I would take it apart carefully and likely you will find what the problem is. The spring changers guild always recommends replacing springs, but unless one is rusty or mangled I have yet to replace one. If you get a defective coil spring, it will not look uniform. It does happen. Maybe there have also been some that just collapsed as well, but I have yet to see one. Modern coil springs do not wear out from sitting, compressed or not, but only by repeated cycling over many, many thousands of cycles. That is why coil springs have an advantage over leaf springs. I have seen more "sure cycle" kits mess up a gun than fix one. I would remove the recoil spring first so you aren't dealing with parts under spring tension. I used to work on a lot of guns. I never called myself a gunsmith because I have zero artistic ability, and wood hates me, but I was more than a fair hand as a gun mechanic. The owner's manual is usually your friend. All the people who talk about tweaking springs are not. Long recoil actions do need the components set up correctly for the loads you are shooting in some designs. As I recall the Model 50 was a short recoil/floating chamber design. A real simple action really, but the chamber was subject to fouling issues with the old shells as I recall. There was a good description on Wikipedia as I recall also. Do not force anything. Guns were not mean't to be disassembled with hammers until you get down to drift pins. Whatever is wrong, forcing things will only make it worse.
I believe the 50 and 59 were the same except for the fiberglass barrel on the 59. This may help.
50. WIN Accessories | Numrich Gun Parts

 

Thanks for the info!