I have a Contender with a 12" Bullberry barrel chambered in .221 Fireball that is topped with a Burris 7X LER scope. Use to team up with my son on prairie dogs, he shot a .223 prone and I shot the Contender off a bench made from an old camera tripod. When laying prone the dog was his if he could see it, if he could not see it and I could because of the extra 2 feet of elevation, then that dog was mine.

I also have another with a older barrel that has been re-chambered in .410. Use that basically for close range vermin control in my yard and not much more.
Pretty much what minnesothaunter says, make sure it locks up tight and maybe any indications of home gunsmithing.
How old of Contender? I believe there are at least 3 styles of Contenders out there as far as the rimfire/centerfire selector goes. The newer models I believe have a selector on the top of the hammer, the middle generation has a sliding bar in the hammer to select and I think the oldest models a screwdriver has to be used to select between rimfire and centerfire. May be wrong on this, hopefully someone that has more knowledge will step up with correct info if I am.