The barrels are sleeved. When I say sleeved, I mean monoblocked as some call it. Jack might have thought about tube inserts or something when you mentioned sleeved.
Like I said, what was done was the ribs were removed, the barrels were cut off in front of the chambers and new tubes were fitted (or sleeved) to the original monoblock. Then the ribs reinstalled.
It is a fine way to rebuild a set of barrels if the person doing it knew what they were doing.
I have a double rifled slug gun being build right now with this same method.

Thank you for the detailed explanation. I apologize for the confusion.

I took possession of my AyA 4/53 on Saturday. Will shoot a round of sporting clays with my brother on the fourth. Today is my birthday. I am afraid while I am on the course I will be thinking of the Parker.

Thanks again.

Happy Birthday!

Thanks.

Not much better to do on your birthday than go out and shoot a round or two.