possiblities... and drawbacks
#1 the rifling is still hidden underneath a really bad case of leading....
#2 it came unrifled from the factory
#3 it was altered (bored out) to a smoothbore after it left the factory'
#4 The gun has been shot so much the rifling is worn away...
#1 is likely, #2 is possible, but not likely, so are #3 & #4 (and if the gun was shot enough to wear away ALL the rifling, odds are the overall condtion will show a lot of wear. Since you didn't mention that, I doubt that's the case.
If the gun left the factory as a smoothbore, it would be a rare, and collectable gun BUT, it is also an NFA item (essentially a sawed off shotgun). Posession of such an item without the federal paperwork and tax stamp is a crime. No matter how you came to have it.
I recommend you contact a good firearms lawyer, and seek advice on the proper way to proceed. At this point, you may be legally able to send it back to Colt to get it "fixed", OR you may not have any legal option other than surrender the gun to the ATF. Or you may have an option in between.
I can't tell you. Get a lawyer, and do what they tell you. Let them deal with the ATF on your behalf, when necessary. Anything else and you risk prosecution, potentially ruinous costs for your legal defense, and ultimately, you still might lose, and be facing years in prison, huge fines, and loss of your right to own firearms, ever again.
This is not a joke, and not a minor matter. Get a firearms lawyer (the NRA may be able to recommened someone in your area), and play the hand you have been dealt.
Best case, you get to send the gun in to be fixed, no charges
Next best, you register the gun with the ATF and get to keep it, no charges
next best, you have to surrender the gun, but face no charges
worst, you face charges (and lose the gun anyway).
DO NOT DELAY, don't pretend the problem wil go away, it won't. you & your dad are potentially on the hook for some serious trouble...
Of course,if the barrel is just really badly leaded, and continued cleaning shows you that there is actually rifling, then its no big deal.
But if is a true smoothbore (no matter how it got that way), get that lawyer!
I would also recommend not discussing it further on the internet, until after you have spoken to your lawyer. Once you have resolved the situation, please come back and let us know how it went.