TDS is the take down special. 16 1/4 inch barrel, both halfs the same size.
It is a handy little rifle. Truck gun ect. It you can't get it to group with iron sights add a scope to the top. Some people have trouble getting a good sight pictre for tree rats with the short barrel and Iron sights.
I have one I made so a sort of TDS. I bought the TDS barrel from numrich a few years ago and placed it on a 39a action. I prefer the longer barreled mountie or the 24 inch regular 39.