I had to do the same thing years ago because mine was missing. It was a Century U-fixem that I got up and running. I'm not quite sure, but I want to say that it was not under tension when I installed mine. Even the online instructions say "Ejector and Automatic Safety. The frame may be swaged on both sides to retain the ejector pin (6), or the pin may just slide out" That to me would indicate that it probably isn't under spring tension. Good luck.