Ok, the MM 2k9 is cocker threaded right?

Cause I'm confused now. I can thread in my deadly winds CF barrel into my MM 2k9 body with no trouble. But the freak back and spyder to cocker adaptor I have lock up almost as soon as the threads make. And all three barrels make up fine in my other cocker threaded markers. I'm just confused about what would cause one barrel to work and the others not, are the tolerances really that close? I know to not force them together but am now worried about being able to use a freak back with it, I'd like to have the body/barrel all annoed with the same color theme.