Winchester 62A want slide 100% open

My 62A 252XXX will not slide open more than 1/3rd the correct distance. The sile seems to hit a brick wall and will not advance any further. Please pass along any ideas for why this is happening. I am needing to reinstall the firing pin (removed by previous owner) but not being able to cycle the slide has me at a stopping place right.
Any help is welcome. If I haven't provided enough information let me know what additional info is needed in order to provide the correct fix.
Thanks