+ on the locking bolts!
I'm betting that the locking bolts on the 30-30 barrel are not engaging far enough. It's actually a common problem with Contender barrels. Give the locking bolts a good cleaning and make sure that they have plenty of spring tention in them. Those things must fully engage the interlock in the frame for the gun to go bang.
If you have verified that the bolts are cleaned, lightly lubed, and have plenty of tension, and the gun still won't fire, then you may need to polish them. Just drive out the roll pin that holds them in being careful not to loose the spring. Take a hard sharpening stone and some oil and polish the sides of the bolts that meet the inside of the frame. You might also give the tops of them a little attention also. Be careful! You're not trying to grind them down, just polish them until they snap into the frame correctly. I've heard of some folks using a Sharpie to color the bolts, then polish until you remove the ink (do this a couple of times). Polish a little, install, test, repeat until they fit correctly.
I'm actually surprised that the hammer will even cock, but each Contender frame is slightly different, not matter how much alike they all are.