Do you have a hammer extension on your Contender? Yeah, I know that may sound a bit odd at first, but my shootin buddy was shootin 22lr for sillohuette for 6 months, and then decided to buy a 223 barrel.
He had the same problems of mis-fires and called T\C. The first question they ask him was about the hammer extension.
Well, since it was worth a try, he took off the extension and never had a mis-fire after that. It seems the hammer extension has enough weight, with an older weak spring, that it will not allow the hammer to develop enough momentum to strike the primer with enough force to ignite it.
So, if you have a hammer extension...take it off. What do you have to lose.
BTW, I had an extension on mine. After that, I have been shooting mine without an extension. Once you are use to it, It's no big deal.
Dave