First let me preface this by saying I looked at Bellm's webpage for parts reference, so I could be way off on my terminology.

I bought a used 45-70 barrel off of GB. I have had it for two weeks but just tonight put it on my frame. It mounted and locked-up fine, or so I think. But I can't cock the hammer. If I push the barrel into the frame I can cock it. When I mounted the barrel I noticed that the ejector was slightly rusty. Is it possible that the locking bolt spring may also be rusty/dirty and thus not allowing the locking bolt to engage and not allow the hammer to be cocked? If so, can the locking bolt spring be saved, ie. soak it in Hoppes or oil. Or does it need replaced. Or am I complete off here. Three other barrels lock up and allow the hammer to be cocked, so I'm pretty sure it is the 45-70 barrel and not the frame/action.

Thanks all.

Did you happen to change grips at the same time? Over tightening the grip screw will interfere with lock up. Otherwise, clean the heck out of every thing, pay close attention to the locking block too.

The handle was the first thing I checked, not that. If I'm pulling the locking bolt to clean it, probably just replace it.

To check the locking bolts, clean off the top surface and color it with a marker. When you close the action and then open it again you'll be able to see how much engagement there is. Based on your description, I'd guess not enough. Can either carefully stone down the top surface so it locks up better or replace them and see if that works.

With new barrels I always pull out the bolts and extractor to clean all that stuff up regardless.