The lockup or stiff point, is about how from closed?
Just an idea that maybe its an adjustable throw which is unlikley if its stock and not modified.
If so, maybe it's out of adjustment?, but that is a stretch.
I am thinking that you have an obstruction of some kind on the pump wall. Crusted dirt and oil etc.
Another ldea am thinking is that someone oiled it and you can't compress oil. For either of those problems you can flush it with cleaner degreaser.
I use a foaming spray and a tiny glue tip to get it into the air hole. Then just shoot and repeat it till its clean.
If that doesn't do it, the next thing would be to drive out the front block pins2, Remove the block, slide the pump out, then align the last pin in the pump lever with pump arm pivot hole, remove that pin then the pump will come out. Then you can have a look in the chamber and give it a good cleaning, and maybe replace the pump plumger while you have in apart.