It sounds like you've owned a few contenders.
This is my second one, I had a Gen1 before this.
In a conversation that I had with Gary Reeder, he told me that there are some G2s that will only fit nbarrels that he has made for them.
In another conversation with Mike Belm, he told me that there have been design changes for different series of Contender frames within each generation.
This discussion is a bit premature because my frame is still in the FFL shop where it will have to stay for another 9 days from today before I'll be able to pick it up.
I did have a chance to try out my barrel, a .41 mag from an older contender from back in the days when the factory still produced .41 mag barrels. The dealer let me try my barrel out at the counter to see how the fit is. It would snap shut nicely but I couldn't cock the hammer. Something that's interesting is that on a different G2 that he has my barrel fit perfectly and there was no hammer cocking issue.
That's all I can say for now. If I could I'd send it back or trade. I got it online.There's good news though, TC (S&W) offers a rebate of $75 for purchaces made during 2017
Maybe I'll collect the rebate first then send it back, that will compensate me for the transfer fees lost.
It's difficult to recommend buying a Contender to a friend, knowing the issues with barrel fit. Every bit of literature out there from the company says that any barrel made will fit my frame, and that is simply untrue.