about 20 minutes of drilling.
He did this for me for free, don't know what a customer would get charged.
This left some scoring in the barrel, which I never bothered to smooth out.
I was shooting #12 rat shot to try to knock down carpenter bees that want to eat my log cabin. To my dismay, this was not a very good shotgun. Past 20 feet the shot was so spread out I couldn't even hit a bee. Very small bore for a shotgun.
I think you would be hard pressed to make a good squirrel or rabbit gun out of one of these, although I never tried any larger shot.